Bolted Sectional Dock Lifting a Vessel.
The Callao floating dock, the towing of which to its destination from the Tyne was the most hazardous towing feat ever accomplished, merits special attention, both on account of the completeness of its equipment and of the extraordinary interest which was manifested in its journey. It is one of the double-sided self-docking type, known as “bolted sectional,” and is divided into three separate portions. It is capable of lifting vessels having a displacement of 7000 tons, but it is so designed that this lifting capacity may be increased to 9500 tons at some future period by the addition of a fourth section, making the over-all length about 510 feet, the present length being 385 feet. Its extreme width, i.e., the clearance between the rubbing fenders, is 70 feet, and the draught over keel blocks is sufficient to take vessels drawing 22 feet. As in previous floating docks built on the Clark and Standfield principle, each section has its own independent pumping machinery and steam-supply. Such usual accessories as keel and bilge blocks, mechanical side shores, rubbing timbers, flying gangways, head capstans, &c., are supplied, and there is also a heavy mooring outfit of anchors and cables. The dock was launched in June 1908, and at that time satisfactorily completed a self-docking trial by lifting one of the end pontoons alongside the Wallsend shipyard. For this purpose the three sections of the dock were disconnected, and the two end sections were turned round end for end, so that their points came opposite to the central section which is square-ended. They were then lowered under the water and drawn in under the central section. On pumping out the end sections they rose, bringing up with them the central section, which was then resting on their pointed ends. The dock left the Tyne on August 20 of that year, in charge of the powerful Dutch tugs Roodezee and Zwartezee, each of which has an indicated horse-power of 1500, their bunker capacity being 650 tons and 600 tons respectively. The dock in its journey to Callao was manned by a captain, mate, engineer, and nine sailors.
It was fastened to the tugs by extra superior Manila ropes of 18 inches, with 30 fathoms of flexible steel wires of 4¹⁄₂ inches circumference on both ends, while each tug had on board a new spare rope of precisely the same size and quality. One tug broke down on the way, and another had to be sent to Monte Video to take her place.
The time taken on the journey was 225 days, but after deducting the delays in the Thames and at Monte Video, the time occupied on the passage was only a little over four months.
The long voyage down the Atlantic, culminating in the passage of the dreaded Straits of Magellan, caused the vessel to be kept upon the marine reinsurance list almost from start to finish.
The distance from the Tyne to Callao does not represent a world’s record for a tow of this nature, inasmuch as it has been exceeded by the Dewey Dock built by the Maryland Steel Company of Baltimore for the United States Government, which, in the summer of 1906, was towed from America to the Philippines, a distance of 13,089 miles, in 150 days.
Great Britain, though a large builder and the principal designer of floating docks, does not possess very many; possibly the number and excellence of the dry docks scattered round her coasts may be the explanation. But as dry docks are costly to make or alter, the British Admiralty has ordered the construction at Wallsend of a floating dock which will take the largest battleship afloat or likely to be built for some years to come. In anticipation of the possible needs of the mercantile marine, plans have been prepared for a floating dock with a lifting power of 45,000 tons.
The largest floating dock in existence at present is at Hamburg, which has a better equipment in this respect than any other port in the world. It was built by Messrs. Blohm and Voss, the shipbuilders, for their own use, and was completed last year and can lift 35,000 tons. Hamburg has altogether eighteen iron and steel floating docks. Bremen has three large floating docks, two of which, if used together, have a lifting power of 3300 tons. The third dock, 385 feet long by 83 feet inside measurement, can lift a vessel of 10,500 tons.
Other countries also have provided themselves with floating docks; indeed there are few nations of any importance which have not several floating docks, modern in type, of great lifting power, and thoroughly equipped. A few, like Austria, reserve the docks for naval purposes only.
