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18 MARINE REVIEW. LARGEST DRY DOCK AFLOAT TO DATE. 'IT HAS JUST BEEN COMPLETED BY THE SPANISH GOVERNMENT AND IS NOW BEING TOWED TO ITS DESTINATION. The largest dry dock afloat has just been completed for the Spanish government by Robert Stephenson & Co., Ltd., at their Hebburn ship building yard, England. It is on the self docking pontoon order. The dock was originally intended for the port of Olongapo, the naval arsenal in the Philippine islands, but owing to the change of governmental ownership of the Philippines, it has now been decided to place the dock : EXTERIOR VIEW OF SELF-DOCKING PONTOON DRY DOCK. in the port of Mahon in the island of Minorca. The dock is of very strong construction, the Spanish admiralty making the following require- ment: If a ship of 12,000 tons weight, with a length of 328 ft., be placed in the center of the. dock, no part of the dock shall be worked to more than 6.33 tons per square inch in extension and 7.6 tons per square inch in compression. The bottom portion of the dock is built of iron and is composed of six pontoons, each 74 ft. 2 in. long by 117 ft. wide by 18 ft. 6.in. molded depth. On the top of those are placed the side towers, or girders, securely bolted to the pontoons and binding them all together. The pontoons are also connected together by junction plates extending across the dock at each pontoon end. The side girders are built of steel on account of their having to take the strain when a ship is docked, and also, as being mostly out of water they are not so liable to corrode. The pontoons are very strongly constructed, having eleven fore-and-aft bulk- heads, nine of which are water-tight, dividing each pontoon into ten water-tight compartments. This makes sixty water-tight compartments at the bottom of the dock, all of which were tested with a water pressure of 13 lbs. per square inch. Every fifth frame in the pontoons is a strong partial bulkhead ex- tending across the dock, and over these frames the bilge blocks are placed. The center girder over which the keel blocks are placed is 1 in. thick, and also under the keel blocks 4 ft. from the center on each side, two more fore-and-aft bulkheads are placed. Those with diaphragm plates on every frame make a solid foundation under the keel blocks. The side towers have a safety deck about 14 ft. above the pontoons which prevents the dock sinking altogether, supposing the inlet valves were by any chance left open. Each tower is also divided into ten water-tight compaitments. The center compartment of each tower is fitted up with the pumping installation, which consists of two large marine-type boilers working at 120 lbs. pressure and two of Tangyes' 24-in. centrifugal pumps, each worked by a separate engine, also one duplex drainage pump and fire pump, two duplex feed donkey pumps, and a feed heater. This in- stallation is duplicated in the other tower. Together, the four main centrifugal pumps are capable of throwing 23,000 tons of water against a 28-ft. head in two hours. The 26-in. main suction pipes and the main drainage pipes run along inside the side towers, and branch down at each pontoon to a collecting-box from which pipes lead to each compart- ment of the pontoons. Each of these pipes has a separate valve, worked by a rod and wheel from the top of the side towers. Each compartment has also a wrought-iron air pipe, which is led up the side towers and placed near the standard and wheel which operates the valve to the cor- responding compartment. At the top of the air pipe is placed a gun- metal cock. The inlet pipes, which are 19 in. in diameter, are also con- nected to the collecting or distributing boxes and each inlet pipe has a grid and valve worked from the top of the towers. Every water valve in the dock has an indicating plate and pointer showing how much the valve is open. Each pump, by means of valves, is arranged to draw from one or both ends of the dock, and each pump has a 24-in. valve on the discharge branch, and also a balanced flap valve. The drainage pump is also arranged to draw from each compartment through a sepa- rate range of pipes, and there is a gun-metal drainage foot valve at the bottom of each branch pipe to each compartment of each pontoon. The drainage pump is also connected to a range of pipes which are carried along the top of the side towers for washing decks or for fire purposes ' The compartments in the side towers are filled and drained through the main suction pipes, and they can also be drained into the pontoons b means of scupper