US2412578A

US2412578A - Dry dock pontoon construction

Info

Publication number: US2412578A
Application number: US497784A
Authority: US
Inventors: Frederick R Harris
Original assignee: Individual
Current assignee: Individual
Priority date: 1943-08-07
Filing date: 1943-08-07
Publication date: 1946-12-17
Anticipated expiration: 1963-12-17

Description

VD126- 17, 1946. F. R. HARRISl DRYDOCK PONTOON CONSTRUCTION Filed Aug. ,'7, 1943 5 Sheets-Sheet l IN VEN TOR. i Frederic R; Harris v Dec. 17, T1946. F. R. HARRIS vDRYDOCK PONTOON CONSTRUCTION 5 Sheets-Sheet 2 Filed Aug. 7, 1945 ii L SPM Dec. 17, 1946. F, R, HARRls 2,412,578

DRYDOCK PONTOON CONSTRUCTION Filed Aug. '7, 1943 5 sheets-sheet 4 b NIMH HIL En IMM F uw i is INVENroR. Frederic Jrns Arron/wav Patented Dec. 17, 1946 UNITED STATES PATENT OFFICE 11 Claims.

This invention relates to the construction of hulls and especially pontoon hulls for floating dry docks.

An important object of the invention is to prov-ide an improved internal framework for a dry dock pontoon, comprisingA a novel and advantageous arrangement of bulkheads and cooperating trusses.

The floating dry dock, adapted to lift a ship out of Water and properly support it for repairs, has undergone much recent development in keeping with modern progress in the design of. ships. At rst amarine Vessel comprised a shell. internally braced by transverse frames, rigidly connected to a central keel, which eX- tended over the vessels entire length. Therefore, in a dock, the whole ship load couldk be supported on blocks directly under the keel, which was the strongest. part of the ship.` Bilge blocks were added at the sides merely toV balance the vessel on the keel blocks.

The keel was afterwards replaced by a shallow double bottom Which, however, did notin any substantial manner change the. docking conditions; and floating dry docks were: designed before to take the entire load on acentral row or track of blocks, which were still. of timber and bore the full weight of the vessel without crush- But at the present day there are both. commercial and naval vesselsofv suchk great size and weight that, even shoulda continuous keel track be provided.k the whole length of the dock, this track would have to be sobroadthat asubstantial portion of the ships bottom would be covered thereby and made. inaccessible to workmen The remedy for this. is a plurality of tracks orv rows of blocks, side by side on the floor of thev dock; and a structural design for the dock-4 that is economical in the amount of material' used, and yet firm enough to withstand all working stresses due to the vessels weight, and other forces.

In floating dry docks of` prior construction a rugged, central longitudinal bulkhead is usually included; with a considerable number of' transverse bulkheads. My invention contemplates several bulkheads for carrying and sharing the weight of the ship; and: both the ship load andthe buoyancy load are transmitted to said'bulkheads by a system of frame-trusses; andV thencet'o additional bulkheads which intersectY theirst, and complete the framework of the hullof: the dock. The result is great strength and. alargesaving in structural material.V

The invention will be described in. connection with a pontoon of a multiple-unit dry dock; that is, a dry dock that is made up of. a number of similar pontoons connected together side by side to form along dockfor supporting a ship; as set iorthin my application for patent on a Multipleunit floating dry dock, Serial No. 482,376, led April 9, 1943, noW Patent No. 2,37 9,904, dated July 10, 1945. But the invention is not limited to pontoons of multiple-unit docks, and some features of the invention relate to hull construction generally.

My invention' provides bulkheads arranged so as to extend crosswi'se of a ship in the entire dock, and placed someV distance apart, and a seriesof trusses containing K frames on both sides of; each of said bulkheads. Horizontal beam members-to resist compression extend fro'mside to side of the hull of the pontoon and unite the centers of the K frames inthe diierent trusses; and the frames at each side are further braced by beams. connecting their centers. Thus the trusses are stiffened in their various positions and, with their increased rigidity, are' able to support high compression loads. The span ofv the uprights in the trusses becomes half of that in a' prior floating dry dock. The horizontal beam members in their turn, being joined rigidly'together, willrv resist eifectively the outsidey water pressures on the' sides andends of the'ponto'on.

