These flares can be used for emergency pressure control on liquid ammonia tanks and for tank vapor control during cleaning and degassing.

Call Townsend Hilliard – 713-201-7517  or Hank Hilliard 713-828-7247 for immediate assistance.

Short video of the ammonia flare in operation:  Ammonia-gas-flare-night

Day time ammonia combustion

In most cases the condensate can be returned for recycling – either to the manufacturing plant or back to an adjoining tank of the same contents. Or it could be sold as cargo.

PURGIT mobile tank degassing is the best vapor control service available.

1. We can degas a tank without opening the tank up.

2. We make no pollution by burning the cargo and exhausting to the air.

3. Our work is absolutely verifiable.

4. We return the cargo as liquid for recycling.

We have mobile equipment using the most sophisticated technique available for tank degassing. It is clean, safe and efficient.

Call Townsend Hilliard for more information 713-201-7517

Pictons of Houston

Recipe Pages

Divider Pages

Cookbook cover

Rockport TX

Picton Tow Boat Company

The founder of the Picton Tow Boat Company was DM Picton. He died in 1937. His obituary says in part:
“The late Mr. Picton was a pioneer on the Texas coast in the construction of rock breakwaters and jetties and other type of large and difficult marine construction. In the last month of his illness it gave him considerable satisfaction that the company, which bore his name and which he headed as president, had completed the very difficult job of capping with concrete the long east jetty at Sabine pass.
This piece of work was reputed to be the most difficult piece of concrete pouring ever accomplished, and apparently insurmountable obstacles were overcome in the capping of the 6,900 foot jetty.
He lived in Rockport for 50 years. He was the contractor who built the Corpus Christi breakwater approximately 17 years ago, and he also built the jetties at Aransas Pass, Freeport, Galveston, Sabine Pass and the southwest pass in the Mississippi River.”

The Aransas Pass jetty would allow commercial development to expand toward Rockport TX or Corpus Christi TX. Both cities wanted development to go their way. Here are some old advertisements advocating bringing business in the direction of Rockport. As it turned out, the Corpus Christi development was more successful as growth went that way. Rockport today is a small town and artist colony. It is a great place to visit and live. There are many restaurants and it is a hub for sport fishing. Catches include red drum, speckled trout, flounder, etc.

Deep Water Harbor built in Port Aransas 6.1 mb .pdf file This is an advertisement for Rockport TX. It was hoped that the jetties built at Port Aransas would make Rockport more popular. This is a very interesting advertisement.

Rockport advertisement 5.7 mb .pdf file  Another advertisement for the city of Rockport TX and the Deep Water Harbor

DM Picton and his 5 sons ran the Picton Tow Boat Company and the company continued after his death. Here are some 1950 rate quotes for the Picton towing out of Port Arthur TX
Picton rate schedule 1950 this is a .pdf file If you want to see the complete map , you will have to print and then cut and paste. It shows steaming time in the Sabine district for the Picton Tow Boat Company.

Ports that Picton towing served in 1950 .pdf file This shows the ports served by Picton Towing out of Port Arthur TX

To the best of my knowledge, the  Picton Towing vessels were sold to Moran Towing about 1977.

Propeller Terms and Definitions

1. Diameter –The diameter of the imaginary circle scribed by the blade tips as the propeller rotates.

2. Radius –The distance from the axis of rotation to the blade tip. The radius multiplied by two is equal to the diameter.

3. Blade Face –Pressure Side, Pitch Side. Aft side of the blade surface facing the stern.

4. Blade Back –Suction Side. Forward side of the blade surface facing the bow.

5. Leading Edge –The edge of the propeller blade adjacent to the forward end of the hub. When viewing the propeller from astern, this edge is furthest away. The leading edge leads into the flow when providing forward thrust

6. Trailing Edge –The edge of the propeller adjacent to the aft end of the hub. When viewing the propeller from astern, this edge is closest The trailing edge retreats from the flow when providing forward thrust.

7. Blade Number –Equal to the number of blades on the propeller.

8. Blade Tip –Maximum reach of the blade from the center of the hub. Separates the leading and trailing edges.

9. Hub –Solid cylinder located at the center of the propeller. Bored to accommodate the engine shaft. Hub shapes include cylindrical, conical, radius & barreled.

10. Blade Root –Fillet area. The region of transition from the blade surfaces and edges to the hub periphery. The area where the blade attaches to the hub.

11. Rotation (Right hand shown here) –When viewed from the stern (facing forward): Right-hand propellers rotate clock wise to provide forward thrust. Left-hand propellers rotate counter-clockwise to provide forward thrust.

12. Pitch –The linear distance that a propeller would move in one revolution with no slippage.

13. Cylindrical Section –A cross section of a blade cut by a circular cylinder whose centerline is the propeller

14. Pitch –Reference line Reference line used to establish the geometric pitch ang1e for the section. This line may pass through the leading and trailing edges of the section and may be equivalent to the chord line.

15. * Geometric Pitch Angle –The angle between the pitch reference line and a line perpendicular to the propeller axis of rotation.

16. * Controllable Pitch Propeller –The propeller blades mount separately on the hub, each on an axis of rotation, allowing a change of itch in the blades and thus the propeller.

17* Fixed Pitch Propeller –The propeller blades are permanently mounted and do not allow a change in the propeller pitch.

18.* Constant Pitch Propeller –The propeller blades have the same value of pitch from root to tip and from leading edge to trailing edge.

19;* Variable Pitch Propeller –The propeller blades have sections designed with varying values of local face pitch on the pitch side or blade face.

20.* Rake –The fore or aft slant of a blade with respect to a line perpendicular to the propeller axis of rotation.

20a. Aft Rake –Positive rake. Blade slant towards aft end of hub.

20b. Forward Rake – Negative rake. Blade slant towards forward end of hub.

21. Track –The absolute difference of the actual individual blade rake distributions to the other blade rake distributions. Always a positive value and represents the spread between individual blade rake distributions.

22.* Skew –The transverse sweeping of a blade such that viewing the blades from fore or aft shows an asymmetrical shape.

22a. Aft Skew –Positive Skew. Blade sweep in direction opposite of rotation.

22b Froward Skew –Negative Skew. Blade sweep in same direction as rotation.

23 . Cup –Small radius of curvature located on the trailing edge of blade.

24. DAR. –Developed Area Ratio is blade area expressed as the percentage of a circle shaded by the propeller.

* denotes terms that do not have a graphic representation to aid in definition.

Any cracking in the hub of a marine propeller must be regarded as serious, and any steps which can be taken to prevent such cracking are desirable. The purpose of this paper is to enumerate some of the more obvious causes of hub cracking and to suggest certain precautionary practices which can be adopted by all those who are vitally interested in the alleviation of the problem.

It is suggested that there are at least four principal causes of hub cracking. These are listed in what is perhaps the order of their importance.

1. Excessive heating at installation or removal.
2. Improper fit of key in keyways.
3. Improper fit of shaft and hub tapers.
4. Residual casting stresses.

Discussion of these suggested causes will be in the reverse order of their listing.

Residual Casting Stresses

The stresses in a casting due to shrinkage in cooling often increase, to a considerable extent, the stresses due to the operational load. The propeller manufacturer meets this problem by giving unusual care to the uniform cooling of the casting in the foundry, Commenting on this aspect of propeller manufacture Mr. A. J. Smith, Metallurgist and Assistant Foundry Superintendent, Bethlehem Steel Company, Shipbuilding Division, has said: (MODERN CASTING, Jan” 1959)

“Most propeller designs are conducive to good directional solidification as the hub section is tapered and cast with the large end up. The massive surface area of the blades … tends to dissipate heat rapidly and reduce time required for complete solidification of the casting.”

In addition to the fact that the propeller design lends itself to uniform cooling, and hence good directional solidification, the judicious use of external chills further controls the cooling. There is admittedly some possibility of hub cracking from residual casting stresses, but, because the propeller manufacturer is first and foremost a skilled foundryman, the possibility is remote and cracking from this cause must be considered the least important of the causes named.

Improper Fit of Shaft and Hub Tapers

When the fit of the tapers of a hub and shaft is once established there is little reason for this fit to be disturbed unless actual physical damage to either the hub or the shaft occurs. The fit of the hub and shaft, however, should never be taken for granted, for the possibility of physical damage to one or the other is all too great. It is to be recommended that a responsible representative of the owners or the shipyard make some positive check at each propeller change in order to assure the continued integrity of the fit.

This is particularly true if any damage has been sustained by the propeller shaft in or near the taper, or if for any reason the propeller has become loosened on the shaft; and it is equally true if, for reasons to be suggested below, the propeller hub bore has distorted. Under any of these conditions a thorough inspection of the propeller and shaft tapers should be made and remedial action should be taken before the vessel is released for return for service.

It should be pointed out that verifying the fit of the propeller and shaft is not a proper function of the propeller repair shop, but must be done at a time and place when the propeller can be actually fitted to the shaft on which it is used. Many, perhaps most, propeller repair shops do not have a full range of taper gauges, and there is little that these shops can do except to ascertain that the propeller bore is concentric at each end. Even so, any propeller repair shop can and should make a good visual inspection of the hub bore for any evidence of looseness, wear or uneven contact with the shaft. Such a visual inspection ought properly to be a part of the repair procedure, and any evidence of wear or uneven contact should be reported to the owners.

Improper Fit Of Key In Keyways

The improper fit of the key in the keyways is always a real cause of hub cracking, and for obvious reasons. If the propeller is forced over a key of improper size or one which does not fit squarely into each keyway forces of a large order will be applied to the hub bore. Even if the improper fit does not then produce hub cracking, the condition may cause a loosening of the propeller on the shaft with subsequent risk of damage to both tapers as well as excessive vibration in operation. As a result of careful investigation of numerous cracked hubs, it is the opinion of this writer that when a crack originates in the keyway it is almost certainly the result of improper key fit.

While not a part of this immediate problem, it should be noted that the use of filleted keyways can reduce the possibility of the kind of stress concentrations which have long been associated with the use of keyways with square-cut corners. This excellent practice deserves more wide-spread use.

Excessive Heating At Installation Or Removal

The most general cause of hub cracking is the application of excessive amounts of heat at the time of installation and removal of the propeller from the shaft. This stems almost entirely from the fact that the mechanics actually doing the job do not realize and have never been told how little heat is actually required to expand the propeller hub sufficiently for their purposes.