valves worked from the decks of the pontoons | There are speaking tubes from each tower to the engine room and [July 25, ------. from side to side. The keel blocks, which are placed 3 ft. centers, are of pitch pine and are 3 ft. 6 in. high. The lower blocks are 18 in, 'square, and each keel block has a cap piece of oak 6 in. thick. The blocks are fitted between angle iron, and are securely dogged together. There are twenty-four bilge blocks of very strong construction placed on the dock, so that they can be shifted in or out, and on the top of each steel bilge block is a sliding block of oak, which is pulled into position under water by means of ropes led to the top of the towers. There are two shoring shelves inside the dock on each side, 2 ft. 6 in. wide, with a facing piece of elm 9 in by 6 in. The sides and ends of the dock are protected by two American elm fenders securely bolted between angles. _On the tower tops are placed fourteen large timberheads for mooring ships using the dock, and four mooring shackles are attached to the pontoon for mooring purposes. Wrought iron ladders lead up from the pontoons to the shoring shelves and tops of towers. On the inner side of the towers in the stokehold, water-tight doors are placed, giving access to the. deck of pontoon, and for discharging ashes. The engine room and stokeholds are ventilated by cowl ventilators and a range of ventilating pipes. Feed tanks are placed on each side above boilers, each holding 25 tons of fresh water for feed purposes. There are also bunkers which will hold 30 tons of coal in all. The dock has been so constructed that in the event of damage to a pontoon, or, if a pontoon requires a bottom to be scraped and painted, it can be detached and docked on the dock itself and repaired or painted. This is done by disconnecting the bolts that hold the pontoon to the side girders, and to the pontoons adjoining disconnecting the suction pipes and valve rods, and letting the water through the sea valve into the pontoon when it is disconnected. This causes it to sink below the level of the bottom of side girders, and it can then be easily drawn out at either side. It is then turned round so that the narrow part faces the entrance of the dock, which is next sunk sufficiently to let the pontoon float over it, the water is then pumped out and the pontoon raised. After painting, the process is reversed, and the pontoon brought back into place and rebolted to the side girders, The dock is being towed from Hebburn to its destination by three powerful tugs belonging to Messrs. Smit & Co., of Rotterdam, who make pareonaonnoes INTERIOR VIEW OF SELF-DOCKING PONTOON DRY DOCK. a specialty of long-distance towing of this description. The voyage is calculated to occupy thirty days. There are two tugs towing, namely, the Zwarte Zee, whose tow rope is of 20-in. manilla, and the Oceaan, having an 18-in. manilla tow rope. The steering is done by the Zuider Zee, whose check rope is of 13-in. manilla. The principal dimensions of the dock are as follows: Ft. da Length between perpendiculars....,......... 2... 2: 450 0 Breadth, moulded, over pontoons. ......0.. - 4a. dF 0 Depth: moulded,.of pentoons;..:.¢.. 6 i 2 i 13° 8 Camber of pontoon deck between side Binders. sc <5 9 Breadth, moulded, of side pirders, «..,..0. 0. 12 2 Depth, moulded, of side girders above pontoons...... 38 6 Distance Over side girders, moulded... (0 115 4 Distance between side girders, moulded.............. 91 0) Distance between shoring platforms 85 0 Distance between pontoons, moulded. < it 0 Will itt a ship -weletnne. | Coe 13,000 tons. Arnold S. Gruber of Nyack, N. Y., has organized the Rapid Boat Co. and will try to secure capital for the construction of fast passenger boats to compete on the Hudson river with railways operating between New York, Tarrytown and other towns up the river. This is the company that proposes to apply to passenger service on the Hudson the designs of C. D. Mosher of New York, who has built two or three "racers" that are said to have attained more than 30 knots speed. It is proposed to make the passenger boats that are now talked of about 130 ft. long and to fit them with quadruple expansion engines of 4,000 H.P. The scheme has not, of course, as yet developed much beyond the newspaper stage. ---------- Both the Carnegie and Bethlehem Stee] companies have made known to the navy department their willingness to enlarge their plants so that the government will receive 500 tons of armor a month from each-con- -- cern, or an aggregate of 1,000 tons a month instead of 600 tons.