152 BUOYANCY AND STABILITY OF TROOP TRANSPORTS. 



lowering of the boats on both sides of the ship, that is, the hst should probably 

 not be greater than from 5 to 10 degrees. It must be borne in mind, however, that 

 when holes are provided in the longitudinal bulkheads, as recommended above, a 

 rapid equalization will take place immediately after the accident and the list may be 

 expected to decrease very fast during the first few minutes, unless other causes, 

 tending to increase it, intervene. It seems reasonable, therefore, in estimating the 

 residual metacentric height, to allow a somewhat greater angle of heel, depending 

 on the nature of the longitudinal subdivision. Assuming a permissible initial list of 

 from 10 to 15 degrees, it is found that the residual metacentric height should prob- 

 ably be not less than from lyi feet in transports of about 500 feet in length to 2^/4 

 feet in transports of the largest size. This gives a metacentric height in the light 

 intact condition of from 3 to 4 feet, but these figures must be regarded only as 

 average values, applicable to ships of existing type suitable for that service. 



In the full-load condition the freeboard and hence the range of stability is a 

 minimum, but, on the other hand, the metacentric height is likely to be greatest and 

 does not in general suffer so much reduction by bilging. Again, if the stability is 

 sufficient in the light condition, it will generally be sufficient when the ship is fully 

 loaded, but probably the metacentric height should not be less than from about 4^ 

 feet in smaller transports to 5^ feet in transports of the largest size in the intact 

 full-load condition. Here, as when in the light condition, each ship must be dealt 

 with independently and on its own merits. 



As might be expected, these requirements are not fulfilled in ordinary passenger 

 steamers as operated under peace conditions. The Empress of Ireland, which, as 

 described below, was lost in a collision, had a metacentric height of 3^^ feet when 

 the collision occurred, at which time she was practically in the full-load condition. 

 This was reduced to 2^ feet* by flooding of the boiler rooms. In a troop transport 

 of the same size the metacentric height should be about i foot greater. Had doors 

 and side lights been closed on the main deck and had holes been provided in the 

 side-bunker bulkheads, the list would soon have been reduced by equalization to 

 less than 10 degrees, in which case the ship would probably have remained afloat and 

 boats could have been lowered on both sides. 



The George Washington, which has no longitudinal subdivision, satisfies prac- 

 tically the above requirements, having a metacentric height of 2^ feet in the light 

 condition and 4j4 feet in the full-load condition, but in the Leviathan these figures 

 are 3 feet and 4 feet and in the Mount Vernon 2.1 feet and 3.2 feet respectively, 

 showing that these vessels, which have many longitudinal bulkheads, fell short of 

 the requirements. 



BALLASTING. 



In order to secure the metacentric heights specified above, most passenger 

 steamers used as troop transports must carry some ballast, at least when they are 

 in the light condition. Ocean-going passenger steamers are in general designed 



* According to the lost buoyancy method. 