It seems likely that the actual cracking may occur in any one of three different ways. First, if excessive heat is locally applied it may cause uneven expansion and hence breakage. Second, excessive heat at installation may cause sufficient hub expansion to allow the hub to move too far forward on the taper with the result that the hub will cool at a point where shaft diameters are larger than those of the hub bore. Breakage, then, may well result. Third, the excessively hot hub may be quenched to hasten further work. This may readily cause cracking.

Cracking from excessive local application of heat is readily recognizable from the marked discoloration of the metal where the heat has been concentrated. In some extreme cases small areas will actually begin to melt. Cracking due to cooling and contraction of the hub after being allowed to move too far on the taper is much more difficult to recognize, and the location and nature of the crack may cause it to be confused with a crack caused by poor taper fits or even improper key fit.

Heating of the hub for removal, particularly of larger propellers, may be regarded as having some justification. The only real problem is that the heat be regulated and that persons entrusted with this task be instructed as to the amount of heat required to do the job. In this case the least amount of heat is usually the best amount. Heating the hub for installation, on the other hand, must be regarded as wholly unnecessary. There is nothing to justify this practice. A properly machined shaft and hub, when clean and free of any burrs, can be tightened to any acceptable standard by use of the shaft nut alone. When the hub is heated and shrunk on the shaft tremendous hoop stress results so that the hub is operating under a stressed condition that is wholly unwarranted and for which it was never designed. No propeller manufacturer can or will assume any liability under such circumstances and the vessel owner should realize that he indulges in the practice at his own risk.

Heating in shipyard is usually with the oxy-acetylene torch. The oxy-acetylene flame has a  temperature of very nearly 6000oF. Propeller metals melt at temperatures far below this. For example, manganese bronze melts at about 1800oF., while a typical austenitic stainless steel melts at slightly more than 2600oF. The amount of heat available in the oxy-acetylene flame is, therefore, far in excess of the needs and the greatest of care should therefore be exercised in its application. The use of a standard welding or cutting torch for heating should be avoided. Because of the nature of the welding or cutting tip the flame is tightly concentrated, and the result may be a localized application of an amount of heat far beyond the requirements for loosening the propeller on the shaft.

That extremely high temperatures are not required for loosening a propeller on the shaft is made evident by an examination of the expansion rates for various alloys. It should first be borne in mind that alloys expand relatively more in the temperature range up to 212oF. than they do at higher temperatures. The chart below indicates the relative expansion of a medium carbon low alloy steel, an austenitic stainless steel, a manganese bronze and a nickel-aluminum bronze.

Since the tolerance for the small end diameter of propeller hubs, as prescribed by the SAE standards, is only plus or minus one-thousandth of an inch, it can be seen that the hub need not be expanded more than a few thousandths of an inch to cause it to become loosened from the shaft. Because this paper has been intended to be nontechnical and non-mathematical no calculations of any kind are being submitted, but anyone desiring to do so may calculate the mechanical effects of heating by making use of the appropriate tables appearing in any of a great number of handbooks.

The above chart indicates that some alloys expand far more than others at the same temperature. This does not mean that the steel, for example, must be brought to a still higher temperature, for it can be readily shown that sufficient expansion of a propeller hub can be obtained within this temperature range. What it does mean is that mangenese bronze may require less heat to accomplish the desired expansion.

Recommendations and Conclusions

We know that whatever the desired temperature may be it cannot be produced uniformly over the entire surface of the hub merely by the application of heat from a torch. However, it is necessary to apply the heat as uniformly as circumstances permit, not allowing the torch to dwell over-long in any one place but being certain that it is passed from end to end of the hub and from one portion of the hub to another in succession. The surface temperature should not exceed about 200oF. for any propeller alloy.

Additional Considerations

No mention has been made of the possibility of hub cracking from impact. The nature of the propeller blade is such that it tends to absorb the greater part of the impact sustained by the propeller, and there is nothing in the literature of propeller design to indicate that the propeller hub is ever considered vulnerable to damage from impact alone.

There seems to be little value in increasing the hub diameter beyond some optimum which is generally considered to be about 15%. of the propeller diameter. Most propeller manufacturers do not recommend that the shaft diameter exceed 60%. of the hub diameter, although one nationally known manufacturer has used smaller hubs for years with excellent results. Not only are exceptionally large propeller hubs detrimental to performance in most cases, but it is a fact that the mechanical properties of most castings decrease as the section size increases. It must be concluded, therefore, that hub size has relatively little to do with hub cracking.

While some hub cracking can be sufficiently repaired as to give acceptable service life, the practice of hub repairing by any method now known to this writer is not to be recommended. The factors which argue against the practice are: residual welding stresses which cannot be properly relieved; distortion of the bore either from its opening up as a result of the crack, or because of warpage related to the welding. process; and, finally, the unfavorable ratio of repair cost to guaranteed service life. Hub repairs can be and are being made, and propellers with repaired hubs have been known to last indefinitely, but the fact still remains that such successful repairs are more often the result of a happy conjunction of events than the predictable skill of the operator making the repairs.

Conclusions and recommendations

From the foregoing discussion it can be seen that the principal causes of propeller hub cracking are excessive heating at installation and removal of the propeller, improper fit of the key in the keyways, improper fit of shaft and hub tapers and residual casting stresses. It has been shown that of these causes the most general and the most serious is that of excessive heating. It must be concluded that cracking for this reason continues only because mechanics doing the work do not know and have not been told how little heat is required. From these conclusions certain recommendations can be made which would divide the responsibility among the propeller manufacturer, the propeller repair shop, the shipyard and the propeller owner.

1. A propeller should never be heated for the purpose of installation. The propeller hub is not designed to be shrunk on the shaft and such practice is wholly unnecessary if the tapers are clean and free of burrs or irregularities.

2. The propeller key should never be allowed to bottom in the propeller keyway. It is a good rule to allow from .020″ to .030″ clearance between the key and the bottom of the propeller keyway. Keys should be made accordingly and owners should arrange for proper inspection of propeller keys and appropriate re-work when necessary.

3. The use of a propeller puller should become standard practice in every shipyard. Every propeller having a hub small end diameter of sufficient size to accommodate such bolts should be drilled and tapped for two puller bolt holes. Owners of propellers now in service should have those propellers drilled and tapped. Propeller manufacturers would be well advised to include such holes in new propellers, and to adopt standards for or at least recognize the relationship of bolt hole and propeller hub or shaft diameters.

4. Shipyards should thoroughly acquaint themselves with the implications of this problem and take such precautionary steps as may be necessary in the individual yard. The first step is to investigate current propeller removal practices in the light of this new knowledge of the problem and to provide such instruction as may be necessary to inform employees and to remedy any present unfavorable practices. The second step is to be certain that proper heating equipment – which would be available in almost every shipyard – is on the job site and in use for propeller removal. A third step is to encourage owners to have their propellers drilled for puller bolts and to show them that this small one-time cost will have long-range benefits. Finally, the shipyards should realize that the money spent for a strong hydraulic or mechanical universal puller will be the means of saving costly man-hours, and that the time and material involved in applying excessive amounts of heat can be saved.

5. Propeller repair shops should incorporate in their repair procedures a systematic visual inspection of the hub and bore of every propeller for any evidence of uneven contact or looseness on the shaft, for any evidence of bore distortion or lack of concentricity, and for evidence of physical damage to the bore or keyway which might prevent proper fit on the shaft at the next installation. Such shops should also inform owners of the benefits of using the bolt-type puller and encourage them to have their propellers drilled and tapped accordingly.

6. Owners should come to the realization that the fit of the propeller and shaft cannot be taken for granted. Regardless of the reliance of the owner on the judgment of either the shipyard or propeller repair shop, the fact remains that the ultimate responsibility rests with the owner or his representative to require that the necessary inspections be made and to require of the shipyard or propeller shop a report of their findings. When propeller shaft damage has been sustained the owner should require a precautionary re-fit of the shaft and propeller for his own protection – and he should be prepared to pay for the cost of such additional service. If the owner hauls his vessel at various yards and is not sure that proper puller equipment is available he should provide his own and carry it aboard.

It was the announced purpose of this paper to enumerate some of the more obvious causes of propeller hub cracking and to suggest certain precautionary practices which can be adopted by all concerned. If the paper has at all accomplished these ends then it can be counted as being of some slight value to the industry.

This paper has been prepared by L. L. WALKER, JR.
Houston, Texas,  as a service to the marine industry LL Walker, Jr. had one of the first, if not the first, propeller shop in Houston, TX. In early days he worked on airplane propellers. He was well respected in the marine business. He desired to contribute to the professionalism of the shipyards by offering advice on good installation practice. I found this paper in some old files, and it is as true today as it was when it was written. I do not know when that was, but my guess was about 1970. Mr LL Walker was also a member of The Rotary Club of Harrisburg and that club continues to meet every Tuesday. The name Harrisburg refers to the early city of Harrisburg TX. It is part of Houston TX now.

The illustrations and figures in this article are worth taking a few minutes to review. All are hand drawn. Every architect and ship fitter should be familiar with the technical names denoting ship lines, surfaces, and dimensions. Familiarity with these terms is essential in reading blue prints and in building and installing parts of a ship especially in older vessels.

SHELL —-The principal function of the shell is to act as a watertight skin. It also gives strength to the construction of intermediate parts.

TRANSVERSES —-These are the ribs or frames of the ship, and when placed in position, give the principal shape or contour, Transverses are not all the same distance apart; amidships, where there is the greatest strain, they are spaced more closely. The transverses are cut or notched where they connect on the shell, to allow the longitudinals to pass through. They are strengthened by clips at these points.

LONGITUDINALS —-These run fore and aft from bulkhead to bulkhead, except in the shelter and upper decks, where some are broken by hatch interference. They give strength and rigidity to the framework and shell. They are connected and welded at the flange of the channel to the shell or deck.

BULKHEADS —-The vertical partitions that divide the hull into separate compartments are called bulkheads. Some are watertight. These water-tight bulkheads are so arranged that in case of accident at sea, water would be confined to one compartment only. The collision bulkhead in the front end is constructed to withstand heavy strain and shock in case the bow be staved in.