Also my invention rendersi it feasible to rely upon relatively few bulkheads tonv transmit inherent pontoon truss-bending stresses. The K frame. trusses which, at their ends are securedto some of the bulkheads, will, together' with the additional bulkheads and their plating between the. trusses, render the whole interior framework so strong and rigid that all liability of Warping andsimilar strains in thsbulkheadsis eliminated."

Also the trusses render the deck and bottom so rigid that the entire deck and` bottom: plating willv act as flanges' for girders, thewebs of 'which are formed by' they additional bulkheads; and buckling and other'distortionof deck and bottom plates .becomes impossible.

In addition, my invention-contemplates sufli cient additional reinforcement in the central part of the pontoon. hull-tov cooperateiwith the bulkheads and trusses in realizing the fullf aim of the invention.

Another feature of the' invention relates to a combination of bulkheadsand trusses within the pontoon by which loadszare transmitted to some bulkheads and. througlrthem. to.- additi'onal; bulkheads. In theembodiment: of thefnventionillusitrated, the trusses and the`v variousbulkheads 3 are all connected together to form a unitary structure inside the hull.

A more specic object of the invention is to transmit deck load and buoyancy loads through parallel K frame trusses to bulkheads at the opposite ends of the trusses, and from these bulkheads to additional bulkheads within the pontoon connected to and intersecting the first bulkheads.

A further feature of the construction is that the bulkheads are of a composite structure that is thicker at the places where each bulkhead meets another bulkhead extending in a transverse direction. This construction may comprise solid columns located where the planes of the bulkheads intersect, the respective bulkheads being made up of sections connected with the solid columns in such a way that the column Ais structurally a part of the composite bulkheads.

Dry dock pontoons made in accordance with this invention have a number of bulkheads with parallel trusses between and on each side of the latter, bulkheads at the opposite ends of the trusses and under the wing wall sections on the pontoon, and other trusses beyond the last named bulkheads and less closely spaced. In this way the greatest strength is concentrated under the portion of the pontoon deck that supports the ship, and less strength is needed adjacent the ends of the pontoon where smaller stresses are encountered.

Some features of the invention relate also to the connection of structural members 'and to special joints that are particularly suitable for welded connections in ship construction and other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

In the drawings, forming a part hereof, and in which like reference characters designate corresponding parts in all the views,

Figure l is an enlarged sectional view taken on the line iof Figure 2;

Figure 2 is a diagrammatic, top plan view of a pontoon hull for a multiple dry dock built in accordance with this invention;

Figure 3 is a perspective view of jointing elements used at certain joints of the framing;

Figure 4 is an enlarged detail view illustrating the connection of some of the structural members shown in Figure 1;

Figures 5 and 6 are two enlarged sectional views taken on the lines 5-5 and 6-6 respectively, of Figure 2 showing the construction of the side trusses;

Figure 7 is an enlarged, fragmentary perspective view taken in the vicinity of the line 'lf Figure 8; 1

Figure 8 is an enlarged, sectional view taken on the line 3-8 of Figure 2 showing the structure of the other trusses;

Figure 9 is an enlarged. detail, perspective View taken on the line 9-9 of Figure 8;

Figure 10 is a detail. perspective view showing the connection of one of the bulkheads with the pontoon bottom;

Figure 11 is an enlarged, perspective view showing a portion of a bottom chord in the plane of the section line l I-II of Figure 8;

Figure 12 is an enlarged. sectional View taken on the line lZ-IZ of Figure 2;

Figure 13 is an enlarged sectional View taken on the line l3-I3-of Figure 12; and

Figure 14 is an enlarged perspective viewtaken on the section line I fl-l 4 of Figure 12.

