US2291076A - Floating dry dock - Google Patents

Description

July 28, 1 942. F. R. HARRIS FLOATING DRYDOCK Filed May l] l rial WITNESSiES INVE OR Patented July 28, 1942 I Urrso srrss sereni OFFICE FLOATING DRY DOCK Frederic R. Harris, New York, N. Y.

Appiication May 11, 1940, Serial No. 334,646

4 Claims.

My invention relates to an improvement in floating dry docks, and it is especially adapted for use in dry dock pontoons that are constructed of timber.

The object of my invention is to provide a strong, compact and economic transverse pontoon truss adapted to support a heavy ship load, which is shored on the center line of the dock.

Hitherto dry dock pontoons are given a rectilinear and rectangular box shape, to which form the pontoon trusses conform.

Therefore, in a conventional dry dock pontoon, a centrally located ship load is supported by a water pressure of constant intensity everywhere under the fiat pontoon bottom, and the transverse trusses therein must obviously be designed to carry not only the direct tension in the bottom chords due to the central ship load, but also the tension due to the bending of the rectilinear chord segments between panel points.

Now, however, I have discovered that by means of providing a round bottom in the pontoon and truss chords conforming with the pontoon bottom, the bottom chord tension, instead of being augmented by the outside water pressure, will be substantially reduced by a counter effective arch compression in the sprung chord segments between adjacent panel points.

Besides a substantial stress reduction in the main truss member, other major advantages that ow from my invention are as follows:

The cross section of my preferred dry dock pontoon is massed towards the center thereof, and the direct stresses due to the ship load are materially reduced.

The free water surfaces inside my preferred pontoon structure will gradually contract as pumping proceeds, and a considerable reduction of dock width, i. e., truss span, is possible as relatively narrow wing walls will suffice to stabilize the dock and the ship shored thereon during the docking operation.

In the drawing: Fig. 1 is a cross section of the dry dock and shows my preferred construction of a transverse pontoon timber truss. Fig. 2 is a fractional longitudinal cross section of the dry dock itself and shows a series of transverse trusses supporting the outside planking thereof.

Referring to the drawing, in which like reference characters designate corresponding parts, I denotes a iloating dry dock comprising a pontoon structure 2 which at its ends supports upright side walls or wings 3.

In the pontoon body 2 a transverse truss 4 is shown'provided with a preferably laminated bottom arch chord 5, in the upper side of which diagonally placed struts 6 are notched.

I prefer to fan out said struts from a point at the center of the truss directly under the ship load 1, and in my preferred truss construction a second laminated and arched truss member 8 is sprung over the top of the struts 6 and the bend down ends of the arched member 8 are connected to the outer end portions of the bottom chords by means of suitable chocks 9 and wedges ID, all held together as a rigid corner by suitable through bolts II.

I prefer also in my pontoon construction to lay the deck planking I2 directly on top of the top truss chord members I3, but I prefer to support the bottom planking I4 on floor beams I5 laid across the bottom chords 5.

Suliicient truss uprights I6 are also provided in the pontoon truss and tted between the top and bottom chords and the laminated members, their function being to transmit the external water pressures from deck to bottom when the dock is submerged, and also render the pontoon truss rigid when the dock is up.

Sufficient ballast, not shown in the drawing, is placed inside the dock structure so as to sink the dock when ilooded.

It is evident that when the dry dock pontoon supports a maximum ship, the pontoon deck will be approximately awash, and it is also evident that the pontoon truss should be designed to carry the maximum ship load.

When a ship is being docked and is just clearing the water, the entire dock stability is due to the side walls, which must balance the elevated ship moment as well as the upsetting moments due to the inside free water surfaces in the pontoon.

Obviously, in my preferred construction the free water moments grow less the more the pontoon is pumped out, while said moments remain constant in the conventional rectangular pontoon.

The inner free water is thus reduced to a minimum for a maximum ship load, and the width of the dry dock can therefore be materially reduced.

I do not wish to limit my claims to the construction shown as it is evident that alterations and modications may be made in the adaptation of my device for different purposes without departing from the spirit and scope of my invention.

I claim:

l. A oating dry dock pontoon comprising a round bottom, a deck, and a transverse truss between the bottom and deck, said truss including an arched bottom chord member curved to the shape of the round bottom and to which the bottom is connected, and diagonal braces extending from a central line of the pontoon deck to spaced panel points along the concave side of the arched bottom chord member, said panel points being so spaced from one another along the arched member that the water pressure exerted against the pontoon bottom and transmitted from said bottom to the portions of the arched bottom chord member between panel points compresses the arched portions with a Y' force that substantially relieves the tensioning of said bottom chord member by the load of a ship centrally located on the deck above the diagonal braces.

`down ends of said arched truss member to the end portions of the bottom chord member.

- 4. In a oating dry dock pontoon, having a round bottom section, a timber truss for sus- 2. A oating dry dock pontoon comprising a round bottom, a deck, and a timber truss between the bottom and the deck for sustaining a central ship load, said truss including a laminated and arched bottom chord member conforming with the outline of the pontoon bottom and to which the Water pressure against the bottom is transmitted, struts fanning out from a point close to and below the point of load application and notched in the top side of the arched bottom chord member at spaced points along said member, and means that transmit bottom pressure to the arched segments of the chord member between said spaced points so as to cause a substantial arch compression in the bottom chord member that substantially relieves the tension stress therein.

i taining a central ship load, comprising a laminated and arched bottom chord member conforming to the shape of the pontoon bottom, struts fanning out from a point close to and below the upper central region of the truss and extending to spaced panel points along the concave side of the arched bottom chord member, means for transmitting the bottom pressure to the arched chord member so as to cause a substantial arch compression of the segments of said chord member between said spaced panel points, a top truss chord member, and uprights tted between the top chord member and said laminated and arched bottom chord member.

FREDERIC R. HARRIS.

Images