DOUBLE BOTTOM —-The double bottom extends from the flat keel to the tank top. It is strongly constructed and is water tight so that in case of accident causing an inrush of water into the double bottom, the ship would still be able to keep afloat. The principal parts of the double bottom are the flat keel, vertical keel, floors, intercostal girders, bilge, brackets, tank top, longitudinals, bounding bars and angle clips.

OTHER PRINCIPAL PARTS —-From the tank top to the upper deck the principal parts are: bulkheads, pillars, deep tanks, bulk head stiffeners, girders, brackets, bounding angles, bar clips, shaft tunnel, engine settings, longitudinals, man-holes and covers

LINES DRAWING —-A plan showing, in three views, the moulded surface of the vessel. Fig. 7

MOULDED SURFACE —-The inside surface of the skin, or plating, of a ship. The moulded surface has no thickness, and is fair and smooth. Actually, when the ship has been built, the thickness of the plating will extend outside of the moulded surface. “Outside” strakes of plating do not touch the moulded surface if they have a liner against the shell frame. The heel of each shell frame is in this moulded surface (unless joggled). It should be remembered that this moulded surface is not an actual part of the ship. It is almost exactly the shape which a thin piece of sheet rubber would take if stretched tightly over the shell frames and main deck beams with no plating in place.  Fig. 1

BASE LINE —-A straight horizontal line at or near the bottom of the moulded surface from which vertical heights are measured. Usually, the base line is the very lowest part of the moulded surface. In is shown an exception.  Fig. 2

WATERLINE —-The intersection of the moulded surface with a horizontal plane at a given height above the base line. The six foot water line is exactly six feet higher than the base line.

These intersections are shown in the half breadth plan in the lines drawing. They should not be confused with the “load line” marked on the outside of a ship when built. Shipfitters use a waterline merely as a height above the base line and in this sense waterlines are marked on bulkheads, frames, and other members, for the purpose of properly setting and aligning the structure.

CENTER LINE —-A straight line running from bow to stern, midway between the sides of the ship. All transverse horizontal dimensions are taken from the center line. The center line as applied to a transverse bulkhead is a vertical line in the middle of the ship.

BUTTOCK —-The intersection of the moulded surface with a vertical plane at a given distance from the centerline of the ship. Buttocks are shown in the profile in the lines drawing. Shipfitters use a buttock merely as a distance from the centerline. Thus, they have buttocks marked on bulkheads, decks, foundations, etc., for setting and alignment. The buttocks and the waterlines which are marked on the steel members for regulating and setting are usually of some dimension expressed in even feet. That is, they would mark the 10’0″ W. L. (waterline ) and the 24’0″ Btk. (buttock) rather than a 10’7″ W.L. or a 23’6″ Btk.

FRAME LINE —-The intersection of the moulded surface with a vertical plane perpendicular to the centerline (transverse plane). Frame lines are shown in the body plan of the lines drawing. They get their name from the fact that shell “frames” or ribs usually are made to this shape and installed transversely in the ship. The lines drawing consists of three views; a half-breadth plan, a profile view, and a body plan (See Fig. 7). These views each show only one side of the ship (usually, the port side), because all dimensions for the starboard are equal and to the opposite ‘hand’; that is, the ship is symmetrical about the center line.

PROFILE —- A view looking at the moulded lines from starboard to port. The waterlines and the frame lines are straight when observed from this direction. The deck line, or “sheer” curve shows up clearly in the profile, which for this reason is sometimes called the sheer plan.  Fig. 4

BODY PLAN —- A view showing the shapes of the frame lines. The body plan is made in two parts. The right-hand part is a view looking directly aft at the for’d port side of moulded surface, while the. left-hand part is a view looking directly forward at the after half of the port side. This arrangement prevents the frame lines at the after end from obliterating or fouling the frame lines at the forward end. This view shows buttocks and waterlines straight, while the frame lines appear in their true shape.

HALF-BREADTH or WATERLINE PLAN —- A view looking down on the moulded surface. Here the frame lines and buttocks appear straight, while the waterlines show their true shape. To save space, only the port side is shown.

LOAD WATERLINE (L.W.L.) —- The waterline at which the ship will float when loaded to its designed draft.

FORWARD PERPENDICULAR (F.P.) —- A vertical line at the point where the load waterline crosses the foremost part of the moulded surface.

AFTER PERPENDICULAR (A.P.) —- A vertical line usually at the after end of the rudder post. If there is no rudder post, it usually is taken at the center of the rudder stock.

LENGTH BETWEEN PERPENDICULARS (L.B.P.) —- The distance from the forward perpendicular to the after perpendicular. To the designers, this length is very important, since upon it largely depends the amount of power needed to drive the ship.

LENGTH OVER ALL (L.O.A.) —- The total length of the ship from one end to the other, including bow and stern overhangs.

MIDSHIP SECTION —- A transverse section exactly half way between the Forward Post and the After Post Almost invariably, this is the widest part of the ship.

PARALLEL MIDDLE BODY —- The straight part at the center of the ship where the water lines and buttocks have no curvature; that is, where all the fore and aft lines are parallel.

DEADRISE —- The rise of bottom. It is the difference in height between the base line and the point where the straight line through the bottom flat surface intersects the vertical line through the side of the moulded surface at its widest point. (See A and B in Fig. 1; also, Fig. 3

BEAM — The width of-the ship (moulded surface) at the widest point. (See Fig. 3)

DEPTH —- The height of the ship ar the midship section from the base line to the moulded line of the deck at side (underneath).

DRAFT (Moulded) —- The height from the base line to the load water line.

FREEBOARD (Moulded) —- The difference between the moulded depth and the moulded draft. (It is the height of the side of the vessel which is above the water when she floats at her load water line).

CAMBER —- The curvature of the deck transversely. It is measured by the difference in height between the deck at center and the deck at side.

TUMBLE HOME —- The amount the top of the side shell slopes back toward the centerline between the point of widest breadth and the deck at side (see Fig. 3)

SHEER —- The curvature of the deck at side as shown in the profile. The amount of sheer forward is the difference in height between the deck line (at side) amidships and the deck line at the forward end (Fig. 4) The amount of sheer aft is the difference in height between the deck (at side) amidships and the deck at the after end. The line of the deck at center, in the profile, is higher than the line of the deck at side, owing to the camber, or transverse curvature of the deck. In Fig. 4 is illustrated the difference between the deck at the side and the deck at the center, owing to camber. The camber curve, as usually designed, is a circle of very large radius, but sometimes it is made as a series of straight lines, as in Fig. 5. The camber curve is the moulded line of the deck.

MIDSHIP SECTION AND OFFSETS —-The midship section of a ship, as stated before, is a transverse section taken halfway between the forward perpendicular and after perpendicular.  Fig. 6 shows the midship section of a type of oil tanker, giving the outline of the moulded surface at this section and also the spacing of the shell longitudinals and the longitudinal stiffeners. The camber of the deck is shown, as well as the deadrise and the bilge radius. This shape and spacing applies throughout the parallel middle body of the vessel (in this example, from frame 26 to frame 44, Table X) As illustrated, the shell longitudinals are three feet apart except for one space at the top of the side shell and four spaces in the bilge. The longitudinal bulkhead stiffeners are three feet apart except for three spaces at the bottom. The deadrise is nine inches. The moulded beam is seventy feet. The moulded depth is forty feet. The bilge radius is six feet. The camber of the deck is 1’5″ in straight lines. There is no tumble home. The stiffeners (longitudinals) heel inboard on the bottom shell and upward on the side shell and longitudinal bulkhead. In Fig. 7 are given the midship section offsets for this tanker. Offsets are measurements of distance from the base line or from the center line to any point in the moulded surface. Half-breadths are measured transversely from the centerline. Heights are measured vertically from the base line. From the table of half breadths, we see that at frame 26, the 8 foot waterline is exactly 35 feet from the centerline. The 2 foot waterline is only 32′ 9-3/4″ from the centerline at this frame. (The offset 32-9-6 means 32 feet – 9 inches – 6 eighths of an inch or 32 feet 9-3/4″). From the table of heights, we see that at frame 44 the four foot buttock is only 5/8 of an inch above the base line, and the 24 foot buttock is 6-1/8 inches above the base line. These midship section offsets apply from frame 26 to frame 44, which is the extent of the parallel middle body. Table X shows the offsets for the tugboat whose lines are illustrated in Fig. 7. At each frame station are tabulated the half-breadths for the 2-foot, 4-foot, 6-foot, 8-foot, l0-foot and 12-foot waterlines, and also for the deck at side. The heights of the 3’6″ and 7’0″ buttocks are also given for each frame station from #0 to #10. The table of offsets for an ordinary cargo ship or tanker consists of many pages and usually includes the following items: profile, frame spacing, midship section, camber curves, stem and stern profile, rail profile, detail of frames at bossing, half-breaths, heights, and sight edges. Sight edges are the longitudinal edges of shell (or deck) plates which are visible on the outside of the hull. It should be remembered that in practically all ships. the frame spacing is different in different locations, and before taking any measurements a drawing should be consulted.

LOCATING FRAME LINE AT BULKHEAD —-When it becomes necessary to set a transverse bulkhead or other member by means of a frame line marked on the adjacent members, the frame line must first be determined at the bulkhead itself. Fig. 8 In other words, it must be found out whether the face side (smooth side) of the bulkhead is to be directly on the moulded line, or whether the stiffener side of the plating is to be on the moulded line. This information must be obtained from the drawings. No specific rule will cover all cases, and the frame line is sometimes on the forward side of the bulkhead, and sometimes on the after side. In case of a discrepancy between two drawings showing the same member (for instance if the shell drawing shows the bulkhead plating aft of the frame line, while the bulkhead drawing shows the plating thickness forward of the frame line) the shell plan shall be assumed correct for the purpose of setting the bulkhead.

CORRUGATED BULKHEADS —-In setting the more recently adopted type of corrugated bulkheads, as in Fig. 9, the drawing must be consulted for location of frame line. Here the moulded line may be on either the face side or the stiffener side of the bulkhead, at the extreme width of the web bulkhead stiffeners. In this type of corrugated bulkhead, the depth of the corrugations varies at different heights on the bulkhead. The deeper corrugations at the bottom supply the increased bulkhead stiffness which is required owing to greater pressure of water (or other liquid) in the lower part of the tank.