A pontoon hull 2U (Figure 2) has bulkheads 2| 'connecting reinforcing vrelements 34 and to 24 running from side to side, fore and aft of the middle of the pontoon; and

bulkheads

25 and 26 extending from end to end. All bulkheads are rigidly united at the intersections. There is a buoyancy chamber in the pontoon between the

bulkheads

22 and 23, but all of the other compartments formed within the hull by the bulkheads are preferably flooding compartments for sinking the dry dock. The location of the starboard wing wall section carried by the pontoon is indicated at 28, and of the port wing wall section by the broken lines 29. Framing trusses 30 extend parallel to the

bulkheads

25 and 26 on both sides of each, with extensions at intervals beyond the bulkheads 2i and 24 running out to the ends of the pontoon as seen in Figures 1 and 8. These trusses occupy most of the interior of hull, but are supplemented by a pair of trusses 36a and extensions Sia (Figures 1 and 2) one at each of the longer sides of the pontoon.

The trusses 39 rigidly connect the transverse bulkheads 2l and 22 in the port half of the pontoon and the bulkheads 23 and 2d in the starboard half of the pontoon. Beyond the bulkheads 2! and 24 the extensions are indicated at 3l; these are not so close together as the trusses 3i). In the illustrated embodiment, every other one of the trusses 36, with reference to either of the

bulkheads

25 and 26, has an extension 3l. Each of these trusses and extensions, and each side truss 30a and its extension 3Ia form a single continuous reinforcing truss member. The trusses 3!) may be continued across the buoyancy chamber at a suitable number of points, if desired; see the broken lines between the

bulkheads

22 and 23 in Figure 2.

The

bulkheads

25 and 26 are continuous and traverse the width of the buoyancy chamber between the

bulkheads

22 and 23. Between the latter bulkheads the hull is further reinforced and braced as set forth below to give it the strength required. When the pontoon is assembled side by side with otheri pontoons to make a dock, as set forth in my above-mentioned aplplication, with the bulkheads 2|, 22, 23 and 24 and the wing wall sections on each of the pontoons all in alignment with these bulkheads and wall sections of the other pontoons; and a ship is moved in for repairs; the weight of the ship is borne upon keel blocks, indicated at K, Figure 2 on the floor or deck of the dock, in the middle; and bilge blocks. indicated at B set up near the .lines of the bulkheads 2l and 24. Each row of blocks bears about one-third of the total weight of the vessel.

I shall first describe the outer trusses 33a and the extensions Sla within the pontoon at each long side of the hull, parallel to the

bulkheads

25 and 26, as shownin Figure 1. This sectional view illustrates deck plating 32 and a top beam 33, also parallel to the

bulkheads

25 and 26; and reinforcing elements 34 arranged crosswise thereof, The pontoon has bottom plating 36 with similar elements 31 and bottom chords or beams 38, extending in the same direction as beams 33. The

beams

33 and 38 and the members 3!! and 31 lie between the

bulkheads

2i and 22, 23 and 24. Between the extremities of the pontoon and the bulkheads 2l and 24these beams are extended in somewhat modified cross-sectional form as shown at 33 and 38' (Figure l) and the Y 3? are in the same part of the pontoon. At the 'very ends, fore and aft, each of the beams 38' widens outl into a broad web and runs up to the deck, as shown in Figure 1 at 38a.

Along these sides, further, between bulkheads 2| and 22, 23 and 24, and beyond the bulkheads 2| and'24, uprights 33 unite the upper beams 33 and their extensions 33'; at their junctions with the upper members 34 and 3-t; to the lower beams 33 and t8 at their points of intersection with the lower members 3l and 3l'. Alternate uprights 33, which are I-shaped in cross-section, of trusses a and all uprights in extensions Stu are connected with the

top beam

33 and 33 and

lower beams

38 and 38 nby diagonal braces 59. These braces 4Q are made fast to the uprights 39, at points midway between the upper and lower ends thereof, by `gusset plates 4|, to form frames that are K-shaped. All of the uprights 39 are connected at the same points with horizontal braces or channel .beams 42, which join the K-frames of each truss at their centers. vBeams 42 are also affixed to the bulkhead at the buoyancy chamber and to a plate 33h at the edge of the web 38a.

