28 ANNUAL OF SCIENTIFIC DISCOVERY. 



few hundred tons had been exerted, onr huge derrick, vessel and all, would 

 begin to careen, and would ultimately pull itself over upon its beam-ends, 

 the sunken ship sticking in the mud as before. Here comes in the chief fea- 

 ture of the improvement. The entire hull, as we have seen, is a honey- 

 comb of water-tight compartments, those on the side opposite the derrick 

 being capable of holding 1700 tons of water. Two pair of steam pumps, 

 of two feet stroke above each, capable of throwing 60 tons a minute, fill up 

 these compartments from the sea, as fast as the strain on the pulleys increases, 

 so that the sunken vessel on one side, and the water-cells on the other, just 

 balance each, and the empty compartments under the derrick hold the whole 

 mass afloat. The entire draft of water in this case will be only nine feet. 

 The pumps also throw out the water as the strain decreases. One of their 

 most useful offices will be to free stranded ships. 



How to propel this great craft was not a simple question. There not being 

 draft enough for either screws or paddles, an old device was rejuvenated, 

 viz. : On each side two skeleton drums, resembling two paddle-wheels, were 

 placed, one near the bow, and the other near the stern. Over these pass 

 endless chains, on which are secured the floats or paddle-boards, some twen- 

 ty-four being immersed at a time. So the vessel crawls like a centipede at 

 the rate of seven knots an hour. The four propelling engines are of eighty 

 horse power each, and are entirely under the deck. It is evident that this 

 craft cannot be easily wrecked, for its width will prevent its capsizing; and, 

 although seas may sweep its deck, they cannot break through nor strain it, 

 for the entire hull is a girder of almost immeasurable strength. Should it 

 collide and fill half its compartments, the rest will keep it afloat. 



It having been impossible to secure a large vessel near London, on which 

 the giant could try its hand, its only experiment has been the lifting of a 

 couple of smaller ones. Six of the pulleys were secured by chains, forming 

 a cradle, under an old brig of 300 tons, weighing some 270 tons, and draw- 

 ing some ten feet of water. In fourteen minutes it was raised about twenty 

 feet in the air; the engines making ninety-four revolutions per minute. A 

 small iron steamboat, weighing sixty tons, was then run underneath, and at- 

 tached to the suspended brig. The engines being again started, both vessels 

 were raised high in the air, presenting a singular spectacle never before wit- 

 nessed. The derrick sank but thirteen inches under this increased body of 

 335 tons. This is, perhaps, the greatest weight ever raised at a dead pull. The 

 machinery is so arranged as to be quickly and easily handled by a few men, 

 and the entire demonstration on this occasion was satisfactory. 



The method of raising a sunken ship would be as follows : The derrick be- 

 ing on one side of the ship, an accompanying steamer takes out two chains, 

 and, dropping them so wide apart as to embrace both stem and stern of the 

 sunken ship, returns them to the derrick. A new instrument here comes into 

 use. It is a bar of iron five feet long, with large holes in both ends, and a 

 pear-shaped mass of iron, weighing a ton and a half, suspended from the 

 middle. Both chains having been passed through one of these " divers," at 

 one side of the sunken ship, and through another at the other side, both 

 divers are dropped to the bottom, and tend to draw together, and hold the 

 chains under the ship. By hoisting more on one chain than on the other, 

 one end of the ship may be raised a little, and the sticking of the mud thus 

 overcome by a great leverage. When one end is raised, the other chains are 

 similarly slipped under, without the aid of living divers, till they form a cra- 

 dle under the ship, which is then lifted bodily, the pressure of the water of 