SCRIBING AT CORRUGATED BULKHEAD —-When it is necessary to scribe a large bracket or other plate to fit in the corrugations of a bulkhead, the following precautions must be taken to assure a neat fit. The bracket shown in Fig. 10 must be scribed off to move 2″ to the left. If there were no corrugations, this would be a simple matter of marking a vertical line on the bracket with a 2′ spacer to give the proper cut. This line would be similar to that shown at “a” and at “c” in Fig. 10. However, the sloping sides of the corrugations, as at “b” and “d” cannot be marked off with the same 2′ spacer, because the opening thus burned out would be too large. The measurements for scribing at the sloping surfaces (that is at “b” and “d”) must, therefore, be taken in a horizontal direction as shown.  Table XI

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Abaft —-Aft of; farther aft than.
Access Holes—- Holes cut in ship’s structure to permit entering or leaving various compartments.
Accommodation Ladder—- A portable set of steps on a ship’s side for the accommodation of people boarding from small boats or from a pier.
Aft —-Toward, at, or near stern.
After—– Nearer stern.
Aftermost—- Nearest the stern.
After Body—- Hull form aft of the midship section.
After Peak—- The compartment in the narrow part of the stern, aft of the last water-tight bulkhead.
After Peak Bulkhead —- Watertight bulkhead farthest aft.
After Perpendicular —-A vertical straight line at, or near the after edge of rudder post.
Air Hammer—- Hammer driven by compressed air for riveting, or chipping. Sometimes called an air gun or “gun.”
Air Port —-A circular opening or window through the ship’s, or deck house, for light or ventilation.
Amidships —-At or near the midship section of the ship.
Anchor —- A heavy hook-shaped device for holding a ship at rest in water. The anchor grips the ocean bottom and is fastened to the ship by a chain. There are a number of different types of anchors. Some of the different anchors are: Work boat anchors, Stockless, Hall, Mushroom, Eells, Kedge, Navy pattern, Union, and Speck.

Anchor Joining Link —-A chain member with a removeable part used to connect the anchor to the swivel on the chain assembly.

Angle Clip—- A short piece of angle bar.
Angle Collar —-A ring made of angle bar.
Anneal —-To soften metal by heating and allowing it to cool slowly.
Anode —-Zink or aluminum or some such alloy that is fixed to the hull of a vessel. They are ‘eaten’  up by electrical currents moving from the vessel to the water. The anode is sacrificed to protect the metal hull of the vessel – without the anode, the hull plating would be dissolved by electrolysis.
Aperture —-A recess in which the propeller is located.
Assemble —-To fit together small parts, in making a large section,or part .
Athwartship —-Across the ship at right angles to the centerline.
Auxiliaries —-Machinery supplementary to main propulsive units.
Awning Deck —-Shade deck above another deck.

Babbet —-A relatively soft metal alloy used for bearings.
Ballast —-Any weight or weights (usually sea water, but could be concrete, scrap steel, etc.) used to keep the ship from becoming “top heavy” or to change her trim. Some of the largest cannons in the navy were on hospital ships – they were in the bilge for ballast.
Ballast Tank —-Watertight compartment to hold ballast.
Barge —-A water tight vessel that floats in water. Cargo barges in the USA do not have propulsion.  Picture of 2 loaded inland rivers tank barges, carrying  liquid cargo. Some have tanks for carrying oils and chemicals, others have hoppers for dry cargoes like grain or just a flat deck for specialized cargo. In the USA oil and chemical tank barges must meet US Coast Guard rules and regulations. The plans must be approved prior to construction and all repairs must be approved by the USCG. They must be drydocked on a schedule for routine underwater inspection.
Barnacle —-Small marine growth which attaches itself to a vessel’s hull in large numbers, often greatly retarding her speed.
Battens —-Long strips of wood used in the mold loft for fairing lines; also, wooden protective strips in cargo holds; see hatch battens.
Beam —-An athwartship member supporting a portion of a deck. Also,the width of the ship.
Beam Knee —-(See Bracket)
Below —-Below a deck or decks (corresponding to “downstairs”).
Bend —To fasten; as, to  bend  on  a  rope
Bending Rolls —-Large machine used to give curvature to plates. Also see ‘press brake’.
Bending Slab—- Heavy cast iron perforated slabs arranged to form a large floor on which frames, etc., are bent.
Berth —-A place for a ship; a place to sleep; a bunk; also, a specified small section of the hull structure.
Between Decks —-The space between any two decks.
Bevel —-The angle between the flanges of a frame or other member.(When greater than a right angle, open bevel; when less, closed.) Also,to chamfer.
Bilge —-Curved section between the bottom and the side of a ship;the recess into which all water drains.
Bilge Blocks —-Supporting blocks used under bilge for support during construction or dry docking.
Bilge —-A fore and aft member fitted to the outside of the shell plating along the bilge, to prevent excessive rolling of the ship.
Bilge Pump —-Pump for removing bilge water.
Bilge Strake —-Course of plates at the bilge.
Bilge Water —-Water in ship due to leaks, sweat, etc.
Bilge Well —- A sump to which bilge water drains.
Binnacle —-A case, box, or stand containing a ship’s compass, adjusting magnets, and a lamp for use at night.
Bitt —-A vertical post used in making fast lines; a bollard.
Bitumastic —-An elastic cement used in place of paint to protect steel.
Boat Deck —-A deck on which lifeboats are kept.
Body Plan —-A drawing which shows frame lines in elevation.
Boiler —-Container in which water is heated to form steam.
Boiler Chocks —-Stay braces which prevent fore and aft movement of boilers.
Boiler Foundation —-A support for a boiler.
Bollard —-A single tie post (see bitt).
Booby Hatch —-A watertight covering over a deck opening, which is used for a stairway or ladder.
Boom —-A long, round, heavy spar, pivoted at one end, usually used for handling cargo, etc.
Boom Rest —-A support for a boom when the boom is not in use.
Boom Step —-A socket for end of boom.
Bosom Piece —-A short piece of angle riveted over a butt joint of two angles, a butt strap for angle bars; a splice piece.
Boss —-The curved swelling portion of the ship’s hull around the propeller shaft.
Boss Frame —-A hull frame which is bent for clearing propeller shaft tube boss
Boss Plate —-A shell plate covering the curved portion of hull where the propeller shaft passes outboard.
Bow —-The forward end of a vessel. (Usually the pointed end.)
Bowsprit –A spar projecting forward from the bow of a vessel used to attach sails and stays.
Bracket —-A triangular plate used to connect rigidly two or more parts, such as a deck beam to a frame, a frame to a margin plate, etc.
Braze —-To heat and join by means of hard solder (spelter). This may be brass, bronze, or other alloys.
Breakwater —-A braced guard plate which prevents solid water from sweeping the decks.
Breast Cap —-Small plate on top of bulwark, at stem of vessel to stiffen bulwark.
Breast Hook —-A triangular-shaped plate extending horizontally across the bow behind the stem, stiffening the stringers and stem.
Bridge, Navigating —-A deck from which the ship is navigated.
Bridge Deck —-A deck of the superstructure amidships.
Brow —-A watershed over an airport; a small inclined runway to allow passage of trucks over hatch coaming, or through bulkhead door, etc.; sometimes portable.
Buck frame —-In a double skin tank barge, these frames act as spacers in the void tanks. A 4’6″ wide void might have 2 vertical 8″ channel iron with 3″ x 3″ x 5/16″ angle iron between. Also called a transverse truss.
Building Slip —-A place where the ship is built; a shipway.
Bulb Angle —-An angle shape, which is reinforced at one toe.
Bulb Plate —-A narrow plate reinforced on one edge.
Bulb Tee —-A Tee bar with toe of web reinforced.
Bulkhead —-A vertical partition corresponding to the wall of a room, extending either athwartships or fore and aft. A steel partition in a ship.
Bulkhead Sluice —-A small opening in a watertight bulkhead which can be opened or closed from the deck above.
Bulwark —-The ship’s side above the weather deck.
Bull Riveting —-Driving rivets by squeezing them with a high powered air or hydraulic machine.
Bunker —-A compartment used for the stowage of coal or other fuel.
Buoyancy —-Ability to float; lifting power when immersed.
Butt —-The joint formed when two parts are placed edge to edge.
Buttock —-A distance from centerline; an intersection of moulded surface with a vertical longitudinal plane.
Butt Strap —-A small plate used to connect the two parts of a butt joint by overlapping each; a splice piece.
Butterworth (TM) Gun —-Butterworth is  the name of a company that manufactures automatic tank wash machines. The machines can be hose mounted or permanent. The water flowing through the machine causes the wash nozzles to turn. Gears inside the machine make the spray pattern ecentric so all the walls and floor is washed without moving the hose. (At least all that can be sprayed from the one piont.) The cycle time is adjustable although not necessarily in the field.
Butterworth Hatch —- An opening on the deck of a vessel opened when cleaning or ventilating the tanks. May be round or square, secured by bolts or dogs.
Button —-A cast or fabricated deck item, usually round, that is used to thread cables between vessels when they are made-up.