There are horizontal stiifening members or ribs 44 secured to the bulkheads 2|, 22, 2?, andZll. A rectangular coaming 4t is secured on the deck of the pontoon at each end and serves as the support for the section of the wing wall which is there mounted on the pontoon. Each coaming extends across the pontoons full width and its two long sides lie in approximately the plane of the outermost uprights Y33, and the plane of the nearest bulkhead 2| or 24.

On one face of each of the

bulkheads

22 and 23 at each side of the middle of the pontoon are vertical .stilening ribs 23a, T-sha-ped in crosssection, presented to the bulkheads 2| and 24 and anchoring the adjacent ends of the channel `beams Y42. These ribs are welded-to the deck and

bottom beams

33 and 38. At their junction with the latter are gussets lila to which the lower ends of the adjacent diagonal ,braces til are welded. Between each of the

bulkheads

22 and 23 and the outer ones 2| yand 24, the uprights '3S and braces 4B are illustrated as providing four K- frames, starting at the former and ending at the latter; and two more such frames beyond bulgheads 2! and 24. All diagonm braces welded to the faces of Athe plates 5i `which are m tum welded along one edge to the edges oi the anges or" uprights 3s; and the outer faces of the bulkheads 2i and are also reinforced in the planes of the trusses 3io by `Vertical ribs 3.9 comprising angle beams welded along `their outer edges, as shown in Figure l.

Figure 4 shows the connection between the diagonal braces t@ and the bea-ms 3,3 and .3S and their extensions. Each vdiagonal brace do is angle member and attached to the top of *ne beam shown for example at with one its flanges Vertical and in the vertical plane of the web of the beam. The brace is bevelleo. with the top of the beam, and the other or flange of the. brace rests on thetopoi the b o.

An extension it is welded to the web and flange of the beam and to the end of the ange of the brace in such a position that it forms, in eiiect, a continuation of the other or side flange of the diagonal brace 4i).

A splice plate 45 has its upper portion welded edgewise to the outside cr back ei the vertical flange of each diagonal brace 40, and its lower portion welded to the remaining face of the vertical web of the beam 33. The `cut-out or recessed portions El l(Figure 3) of the parts ci and 48 are for fitting the edges of the flange 6 of the beam V38. The top braces are similarly secured at -their upper ends,

Between each of the

outer bulkheads

24 and 2|, and the ends of the pontoon, the two additional `K-frames along the `sides have their centers in similar uprights; and are attached to the beams 33 and 38' in the saine way; :except that the diagonal braces of the first are made fast at their ends near the deck bottom beam extensions to the upright `reiirforceinents 33' upon said bulkheads.- The channel beams @2 extend from said bulkheads through these two K-frames also and are joined, as already stated, to the widened portions 38a of the beams at the ends of the pontoon. These beams are pieced at the bulkheads 2| and 2Q, and secin'eiy welded thereto.

Thus a complete truss or girder made up of K-frames extends from each bulkhead i2 and 23 out past the bulkheads 2| or 24 to the two ends of the pontoon along either side.

Figure 5 shows the design and arrangement of these trusses Sla along the sides, beyond the longitudinal bulkhead 24; the plan beyond the bulkhead 2| being the same. This View also f depicts the

longer bulkheads

25 and 26 and with stiffening ribs lil extending horizontally along same andthe intersecting bulkheads. Manholes such as appear at 5| .are provided near the lower end of the bulkheads 2| and 24 for access from one compartment to another. When the dry dock pontoon is in use, each manhole 5| is preferably closed by a plate, and each of the compartments is provided with its own piping for flooding or pumping water from the compartment. Similar manholes are provided in the other bulkheads wherever needed.

