GREAT EASTERN. 



503 



bose for fear of accident, two at each end. 

 These were carried some distance above the 

 water, and one of them was supplied by the 

 ship's pumps discharging into it continuously, 

 the surplus passing out of the upper nd of 

 one of the others. As a further precaution 

 agaitist the admission of water at the gun- 

 wale, there was a flap of Brussels carpeting 

 four inches wide, the inner edge battened to 

 the outside of the gunwale, and the outer sewn 

 to a bolt rope to prevent it from being drawn 

 into the joint. As the hose answered its 

 purpose, there was not draft to hold the flap 

 to the side of the ship. The caisson was 

 built bottom up for convenience of planking, 

 launched that way, and towed to the der- 

 rick at the Novelty Works and turned over, 

 and then towed to the ship. To bring the 

 caisson into position two heavy timbers were 

 placed on the ship's deck, and projected over 

 the side at the extremities of the caisson in 

 position. Two heavy timbers were also placed 

 in like manner for hoisting the entrance 

 shafts. Blocks and tackle were attached to the 

 extremities of these timbers, and connected 

 with the caisson and shafts, and with the ship's 

 capstan ; chains, secured to eye bolts in the 

 port side of the caisson near its ends, were 

 carried down beneath the bottom of the ship, 

 and were drawn up and secured by tackles at 

 the starboard side of the ship ; 2 chains led up 

 to the davit tackle on the port side of the ship. 

 To overcome the buoyancy of the caisson 26 

 tons of iron ballast were necessary, and the 

 engineers determined to use chains for this 

 purpose, as when the caisson was in position 

 the chains could be drawn out through the 

 entrance shafts readily, and the caisson would 

 then be pressed against the ship by its re- 

 gained buoyancy. To guide the caisson as it 

 was lowered, and to have the means of de- 

 termining readily when it was in position, 

 a large log 4 feet longer than the caisson was 

 ballasted and hauled under the ship by chains 

 at each end until its port side, which would 

 be next the caisson, was 18 inches to the star- 

 board of the required position of the star- 

 board gunwale. The position of the log lat- 

 erally was determined by the length of the 

 chains as let down from the port side of the 

 ship ; the log was let down a little ahead of its 

 position, and then drawn endways according to 

 the directions of the diver. "Wire rope guides (a, 

 fig. 3) had already been attached to each end of 

 the log at a distance apart to admit of the length 

 of the caisson between them, the loose ends of 

 these ropes were brought up the port side of 

 the ship and passed through eye bolts in the 

 ends of the caisson to guide it as it was lower- 

 ed into its place ; the upper ends of the rope 

 were secured to tackles at the extremities of the 

 end davits, so that they could be slacked or 

 tautened at pleasure. The ballast having been 

 distributed in the caisson so that it floated at 

 about the angle at which it was to be placed, it 

 was filled with water by the ship's pumps, the 



port chains being kept taut ; when filled it sank 

 and was lowered by the port chains to the 

 proper angle to receive the upper sections of 

 the entrance shafts, which had already been 

 raised by the intermediate davits ; the shafts 

 were then lowered and connected with the 

 nozzles on the caisson by bolts passing through 

 their flanges. As soon as the entrance shafts 

 were attached the caisson was lowered by 

 slacking the tackles at the four davits until it 

 had sunk a certain measured distance deter- 

 mined by the length of the port chains ; as it 

 sank it glided down the wire rope guides left 

 purposely slack. Then the caisson was drawn 

 laterally against the ship by taking up the star- 

 board chains, and at the same time guided to 

 its place by tightening the guide ropes. When 

 in contact with the ship and nearly in position, 

 divers were sent to report its progress, to see 

 whether it covered the fracture, and whether 

 its gunwale would come upon the centre of an 

 outside strake. When drawn into its right posi- 

 tion 4 heavy hawsers were placed under it and 

 the ship, to cramp it against the ship ; these were 

 hauled tight by the ship's capstan ; the chain 

 ballast was then drawn out, another pull taken 

 at chains and hawsers, and then to make a still 

 greater strain wedges were driven between 

 them and the sides of the ship. The caisson 

 was held in its place longitudinally by 2 chains, 

 one secured to an eye bolt in the front end of 

 the caisson, and carried forward at the side of 

 the ship, ahead of the paddle box ; the other 

 chain was attached to the rear end of the cais- 

 son, and carried aft into one of the stern hawse 

 holes. As first arranged, the pump (Andrew's 

 centrifugal) was secured in its place, at the end 

 of the frame K, before the caisson left the ship 

 yard, and an intermediate shaft attached before 

 the caisson was lowered. The small hose was 

 connected at the same time with the gunwale 

 hose, and when the caisson was in position, a 

 line was attached to the loose end by the 

 diver, and it was drawn up. In order to per- 

 mit tlae divers to examine-the interior gunwale 

 of the caisson, a foot board was secured to 

 brackets around the caisson about 4 feet from 

 the gunwale ; and at the suggestion of Capt. 

 Paton, cords with knots corresponding to their 

 distances from the forward end ot the caisson, 

 were attached at every fathom to enable the 

 diver to ascertain his position by feeling. On 

 examination the divers reported that the cross 

 timbers of the caisson bore against the ship in 

 certain places where the plates were bulged 

 out, whilst at their ends the gunwale was not in 

 contact with the ship's side. This had been fore- 

 seen, and blocks of soft wood (6, 5, fig. 2) had 

 been placed on the top of the cross timbers, 

 which could be split out to bring the gunwale 

 in contact with the ship. The cutting out of the 

 blocks was a tedious job, and occupied consider- 

 able time, and was done by divers, one split- 

 ting out the blocks, whilst the other held a 

 submarine lamp, and secured the chips and 

 placed them in a bag, to prevent them from 