Caboose —-A kitchen on deck.
Camber —-The athwartship rise or crown of a deck.
Cant Frame —-A frame which is not square to the keel line.
Capstan —-A revolving drum, with vertical axis, used for heaving in lines.
Cargo —-The freight carried by a ship.
Cargo Battens —-Strips of wood used to keep cargo away from the steel hull.
Cargo Boom —-A heavy boom used in handling cargo.
Cargo Hatch —-A large opening in a deck which permits the loading of cargo into holds.
Cargo Port —-An opening in a ship’s side used in loading and unloading cargo.
Casing Bulkheads —-Walls enclosing portion of vessel, as the boiler room casing. Also a covering for parts of machinery.
Cat’s paw —-A light puff of wind.
Caulk —-To make a joint watertight. The old saying  ‘the devil to pay and a half bucket of pitch’ referred to a very big joint to be caulked (pay) with the pitch and there may not be enough pitch.
Caulker —-One who caulks.
Ceiling Wood —-Sheathing on the tank top, sides of ship, and bulkheads; used to protect cargo.
Center Keelson —-(See vertical keel).
Center Line —-The middle line of the ship, extending from stem to stern .
Chafing Plate —-A bent plate used in minimizing chafing of ropes,as at hatches.
Chain Locker —-A compartment in the forward portion of ship in which anchor chain is stowed.
Chain Pipe —-A pipe for passage of anchor chain from deck to chain locker.
Chain Riveting —-Two or more rows of rivets spaces so that the rivets in one row are opposite those in an adjacent row.
Chain Stopper —-A device which prevents anchor chain from running out. It is moved into position after the anchor has been dropped.
Chamfer —-To cut off the sharp edge of a 90o corner. To trim to an acute angle.
Channel Iron —-A steel shape commonly used in vessel construction.
Chart Room —-A small room adjacent to the Pilot House in which charts and navigating instruments are located.
Chock —-A heavy fitting through which ropes or hawsers may be led.A saddle or seat of wood or metal.
Chock-Boat —-A cradle or support for a lifeboat.
Chock-Roller —-A chock with a sheave to prevent chafing of ropes.
Cleat —-A fitting having two arms or horns around which ropes may be made fast. Also called a kevel. A clip on the frames of a ship used to hold cargo battens in place.
Clinching Pan —-A flat plate for clinching nails. (Used in the mold loft.)
Coaming —-The vertical boundary of a hatch or skylight.
Cofferdam —-A narrow vacant space between two bulkheads. A double watertight bulkhead.
Collar —-A flanged band or ring. A welded plate used to close a frame or beam penetration through plating.
Collision Bulkhead —-The watertight bulkhead nearest the bow of a ship; forepeak bulkhead.
Companionway —-A covered stairway leading downward from an open deck. A series of steps leading from the deck to a cabin or saloon below; also, the space occupied by these steps.
Compartment —-A subdivision of space or room in a ship.
Corrugated —-Having a series of wrinkles or grooves arranged so as to produce stiffness.
Corrugated Bulkheads —-Bulkheads with corrugated plating, eliminating the need for many welded stiffeners.
Counter —-Overhang of the stern of a ship.
Countersink —-To taper a hole for a flush rivet or bolt.
Cowl —-The hood-shaped top of a ventilator pipe.
Cradle —-A form on which bows, etc., are assembled. The support in which a ship rests during launching; a launching cradle.
Cross header —-A pipeline that crosses over a tank providing a transit for cargo without tying into the vessel.
Cyclodial propulsion system —-A system of vertical blades that have taken the place of propellers for propulsion in some applications. Made by Voith Hydro GmbH & Co.. Generically referred to as a “tractor system”.
Cutless  Bearing —-A rubber bearing used to steady the propeller shaft in the water. It usually has longitudinal groves to catch water which then acts as a lubricant. The rubber is fused to a brass tube. The brass tube is pressed into a steel tube or cylinder and the steel is welded to the vessel hull. The fits and alignment have to be exact for these items.

Davit —-A crane arm used in handling small boats, lifeboats, stores, gear, etc.
Dead Flat —-A portion of a ship’s side or bottom where the plating has no curvature; also, the midship portion of constant cross section.(The parallel middle body.)
Dead Man —-A buried timber (etc.) that has an attached pipe or cable going to the surface for the purpose of securing a vessel at a dock or along a riverbank.
Dead Rise —-The rise or upward slant of the bottom of a ship from the keel to the bilge.
Dead weight—-The total weight of cargo, fuel, water, stores, passengers and crew, and their effects, which a ship can carry.
Deck —-A part of a ship corresponding to the floor of a building.
Deck-House —-A shelter built on deck.
Declivity —-Inclination of shipways to provide for launching.
Deep Tank —-A deep compartment usually extending from tank top to lower deck.
Derrick —-A device for hoisting heavy weights, cargo, etc.
Die —-A tool for forming a rivet head (applied to rivet dies).
Displacement —-The total weight of the ship when afloat, including everything on board, (equals weight of water displaced.) Usually expressed in long tons.
Dog —-A small bent metal fitting used in closing doors, hatch covers, manhole covers, etc.; a bent bar of round iron used in holding shapes on bending slab; any small flat lug temporarily welded to structure as backing for a wedge.
Dolly Bar —-A heavy bar to hold against a rivet, to give backing when riveting.
Double Bottom —-Compartments at bottom of ship between inner and outer bottoms, used for ballast tanks, water, fuel,oil, etc.
Doubling Plate —-A plate fitted outside or inside of another to give extra strength or stiffness.
Drag —-The amount the stern end of the keel is below the bow end when the ship is afloat, but not on an even keel.
Draft —-The vertical distance of the lowest point of the ship below the surface of the water, when afloat.
Draft marks are the painted numbers on the side of a vessel. The numerals are 6″ tall and are placed on the side shell so the bottom of the numeral is at the indicated depth. For instance, if a 1′ numeral is placed, then the bottom of the numeral is the 1′ mark and the top of the numeral is at the 1′ 6″ mark.
Drift Pin —-A small tapered tool used in aligning holes in adjacent members.
Drop Strake —-A strake discontinued near the bow or stern.
Drydock —-A watertight vessel fitted with pumps and valves usually built in a u-shape. The valves are opened, the vessel sinks, the vessel to be docked is pulled over the drydock deck, the valves are closed and the pumps are started, as the drydock becomes more buoyant, drydocking the vessel to be repaired.

Erecting —-The process of hoisting into place and bolting the various parts of a ship’s hull.
Even Keel —-A ship is said to be on an even keel when the keel is level or parallel to the surface of the water.
Expansion Trunk —-Raised portion of tank used on some oil tankers to allow for the expansion of oil when temperature changes.
Eye Bolt —-Bolt whose head is in the form of a ring or eye.

Fabricate —-To make assemblies from ‘raw’ material.
Face Plate —-A narrow stiffening plate welded alone the edge of any web frame or stiffener.
Fairing or Fairing Up —-Correcting or fairing up a ship’s lines or structural members; assembling the parts of ship so that they will be fair,that is, without kinks, bumps, or waves.
Fairlead —-A fitting through or over which a rope, line, etc., maybe led so as to change its direction without excessive friction.
Fairwater —-Plate or casting used to preserve streamline flow of water past the hull structure or propeller hub.
Fathom —-Six feet. 120 fathoms = 1 cable.  6,085 feet = 1 nautical mile
Fathometer —-A device to measure the depth of water, by timing the travel of a sound wave from the ship to the ocean bottom and return.
Faying Surface —-The contact surface between two adjoining parts.
Fender —-A portable device to protect a ship when bumping a pier;sometimes made of wood, rope, etc.; permanently installed extension which protects the hull of a ship in docking.
Fidley —-Casing top over boiler room.
Fidley Hutch —-A hatch over boiler room.
Figurehead – The bust, often of a woman, on the bow of a vessel, just under the bowsprit.
Flagstaff —-Flagpole at stern of ship; ensign staff.
Flange —-A part of a plate or shape at, or nearly at, right angles to main port; to bend over to form an angle.
Flare —-The sudden widening of the shell at top near the bow.
Flat —-A small partial deck (built level) without curvature.
Floor —-The lower portion of a transverse frame, usually a vertical plate extending from center line to bilge, and from inner to outer bottom.
Flotsam —-Floating objects or debris in the water – wreckage that floats after a vessel sinks.
Fore and Aft —-In line with the length of the ship, longitudinally.
Fore and Aft Gangway —-A walkway between deck houses at or near centerline of ship.
Forebody —-A hull form forward of the midship section.
Forecastle —-The forward upper portion of the hull, sometimes used for the crew’s quarters.
Forefoot —-The part of the keel which curves and rises to meet the Stem.
Forepeak —-The large compartment or tank, at the bow in the lower part of the ship.
Forepeak Bulkhead —-Collision bulkhead; bulkhead nearest bow.
Forging —-Steel worked to special shape by hammering while red hot.
Forward—-Near, at, or toward, the bow of the ship.
Forward Perpendicular —-A vertical line through the intersection of the stem with the load water line.
Foundations —-Supports for boilers, engines, and auxiliary machinery.
Foundations, Auxiliary —-Supports for small machinery, such as winches, condensers, heaters, etc.
Frames —-Ribs forming the skeleton of a ship.
Frames —-Continuous Frames combining side frames and floors.
Frame, Side —-Frame inside a ship, above and connecting to margin plate or floor plates.
Frame Spacing —-The fore and aft distance between adjacent frames.
Frame, Web —-A heavy side or continuous frame, made with web plate for extra stiffness.
Freeboard —-The vertical distance from the upper watertight deck to waterline, when the ship is fully loaded.
Freeboard Mark —-(See Plimsoll mark.)
Freeing Port —-Hole through bulwark which provides ready drainage of water from deck.
Funnel —-A smokestack of a vessel.
Furnace —-A heater or large forge for heating plates or shapes for bending; to bend by heating in furnace.

Gaf Spar —-The honored place on a ship flag pole for the stars and stripes. All other flags fly at a lower place.
Galley —-A cook room or kitchen.
Galley Dresser —-A cook’s work table.
Galvanizing —-Coating metal parts with zinc for protection from rust.
Gangway —-A passageway, a ladder, or other means of boarding a ship.
Garboard Strake —-The course of plates next to the keel of a ship.
Gasket —-Packing of canvas composition, or other material, used in making a joint that does not leak. Composition gaskets may have used asbestos. Since the awareness of asbestos as a health problem, asbestos is not often used. Gaskets may be rubber, composition, spiral wound with metal and composition, etc. O-rings are a type of gasket.
Girder —-Fore and aft stiffening member for deck or bottom shell.
Girth —-Any expanded length.
Grab Rods —-Bent rods welded to bulkheads or ship’s side to form a ladder.
Grating —-Light platform or walkway built up of metal bars, used for access to machinery.
Graving Dock —-A arrangement for getting vessels out of the water so that bottom work can be done. Usually a slip is dug in the shore, a vessel is floated in, a wall is placed across the open end of the slip and the water is pumped out of the ‘tank’. Often used for very heavy objects.
Grommet —-A soft ring used under a nut or bolt head to maintain water tightness.
Ground Ways —-Timbers secured to the ground, under the hull on each side of the keel, on which a ship is launched.
Gudgeons —-Bosses on stern post drilled for pins (Pintles) on which rudder swings.
Gunwale —-The junction of deck and shell at top of sheer strake. Pronounced ‘gunnel’
Gunwale Bar —-Angle iron which connects stringer plate and shell plates. (Riveted work)
Gyro-Compass —-A mechanical compass operated by means of a gyroscope. This compass indicated true north rather than magnetic north.
Gyro-Repeater —-An apparatus to show the reading of the gyro compass at a distance from the main gyroscope equipment.