The construction of the trusses Sil and the extensions 3! is best illustrated in Figures 5, 6 and 8. The trusses 3l! include horizontal upper chord members made of beams 52 and lower chord members embracing beams 53, connected together by upright beams .or columns 54 and diagonal braces 5E. Each deck chord consists of two parallel beams 52, each bottom chord of similar beams Y53, extending from the

bulkheads

22 and 23 out to the bulkheads 2| and 24. They lie between and outside of the '

bulkheads

25 and 26. The vdiagonal braces 55 comprise opposed angle bars connected together by batteri plates 5l, The trusses all have uprights 54 that are I-shaped in cross section. A section through the trusses 30 is shown in Figure 6 to indicate how the uprights V54 are inserted at their ends between the

beams

52 and 53 and united thereto; the braces 53 having their ends attached to these chords in the same manner.

The braces 56 are omitted from Figure 6 for the sake of clearness. But Figure '7 illustrates the manner in which the diagonal braces 56 of the trusses 3b are connected with the uprights 54 at approximately the mid-points of the latter, by means of gusset plates 53 welded to the flanges of the braces and uprights. The trusses 30 are cross-connected with one another by channel beams 43, welded to the outside surfaces of the anges of the uprights 54, with reinforcing plates 59 welded to the inside faces of the flanges and to the websof the uprights 51E in such a position as to form, in effect, a continuation of the sides of the channel beams 43. This construction gives the cross beams 43 the same strength as if they were continuous, and at the saine time does not weaken the uprights 54 by cutting through their nanges. The beams 43 join the centers of the K-framesfrom the channel beam 42 on one side of the pontoon to the channel 42 on the other and are rigid with the

bulkheads

25 and 26 where they connect with same. These beams reduce the free, e'lective span of all the uprights in the trusses by half, and reduces the amount of material otherwise needed. The construction of the truss extensions 3| is similar to that of the trusses 36.

Figures 1 and 6 show the K-trusses 36 arranged relatively close together between bulkheads 2| and 22, 23 and 24; and Figure 5 shows how the truss extensions 3| are farther apart in the spaces between the bulkheads 2| and 24 and the ends of the pontoon. On either side of each of the

bulkheads

25 and 26, the extensions 3| coincide with and are continuations of every second truss 36. In Figure 5 the positions of the trusses 30 not extended are indicated by the plates 58.

.Figure 9 shows the bottom chord or beam structure of truss 36, between the bulkheads 2| and 22, 23 and 24. Parallel structural members, preferably T-sections 6|, with the bottom plates 36 of the pontoon welded to them, have the webs extending upward, and angle bars 62 are welded to the upper edges of the webs of the T-sections 6|, the remaining flanges of the angle bars extending outward. The angle bars 62 are connected by batten plates 63 at spaced points along their length to give a chord that is compound in structure. There are limber holes 64 along the lengths of the T-sections 6| for the passage of water. The top chord with beams 52 is similar. The deck and

bottom beams

52 and 53 are crossbraced at the requisite number of points by

ribs

34 and 31 respectively, rigidly attached to said beams.

Figure 10 shows the union of the bulkheads and the pontoon deck and bottom plating. 'I'he bottom edge, for example, of the plating of the bulkhead 25 is shown welded to the upstanding web of a T beam 66. The bottom plating is welded to the ilange of this beam. All the bulkheads i.

may similarly be connected with the top and bottom plating of the pontoon hull.

Figure l1 shows the construction of the bottom chord of each truss extension 3| near the ends of the hull, at the places where it is intersected by bottom stiffening ribs 31a. These ribs are preferably constructed with recesses along their lower edges, to which are welded the bottom plates 35. The recessed or serrated edges also allow passage of water. of Figure l1 involving the parallel beams 53 differs from Figure 9 in that at bars 6| take the place of the T-sections 6|, for in the truss extensions 3| less strength is required. The beams 53' of these extensions are thus cross-braced by ribs 37a fastened thereto at various points.

Each upper chord of the truss extensions 3| comprises similar parallel beams 52 between the bulkheads 2| and 24 and the ends of the pontoon of slightly less height than the beams 52. These beams 52 are also cross-connected along their edges, andcross ribs 34 of any suitable size and shape are attached between these beams.