Halliard —-A line for raising or lowering a sail or a flag.
Hatch —-An opening in a deck for passage of cargo, etc.
Hatch Battens —-Flat bars which are wedged against hatch coamings to secure tarpaulins.
Hatch Beam —-A portable beam used to support wooden hatch covers.
Hawse Pipe —-Casting, or castings, through deck and side of ship at bow for passage of anchor chain.
Hawser —-A large rope used in towing or mooring.
Headlog —-The bow plate on a vessel that is made of thick steel plate.
Heeling —-The inclination of a vessel to one side.
Hogging —-Straining of the ship which tends to make the bow and stern lower than the middle portion. This is the opposite of sagging.
Hog Wire —-On early vessels and river boats the problem of hogging was solved to some extent by putting a wire from the bow and stern to the top of a mast in the middle of the vessel. That caused the bow and stern to lift and helped reduce hogging.
Hold —-The inside of a hull; cargo space.
Hold Beams —-Structural members placed in a hold, similar to deck beams, but having no plating or planking on them.
Holder-On —-One who “backs up” or “holds on” the head of a rivet while the point is being “driven”, or upset.
Horn —-To line or square-up; also, part of a cleat.
Hull —-The body of a ship, including shell plating, framing, decks,bulkheads.

I-Beam —-A structural shape with cross section resembling the letter I.
Inboard —-Inside the ship; toward or nearer the center line.
Inboard Profile —-A drawing of the longitudinal section at centerline of ship.
Inert Gas —-A gas such as carbon dioxide or nitrogen that is used to make an oxygen deficient atmosphere. Inerted tanks are useful for preserving cargo integrity and reducing the explosive potential of cargo tanks.
Inerted —-Implies that a tank is filled with an inert gas.
Innage —- A measurement of liquid cargo in a tank. It is the distance from the top of the cargo to the bottom of the tank. It is the opposite of ullage.
Inner Bottom —-Plating forming the upper surface of the double bottom. Also called tank top.
Inner Shell —-A plated surface or “shell” inside the outer shell plating, used as additional protection in case of collision or other accidents.The space between the inner and outer shells is often used as a storage space for liquid ballast or cargo.
Inserted Packing Red lead —-soaked canvas strips placed between connections that cannot be caulked successfully; stop waters.
Intercostal —-Made in separate parts; between frames, beams, etc.,the opposite of continuous. (Floors are continuous; longitudinal girders are intercostal in most cargo vessels.)
Isherwood System —-A system of building ships in which the main framing is longitudinal or fore and aft, instead of transverse as in ordinary ships.

Jack Staff —-A flag staff at the bow of a ship.
Jetsam —-Items that are thrown overboard from a vessel in distress.Discarded cargo that washes ashore.
Joggle —-An abrupt bend or offset in a plate, bar, or frame to eliminate the use of liners.
Jumbo  Barge —-Refers to a barge size. The original wood river barge, was finally standardized at 26′ x 110′ long. That size was determined to be too small and so a new larger size called a ‘jumbo’ was developed and it is 195′ x 35′. The jumbo is sized to fit in a lock with a tow of barges and a tow boat. Inland rivers are supposed to accommodate 12′ of water depth for navigation. The jumbo barges have sides that are about 14′ tall so they can be loaded to 12′ depth and still have some freeboard.

Keel —-The principal fore and aft member of a ship’s frame. The keel runs along the bottom, connecting the stem and stern, and to it are attached the frames of the ship.
Keel-blocks —-Heavy blocks which support the keel of the ship during construction or while on drydock.
Keel, Flat —-The bottom shell strake on centerline of ship.
Keelson, Side —-Fore and aft member placed on either side of, and similar to, the vertical keel.
Keel, Vertical —-Vertical plate used as reinforcement for keel, often called center-keelson.
Kenter Joining Shackle —-A fitting on the vessel anchor chain to connect the swivel to the chain.
Kevel —-A deck fitting used to secure a line or a cable to a vessel
King Post —-A stub mast, outboard from center line, used to carry cargo booms; king posts also serve as ventilators.
Knot —-A tie in a line (for instance a square knot). A nautical mile. (About one and one-seventh statute miles.)
Knuckle Plate —-A plate bent to form a knuckle. A knuckle is a rounded corner usually found on the bottom of a vessel. It is believed that if a vessel contacts the river bank, a vessel with rounded ‘knuckle’ plates can be dislodged easier than one that has sharp corners.
Kort Nozzles —-A steel tube that surrounds a propeller, directing the water and improving efficiency.

Ladder —-Inclined steps, used aboard ship in place of “stairs.”
Lap —-A joint in which one part overlaps the other, thus avoiding the use of a butt strap; also, the amount of overlap.
Larboard —-The original name for the left side – the port side. Too much confustion with starboard and it had to be changed.
Launching —-The operation of placing a hull in the water by allowing it to slide down on greased skids, called launching ways.
Laying Out —-Marking plates or shapes, for shearing, punching, etc.
Lazarette —-Ship’s storeroom between decks.
Left Side of A Vessel —-Today the left side is the Port side. As a memory aid, remember that port wine is red and so left is red. Starboard is green and it is the right side. But it hasn’t always been that way. Port used to be ‘larboard’. However there was too much confusion with the word starboard and it was changed to port.

Left step —- Sailors were superstitious and it was considered to be bad luck to make the first step on deck with the right foot.
Left Length Between Perpendiculars—-The length of a ship measured from the forward perpendicular to the after perpendicular.
Length Over All —-The length of a ship measured from the extreme forward end to the aftermost point of the stern.
Lift —-To make a template from measurements taken from the job.
Lightening Hole —-A hole cut in a member to reduce its weight.
Limber Hole —-A small hole cut in a plate near the bottom to permit the passage of water or cargo.
Liner —-A flat or tapered strip of steel placed under a plate or shape to bring the member in line with another which it overlaps. A filler.
Lines —-The form of a ship as represented by its moulded surface.
List —-To lean over to one side.
Load Waterline —-Line of surface of water on a ship when loaded to designed draft.
Loftsman —-A workman in the mold loft, who lays down ship lines and makes templates.
Longitudinal —-A shell, deck, or bulkhead stiffener running fore and aft.
Lug Pad —A projection on deck with hole for fastening a block flora lead.

Main Deck —-Usually the deck immediately below the shelter or weather deck.
Manhole —-A hole cut in a bulkhead, tank top, etc., to allow the passage of a man.
Margin Plate —-The outboard row of plates of the inner bottom, connecting to the shell plating to the bilge.
Marlinspike —-A pointed tapering tool which is used in separating strands of rope or cable in splicing.
Mast —-A large long spar, placed nearly vertical on the center line of a ship.
Mess Room —-A dining room for officers or crew.
Midship —-At or near the middle point of a ship’s length.
Midship Section —-A cross section through the ship, midway between the forward and after perpendiculars.
Mold Loft —-A shed or building with large, smooth floor on which the lines of a ship can be drawn to full scale.
Mooring —-Securing a ship in position by several lines or cables,so that she cannot move or swing; anchoring.
Mooring Pipe —-A casting which prevents chafing of mooring lines passing through bulwark plating.
Mould or Mold —-A light pattern of a part of a ship usually made of thin wood or paper. Also called a template.

Nautical mile —-6,085 feet (6 feet = 1 fathom) (120 fathoms = 1 cable)
Net Tonnage —-A figure obtained by making deduction from the gross tonnage for space not available for carrying cargo.

Oakum —-Untwisted fibers of old rope treated with a composition of resin and pitch, used to fill seams of wooden decks.
Offset —-To move out of line or position.
Offsets —-A table of moulded dimensions for waterlines, decks, etc.
Oil Tight —-Sealed by welding or caulking to prevent oil leakage. Steel barges are welded and tested to be air tight. Tank barges are inspected and tested to confirm that they do not leak. When oil or chemical barge hulls are repaired the USCG sends an inspector to confirm that the repair is done properly and that the welds are air tight. To prove air tight, the hull is pressurized with compressed air and a soap mixture is applied to the outside. That is called an air-test.
Old Man —-A rig for holding a drilling machine.
On Board —-On or in the ship.
On Deck —-On the upper deck; in the open air.
Outboard —-Away from the centerline, towards the side of a ship.
Overboard —-Outside; over the side of a ship, into the water.
Overhang —-That portion of the hull which is over and unsupported by the water.
Oxter Plate —-Bent shell plate which fits around upper part of stern post; also called tuck plate.

Packing —-Material which is placed between plates or shapes to make them watertight; wooden blocks and wedges which support a ship on sliding ways; spacers.
Pad Eye —-An eye located on deck which is used for fastening cables or on the hull for hanging tires or an attachment for hanging a block and fall for lifting the propeller or rudder.
Painter —-A rope used to secure a boat to anything.
Painting a vessel hull —-Vessels must be removed from the water to apply coatings. This vessel is on a drydock.The painter is using an air-less paint system. The paint is under very high pressure (1,000 lbs or more). The coating protects the steel hull from corrosion.
Palm —-Flattened top portion of rudder stock (for bolted connection). Also, a flat surface at the end of a strut or stanchion.
Panama chock —-A steel casting used for line handling – from one vessel to another vessel or to the dock. Developed for use in the Panama canal(?).
Panting —-An in-and-out movement of plating; to pulsate or throb. Panting may be caused by the lift and fall of a ship in a seaway, or by engine vibration.
Pay —-To caulk a seam. ‘the devil to pay’ refers to caulking a really deep or otherwise difficult seam.
Peak —-A narrow compartment at either end of a vessel.
Pillar —-A vertical member or column which provides support to a deck girder. (Also termed a stanchion.)
Pilot House —-An enclosed place in which the main steering wheel,controls, engine room, telegraph, etc., are located. A wheel house.
Pintle —-A pin on which a rudder hinges.
Pitch —-Spacing; as of rivets or gear teeth. Also a tar based material used to seal planks on wood vessels.
Planking —-Wood covering for decks, etc.
Plating —-The plates of a hull, a deck, a bulkhead, etc.
Plimsoll Mark —-A mark placed on the ship’s side to indicate maximum allowable draft.
Pontoon Hatch Cover —-A steel box-shaped member sometimes used in place of hatch beams to close in a cargo hatch.
Poop —-The after, upper portion of the hull, often containing the steering gear.
Poop Deck —-The first deck above the shelter deck at after end of a vessel.
Port —-A harbor; or opening in the side of a ship. The left hand side of a ship (looking toward the bow.) Originally called larboard. Associated with the red marking light. (think – port wine is red, so port side has the red light)
Porthole —-A circular opening in the ship’s side such as a window(see airport).
Press break —-A hydraulic or mechanical device for bending and shaping steel plate. In shipyards the plate is usually shaped cold. Plates bent in a press may be referred to as ‘shaped’ or ‘flanged’ plate.
Profile —-A side elevation of a ship’s form.
Propeller —-A rotating device which drives a ship through the water. Also see cycloidal propulsion system See the Propeller page for propeller information.
Propeller Post —-The forward post of stern frame, which is bored for propeller shaft.
Propeller Shaft —-Rotating bar by means of which the engine turns the propeller.

Quarters —-Living or sleeping rooms.

Rabbet —-A depression or offset designed to take some other adjoining part; as for example, the rabbet in the stem to take the shell plating.
Rail —-The upper rounded edge of the bulwarks.
Railway —-An inclined slope fitted with railroad track. A carriage is lowered down the track into the water, the vessel is floated over the carriage and both are brought up the slope until the vessel is drawn out of the water. Requires a very stout winch to pull the carriage up the slope.
Rake —-Slope aft of a mast, king post or stack.
Reaming —-Enlarging a rivet hole by means of a revolving, cylindrical, slightly tapered tool with cutting edges running along its sides.
Reeve —-To pass the end  of a rope through a pulley, etc.
Reverse Frame —-An angle bar or other shape riveted to the inner edge of a transverse frame as reinforcement.
Ribband —-A fore and aft steel strip or heavy batten which is used to temporarily align the transverse frames after erection.
Rigging —-Ropes, wire ropes, lashings, masts, booms, etc.; also, the handling and placing on board the ship of heavy weights and machinery.
Rivet —-A short round metal connection used to fasten two or more members together by clinching after being heated red hot.
Rope —-A line that is attached to a bucket. Everything else on a sailing vessel is a line, not a rope. The halliard for instance is a line that raises the sail and the sheet is a line pulls in the boom.
Roll —-To impart curvature to a plate. Also, the motion of the ship from side to side, alternately raising and lowering each side of the deck.
Roller Chock —-(See Chock Roller.)
Rose Box —-A screen or strainer placed around the end of a bilge suction pipe.
Rudder —-A flat piece or structure of wood or metal attached upright to the sternpost (or in single screw-vessels,to the rudder post) of a vessel by hinges, or pintles and gudgeons, so that it can be turned, as by a tiller, causing the vessel’s head to turn in the same direction, because of the resistance offered to the water by the rudder.
Rudder Post —-After post of stern frame to which the rudder is hung. (Also called stern post.)
Rudder Stock —-The shank of a rudder which extends through shell upward to the steering engine.
Rudder Stop —-Lug to limit the swing of the rudder.

Sagging —-Straining of the ship which tends to make the middle portion lower than the bow and stern. This is the opposite of hogging.
Samson Post —-A heavy vertical post which supports cargo booms; king post.
Scantlings —-The dimensions of various shapes.
Scarf —-To thin out or taper a corner or edge of a plate or shape to make a lap. A joint in a stem, bar keel or stern frame.
Screen Bulkhead —-A bulkhead, usually placed between the engine room and boiler room, which is fire proof, dust proof, and gas tight.
Scupper —-A deck drain.
Scupper Pipe —-A pipe which drains water from scuppers throughout the side of a ship.
Scuttle —-A very small hatch; a manhole.
Sea Chest —-A compartment through which sea water is admitted or discharged.
Seam —-A riveted or welded plate edge connection. A riveted seam overlaps; welded seam may or may not overlap.
Serrated frame—-Sometimes pieces of an angle iron are cut to allow for ventilation, reduce weight or as a shortcut that saves material in the vessel construction. These cutouts may be spaced regularly – every few inches or so and the frame is called a serrated frame.
Set —-Metal mold or template for use on bending slab.
Set Iron —-A bar of soft iron used on bending slab to give shape of frames.
Shaft Alley —-A casing (large enough in which to walk), covering the propeller shaft and extending from engine room to after peak.
Shaft Tunnel —-(See Shaft Alley.)
Shape —-A bar of constant cross section, such as a channel, T-bar,angle bar, etc. Also, to impart curvature to a plate or other member.
Shear Line —-A line at which a shearing cut is to be made.
Shears —-A large machine for cutting plates and shapes.
Sheer —-Curvature of deck in a fore and aft direction as seen in profile.
Sheer Strake —-The top full course of side shell plating.
Sheet Line —-The line (not a rope) that pulls in the boom that has a sail attached. By controlling the sheet, the boom is adjusted to maximum efficiency for the conditions at hand.
Shell Expansion —-A plan showing details of all shell plating and shell longitudinals. (Longitudinals would appear only on tankers)
Shell Landings —-Points on the frames where the edges of shell plates are to be located.
Shell Plating —-The plates forming the outer skin of the hull.
Shelter Deck —-A continuous superstructure deck above the freeboard deck.
Shore —-A temporary brace or prop.
Side Thruster —-A propeller in a tube that is mounted through the hull. They are particularly handy for maneuvering by providing side thrust.
Sight Edges —-Visible edges of plating (outside shell and above decks.)
Skylight —-An opening in a deck to give air and light to the compartment below it.
Sliding Way —-That part of launching way which moves with the ship.
Slop Chute —-Chute for dumping garbage overboard.
Sounding Pipe —-Vertical pipe in oil or water tank used in measuring depth of liquid in tank.
Spar —-Long, round member such as mast or boom; part of rigging.
Stability —-The tendency of a ship to remain upright.
Staging —-Planks or scaffolding on which to stand when working on sides or under decks.
Stanchion —-A pillar or upright post.
Starboard —-The right hand side of a ship, looking forward. This is oriented with the green marking light.
Stay —-A guy line.
Stealer —-A plate extending into an adjoining strake as at the end of a drop strake.
Steering Gear —-Apparatus for controlling the rudder.
Stem —-Forging, casting, or plating forming extreme bow of ship and extending from keel to forecastle deck.
Step —-To set in place (as applied to a mast); also, a socket for the end of a must; a support for the fixed or “hinged” end of a boom.
Stern —-The after or back end of a vessel.
Stern Frame —-A large casting or forging attached to the after end of a hull to form the ship’s stern. It includes rudder post, propeller post, and aperture for the propeller.
Stern Tube —-A long bushing or bearing through the stern to support the end of a propeller shaft.
Stiffener —-An angle bar, T-bar, channel, etc., used to stiffen plating of a bulkhead or other member.
Stool —-A support for a propeller shaft bearing in the shaft alley.A foundation, etc.
Stop Water —-Canvas and red lead, or other material, fitted between two metal parts to make a watertight joint.
Stowage —-A support or fastening for any gear, as, anchor or boat stowage.
Strake —-A fore and aft course, or row, of shell or other plating
Stringer —-A fore and aft member used to give longitudinal strength. Depending on location, these are called hold stringers, bilge stringers,side stringers, etc.
Stringer Deck —-The strake of deck plating which contacts the shell.
Stringer Plate —-A deck plate at the outboard edge of deck connected to the shell of a ship with an angle or a welded joint.
Strong Back —-A supporting girder for a hatch cover; a rig used in straightening bent plates; a bar for locking cargo ports.
Strut —-A support for a propeller tail shaft (used on ships with more than one propeller).
Sump —-A depession or low place in a tank – especially a tank barge. The cargo pipeline is placed very near the bottom of the sump. The sump is placed so that liquid cargo drains into it when the vessel is discharged.
Super structure —-Deck houses, etc., which are located above shelter deck.
Swash Plate —-A baffle plate in a tank which prevents excessive surging of a liquid.
Swivel Assembly —-A intermediate ‘link’ on a anchor chain assembly that allows the chain to turn. It is connected to the anchor joining ling and the kenter.
Syncrolift (TM) —-A platform fitted with winches and anchor chain.The winches lower the platform into the water, the vessel is floated on and the platform is raised. Sometimes the vessel can be rolled to a repair station on railroad track.

Tail Shaft —-A short section of a propeller shaft extending through the stern tube and carrying the propeller.
Tank barge —-A vessel designed for carrying -usually- liquid cargo.Often has an engine and a pump to assist in transferring cargo, but does not have main propulsion equipment.
Tank Top —-The plating over the double bottom.
Tankerman —-The official USCG classification of the person that supervises the transfer of cargo between vessels or vessel and shore. There are different grades of expertise A, B, C, D and LFG -  relating to the degree of hazard in relation to fire.
Tee-bar —-A structural shape with cross section resembling the letter T.
Template —-A mold or pattern. Sometimes made of plywood or paper.
Thrust Bearing —-A bearing or block to resist end thrust. A bearing on propeller line shaft which relieves the engine from the driving force of the propeller.
Thwart —-A seat in a lifeboat. Something that runs transverse.
Tiller —-An arm, attached to rudder head, which operates the rudder.
Tow Boat —-A vessel generally used on inland rivers to push barges. The tow boat pushes a tow of barges and it has a flat bow to face up to the barges.
Tow Knee —-On a tow boat (so named because they push a bunch of barges called a ‘tow’) there are almost always 2 vertical supports for the barges to rest on. These are called tow knees and they have stairs built in for the crew to get to the barges.
Tractor propulsion —-A system of vertical blades used to propel a vessel in the water. Used on some harbor tugs and ferries. Made by Volith. Sometimes called a cyclonic system in reference to the way the blades are mounted under the hull, and the way they turn.
Transom —-The main frame at the rudder stock (cant frames usually radiate from the transom frame). The very last (most aft) plate on a welded vessel.
Transverse —-Athwartships; at right angles to the keel.
Transverse Frames —-Athwartship members forming the ship’s “ribs.”Also see Buck frame.
Travelift (TM) —-A device for lifting vessels out of the water. Has rubber tires and slings. The slings are lowered in the water, the vessels floated in and  lifted out of the water with cable winches. Once raised, the vessel can be moved to a station, blocked, etc. and the Travelift can return to the slip to move another vessel.
Trick —-A sailor’s duration of time in steering.
Trim —-To shift ballast; to cause a ship to change its position in the water; drag.
Trunk —-A small casing passing through a deck, such as is used for ladders or ventilation.
Tug Boat —-A relatively small vessel with a big engine used to 1/ assist ships when the ships are being docked  2/ tow barges by pulling them with a cable in the ocean. Tug boats have a pointed bow, but are not especially designed for speed. Tug boats can face up to a vessel to push it or they can pull with a cable or they can make up on a vessel on the side, refered to as being on the hip.
Tumble Home —-An inboard slant of a ship’s side above the bilge.