In the trusses 3G, the bottom ends of thelower braces 56 are anchored further between gusset plates 56a and 56o adjacent the lower beams 53, and welded to these plates. Reinforcing ribs 23' on the faces of the bulkhead 23 (and 22) connect the deck beams 52 to the bottom beams 53, and the plates 56a unite these ribs to the beams 53. The plates 55h are attached to the beams 53 and lower ends of uprights 55, and the lower ends of adjacent braces 56 and uprights 54 are between them and beams 53 and attached to same. The braces 56 of the extensions 3| (ex- The bottom chord construction cept adjacent the bulkheads 2| and 24) are also reinforced by similar plates 56h at their junctions with upper and lower beams 52 and 53'. The braces 56 of the extensions 3| nearest to the bulkheads named are secured above and below with their ends partly between the beams 52' and 53', and reinforcing ribs 54a, attached to the adjacent faces of these bulkheads and uniting the deck beams 52 and bottom beams 53'. The uprights 54 and braces 56 as stated above, are enveloped at their ends by the

beams

52 and 53 and welded to the inner face of the bars 6| and 62. The uprights 54 of the trusses 3| are welded at their ends to the beams 52' and 53 at the flanges thereof; and the angle-bar braces 56 are welded to the inside faces of these beams, the same as the braces 55.

The terminal K frames of trusses 3| at bow and stern, comprising diagonal braces 56' joined at deck and bottom to

beams

52 and 53 are secured at their adjacent ends to gussets 58' on partitions or auxiliary bulkheads 59 extending across the extremities of the pontoon. The

beams

52 and 53 terminate at these partitions and the remaining space is braced.and divided as may be necessary.

Figure 13 illustrates the manner in which the six bulkheads are connected with one another. Each of the bulkheads 25 (and 26) is of composite construction and comprises plates or webs 68 between bulkheads 2| and 22, 23 and 24, connected at one end with a solid column 69.

Each of the

bulkheads

25 and 26 also includes plates 68 beyond bulkheads 2| and 24, connected to the other sides of the solid columns 69. Such a column 69 is located at each junction of the

bulkheads

25 and 25 with the bulkheads 2| and 24. The bulkheads 2| and 24 are made up of plates or webs welded to opposite sides of the column 69.

Each column 69 is considerably thicker than the plates 66 but is preferably provided with vertical stiiening ribs 'lil comprising T-sections welded to one side. The portions of the

bulkheads

25 and 26 that extend through the buoyancy chamber are made of plates 'll much thicker than the plates 68 in order to provide greater strength between the

bulkheads

22 and 23, which are subject to considerable pressure when the pontoon is flooded. For clearness the parts 69 and 'I9 are omitted in Figure 8.

Figure 14 shows the construction by which the

bulkheads

25 and 26 are reinforced. In addition to the horizontal ribs 44 with serrated edges welded to the face of the bulkheads, there are upright flat bars or plates 'I3 welded to the bulkheads and the outer edge of each bar or plate 13 is stiiened by a T-bar 14 welded to the edge of plate 13. The stiiening ribs 44 extend through openings in the plates 13. For the sake of clearness, these ribs 44 have not been shown in Figure 8.

The horizontal channel beams 43 uniting the K-frames of trusses 3D and 36a and extensions 3| and 3|a are also attached to the

bulkheads

25 and 26 in sections; one length having its end welded to the flange of the T-bar 14 and another length being connected with the other side of the bulkhead 25 by a gusset plate l5. There are plates or bars 'I1 between the anges of the T- bars and bulkheads that form in effect continuation of the channel beams 43.

The construction at the sides of the pontoon between the outermost trusses 30a and 3|a is indicated in Figures 5 and 6 but need not be L! detailed herein. These parts are reinforced and divided between the sides and the uprights 33; so as to support the outside plating and close the pontoon, but the load stresses fall upon the trusses only.

All of the connections described herein are welded, but the invention is not limited to welded joints and seams and some members can be used with rivets or other fastenings. Various changes and modications can be made and some ofthe features oi the invention can be used without others.

In the trusses 32a and 3m the uprights Stall have the same dimensions; and so do the upper braces ll. The lower braces il are a bit lighter except the one nearest the end, which is of the same size as the top braces. rhe lower braces are stressed more evenly by the buoyancy load; but at the outer end of the extension 31a the upward bending moment is greatest. Hence the lower brace lli) at this point should be somewhat stronger.

As for the trusses 3.5, and 3i the uprights 5,4 and 5d are all a bit lighter than the upright/s 39, but those of the extensions 3l are heavier and stronger than in the trusses 3Q. The -iraines oi these trusses 3! and the extensions Si are also lighter than in the trusses 35a and Sia, but are so designed that the braces 5t at the ends of the pontoon can well resist the upward bending i moment due to buoyancy; and the braces in the extensions Sia at the bulkheads 2l and 26 are suited to the weight loads of ship and wing wall section above and buoyancy below. The upper braces in the trusses between the

bulkheads

2i and 22, 23 and 2G are lighter than in the trusses 3Go; and the remaining braces, upper and lower, in both trusses and extensions 3l, espe cially the upper and lower braces in the three remaining K-frames of the latter between the K-frames at the ends thereof and bulkheads 2l and 24 are lighter still than in extensions Bla because the stresses are less and those due to the buoyancy loads are evenly distributed.

The central buoyancy chamber between the

bulkheads

22 and 23, has a relatively light central bulkhead It and is traversed by the two

long bulkheads

25 and 26. This chamber also contains room for machinery, crews quarters, storage and fuel space, etc. Between the

bulkheads

22 and 23 are reinforcing members 52A which are in line with the chords containing the members 52 and 52'; thus forming composite beams that are continuous from end to end of the hull. The waist of the hull containing this chamber is iurther reinforced by iiooring and other members as required.

The unit stresses due to buoyancy load are reduced because the pontoon is lengthened beyond the wing wall locations. At the same time a more ecient beam effect is produced by the tapering ends of the hull.

It will be noted that the trusses S-Sa are all relatively close together. Hence only two

bulkheads

25 and 25 running from end to end are needed; and in a pontoon 250 feet long by 80 feet beam, for example, these bulkheads will be over 30 feet apart. The trusses stiften the other bulkheads and enable them to withstand the weight of ship and wing wall sections. Both weight loads and buoyancy loads are transmitted by the trusses to the

bulkheads

2l, 22, 23 and 24; and through these to the

bulkheads

25 and 26. In the usual design of dry dock pontoon, with a single central bulkhead parallel to the side walls,

transverse, bulkheads running in the sal-nedirec',v

tion as

bulkheads

25 and 26 are added in such number that in a structure of the dimensions specified above, they will be only 8 feet apart. The replacement of most of these by K-trusses aflfords a great saving in steel, without loss of strength. The trusses make the bulkheads 2l to 2t rigid; these in turn, especially Vin combination with the cross beams d3 uniting the K-irames of the different trusses, stiften the

bulkheads

25 and 25 so as toobviate all risk of buckling, warping ory other distortion. These cross beams also brace the side plating. to the extent demanded against the outside pressure of the water; the

bulkheads

25 and 25 and channel beams 52, and trusses 3l and Sig, also having the like result with respect to the outer plating at the ends. The general eiieet is to make the bulkhead, framework and deck and'bottom plating so rigid that the bulkheadsvirtually become girders; with the deck and bottom plating serving as the flanges, and the bulkheads themselves as the Webs; and the cross,- beams d3 have the additional utility of so bracing the K-frames at the centers that the spans o f the uprights 3.9, 5d and 54 is only half their length. IThis too, increases thev strength and con tributes to the general saving in materials oi construction.

As indicated in Figures 8 and 12, only the ex,- tension Si in the very middle of the pontoon will have five i -frames Those at each side will have ewer because the hull is ship-shaped, as set forth in my co-pending application for patent above mentioned. rThe transverse end bulkheads 59 are of less height at the ends where they are attached to the bulkheads 25 and 25 (Figure 12). The lower edges of these bulkheads curve upward near the extremities as Figures 8 and l2 illustrate. But the four cross-beams 43 of the extensions 3l extend all the way across the ends from one side to the other.