Ullage Hatch —- A small hinged opening on a tank for gaging or sampling cargo. The ullage is the distance from the top of this hatch to the top of the cargo. It is the ‘opposite’ of innage.
Uptake —-Connection between boilers and smokestack.

Vapor Header —-A pipeline connected to the top of a cargo tank that channels the displaced tank vapors to a shore side control system.
Vertical Keel —-A row of vertical plates extending along the center of the flat plate keel. It sometimes is called the center keelson.
Voice Tube —-A large (about 1″ to 1.5″ OD) speaking tube that goes from one operating station to another. Very effective. They would have a whistle so that – for instance- when the bridge wanted to call the engine room they would blow in the tube. The whistle would notify the personnel at the other end that they were wanted.
Void Tank —-A watertight space that does not carry ballast or cargo. For flotation.

Water Line —-Any one of certain lines of a ship parallel with (and at various heights above) the base line. In half-breadth plans the waterlines are smooth curves showing the shape of the ship; in profile plans they are projected as straight lines
Watertight —-So riveted, caulked, or welded as to prevent the passage of water.
Waterway —-A narrow passage along the edge of a deck for drainage. A gutter.
Ways —-Timbers, etc., on which a ship is built or launched. (See: Launching.)
Weather Deck —-A deck exposed to the weather.
Web —-The vertical portion of a beam, the thwartship portion of a frame, etc.
Web Frame —-A frame with a deep web.
Welding —-Fusing together two or more members with electric arc or by other means. Welding is a process that can be done with coated electrodes, called stick welding. Modern electrodes have a coating that vaporizes during the weld process. That vaporized gas drives oxygen out of the molten weld puddle allowing the metals to be joined without holes. There are other weld processes such as gas shield wire welding, etc.
Well —- A cofferdam or a sump in the double bottom.
Wheel —-Nickname for propeller; steering gear control.
Winch —-A small hoisting device; used in pulling lines or cables in handling cargo. Can be hand, air motor, electric, steam, engine, etc…powered.
Windlass —-A machine used to hoist the anchors by winding in the anchor chain.
Wind Scoop —-A device used to divert air into a compartment of a ship.

Zee-bar —-A structural shape with a cross section resembling the letter Z.

Return to the SHIPYARD page.

copyright 2009
Hilliard Emission Controls, Inc.

]]> http://www.purgit.com/shipyard-terms-and-definitions/feed/ 0 http://www.purgit.com/cylinders-and-inerting-with-nitrogen/ http://www.purgit.com/cylinders-and-inerting-with-nitrogen/#comments Fri, 05 Feb 2010 05:14:37 +0000 hhilliard http://www.purgit.com/?p=353 Handling and using high pressure cylinders should only be done by trained personnel.

Please note: Cylinders contain stored energy that can be very dangerous if not used properly.

Small requirements for nitrogen gas are best served with cylinders. A typical large cylinder (about 5′ tall) can hold about 230 cubic feet of nitrogen gas, as an example if it has 2,200 psi, that is to say, if it is full.  Pressure is the prime indicator to tell if a cylinder is full. Temperature is a factor, but not as important. Note: There are cylinders that are rated for much higher pressure, but they are unusual.

There are many sizes of high pressure cylinders, some small enough to carry under an arm and others that are mounted on 18 wheel trucks. The internal volume of the cylinder and the pressure of the gas (and to some extent the temperature) are the things that are important to determine the number of cubic feet of compressed gas. Cylinders have a very interesting quality – they will hold the pressure and volume virtually forever, regardless of time. Only the use of the gas or a leak is the only reduction. But the limited volume can be a problem.

Nitrogen 12 pack cylinders

For larger requirements, cylinders are put together in racks.

230 scf high pressure cylinder

The “racks” are steel frames with 6 or 12 cylinders clamped together feeding into a single manifold. They often use the 230 cu.ft gas cylinders. So 12 cylinders x 230 cuft = 2,760 cuft or 78 m3. The strong advantage of cylinders is that the nitrogen will stay in them for years. And it will always be ready to go in an instant (if the valves work). However, the cylinder owner usually charges demurage – a rental fee for the cylinders, and that can be expensive over time. That problem can be overcome by purchasing the cylinders.

Liquid nitrogen dewar

Another option for larger quantities is a dewer. Dewers can hold liquid nitrogen, argon, oxygen or CO2, etc. A 180 liter dewer may hold 140 cubic meters at 10 bar. The disadvantage of liquid nitrogen is that it is a perishable commodity. It will vaporize and escape from the dewars over a short period of time. It may all be gone in 3 weeks if the dewars are left in the hot sun. Dewers come in many sizes from the little 1 liter size that the dermatologist might use to 200 liters or larger.  Generally when the dewar is very large it is simply referred to as a liquid nitrogen tank or LN2 tank and it can hold thousands of gallons or liters.

Liquid nitrogen tank truck trailers can hold about 500,000 cubic feet, (about 5,000 gallons) and they are expensive to rent and the nitrogen is always escaping due to boil-off, approximately .2% to 5% per day depending on how good the insulation is. Usually they have relatively low pressure tanks, 25 psi is normal. They usually have a transfer pump to move the nitrogen into stationary tanks.

Liquid nitrogen tanks can be stationary on concrete pads (these are the big ones with thousands of gallons)  and they often have a lower loss rate than tank trucks, but they are always venting boil-off gas at about  .2% to 5% per day. It all depends on the vacuum in the vacuum jacket. They must have a very good vacuum to resist the heat and minimize boil off. Pressures can be from 30 psi to 225 psi in these tanks.

PURGIT ISO tank

ISO tanks can have very low leakage rates. .2% is not unusual. ISO tanks are used for specialized shipping of nitrogen, argon, oxygen and other specialized cryogenic and industrial chemicals.

In most cases, the word nitrogen can be replaced with argon, oxygen, or helium. Also carbon dioxide is shipped in cylinders, but CO2 is technically not a cryogenic liquid because it is not cold enough.

Important note: A specialized pressure reducing regulator is necessary to successfully get gas out of a high-pressure cylinder. Most cylinder valves are specific to the cylinder gas. Oxygen takes one particular thread, fuel gas another, nitrogen another and so on. A regulator must have the correct thread to fit the cylinder. Oxygen hoses, regulators, valves must never be used for other gases. The different threads have numbers for identification.

For instance, connection #510 is for fuel gas like propane or acetylene. It is also called a POL which, at one time stood, I believe, for Prest-O-Lite who was an early manufacturer.  Thread connection #240 & #660 is ammonia, #320 is for CO2,  #580 is for nitrogen or krypton or helium, #540 is oxygen, and the list goes on….

Oxygen is dangerous because almost everything is fuel to pure oxygen. If a hose or pipe has been used for a oil product and even a trace of hydrocarbon is present when pure oxygen is connected, it can ignite spontaneously, causing an explosion or fire.

When the big fabrication shops are using torches to cut thick steel, the torches use a mixture of oxygen and acetylene. When the cut has started it is sometimes possible to reduce or shut off the flow of acetylene and only use oxygen. Mixing oxygen with a fuel gas is extremely hazardous and will almost certainly result in explosion or fire owing to the rapid oxidization caused by the fuel-O2 mixture. Oxygen equipment must never be used in fuel gas and then back in oxygen without cleaning.

Nitrogen generator

An option to cylinder or liquid nitrogen is a nitrogen generator. They make nitrogen gas out of air. They are somewhat expensive to purchase and they require an air compressor, but they make nitrogen when you want it, and there is no expense or loss when they are turned off. They are particularly useful in remote areas. The by-product of making nitrogen gas is oxygen gas, and nitrogen generators can be reconfigured to make oxygen gas for use in hospitals and for industrial O2.

Tank Inerting The trick to tank inerting is the proper placement of the supply hose in relationship to the exit location. The gas should be supplied at one end of the tank and it should exit at the other end. Usually it is not that simple because very few tanks have connections on each end. Big tanks, even ones with reasonable connection locations may take 3 or more volumes of nitrogen gas to reduce oxygen to under 8%.

CO2 is much better for tank inerting because the CO2 molecule is heavy and inexpensive compared to other gases. It can displace lighter gases rather than diluting them. Inerting with nitrogen gas is dangerous for operators because of the chance of asphyxiation. A filter mask is NO GOOD where the vapor has reduced oxygen. If there is no oxygen then a filter mask is not appropriate. In the case of low oxygen then you must wear a supplied air mask. It is prohibited to work in tanks with less than 19.5% oxygen without supplied air. Supplied air can come from scuba tanks or from an air hose led in from the outside, but this is very dangerous work and must only be attempted by trained personnel.

Some rules for working around inert gases are:

NEVER enter a tank unless it has been tested for oxygen and has more than 19.5%. The most dangerous steel tanks are the ones that are dry and rusty. The rust can absorb the free oxygen thereby making an oxygen deficient atmosphere.  Oxygen meters can be purchased or rented from safety supply stores.

STAY OUT of tanks with low oxygen. Carbon filter masks are no good. Confirm that there is enough oxygen to breathe.

EVERY TIME ventilate every tank with large amounts of outside air using a forced air blower before entering. Other chemicals may be more of a danger than low oxygen.

NEVER interchange oxygen regulators or hoses, etc. with fuel gas equipment. Always read and understand the material safety data sheets for the gas.

EVERY TIME use an experienced person to handle high pressure cylinders.

Most tanks – even those that have manways or manholes will be ‘enclosed spaces’. There are many rules governing entry into enclosed spaces. If you are considering entering an enclosed space please read and understand the hazards and follow regulations.

PURGIT is a tank degassing contractor that uses condensers chilled with liquid nitrogen. We have experience degassing tanks and inerting tanks with nitrogen, carbon dioxide, etc.