The deck and bottom plating reinforcing ribs, beams, uprights, braces, bulkheads and all other members, are securely welded in their various parts and in their respective positions to make the pontoon as strong as possible at all points. rhe construction described is well adapted to attain all the objects of the invention.

Having described my invention, what I believe to be new and desire to secure and protect by Letters Patent of the United States is:

1. In a hull for a dry dock the combination of trusses, each of which has a deck beam, a bottom beam, uprights connecting said beams, braces f uniting said beams to points between the ends of the uprights, and beams uni-ting said trusses to one another at said points.

2. A hull for a dry dock pontoon containing trusses, each of which includes a deck beam, a bottom beam, uprights between the beams, diagonal braces connecting the uprights at points intermediate their upper and lower ends to said beams, a beam uniting said uprights of each truss at said points, and cross-beams connecting the .trusses together at said points.

3. A hull for a dry dock pontoon containing longitudinal bulkheads, transverse bulkheads intersecting said longitudinal bulkheads adjacent the ends of said pontoon, vertical columns at the intersections, said columns being of greater thickness than .the bulkheads and said bulkheads being made up of sections that have their ends permanently connected with said columns throughout the length of the latter, and a transverse bulkhead at each side of the middle of the 11 pontoon intersecting the longitudinal bulkheads, the latter being of greater thickness between the last-named transverse bulkheads.

4. A hull for a dry dock pontoon having intersecting, rigidly connected bulkheads and .trusses comprising K-frames crossing some of said bulkheads and fixed thereto, said trusses being substantially parallel to the remaining bulkheads, and connected transversely to one another adjacent the midpoints of said frames.

5. A hull for a dry dock pontoon, comprising a pair of bulkheads between each end and the middle of the hull, additional bulkheads extending from end to end intersecting and united with the aforesaid bulkheads, and trusses 4parallel with said additional bulkheads, said trusses uniting the members of each pair of Ithe aforesaid bulkheads, and some of said trusses being extended beyond them towards each adjacent end of the hull.

6. The hull according .to claim 5, having cross beams at predetermined points connecting said trusses and said additional bulkheads.

7. A hull for a dry dock pontoon having a pair of bulkheads between the middle and each end, additional bulkheads extending from end lto end and intersecting and united with both pairs of bulkheads, trusses comprising K-frames between and along the outer sides of the additional bulkheads, said trusses connecting the aforesaid bulkheads of each pair together, some of said Itrusses extending out lto the adjacent ends, `and a beam connecting the K-frames of 'some of the trusses together at the centers of the latter.

8. The hull according .to claiml 7, having cross 12 beams to connect the centers of the K-frames of the trusses to .the additional bulkheads.

9. In a hull for a dry dock pontoon, the combination of parallel top and bottom beams arranged in pairs, bottom plates attached to the lower edges of said bottom beams, ythe upper edges of said plates having out-turned iianges, stiffening ribs passing through said beams, transverse battens secured to said flanges, uprights secured to the top and bottom beams, and braces secured to the uprights and the opposed faces of said pairs of beams.

10. A hull for a dry dock pontoon, having inside .trusses extending side by side, from the middle towards the ends of said hull, bulkheads spaced from the ends of the pontoon and intersected by said trusses, some of said trusses being shorter and some longer than the remainder, the longer projecting beyond said bulkheads, the shorter .trusses terminating at said bulkheads and short of said ends.

11. A hull for a dry dock pontoon, having trusses within the hull, said trusses extending side by side from the middle towards the ends, bulkheads spaced from the ends of the pontoon and intersected by said trusses, some of said trusses being shorter and some longer than the remainder, the longer projecting past said bulkheads, the shorter ones terminating at said bulkheads and short of said ends, and the longer trusses having relatively heavy portions at said ends to resist upward bending moments.

FREDERIC R. HARRIS.