140 BUOYANCY AND STABILITY OF TROOP TRANSPORTS. 



or design, the results are marked up as ordinates from the base line of a profile 

 drawing, which shows the location of the bulkheads, and a "floodable-length curve" 

 is drawn through the points so obtained, giving together with the bulkheads a graphi- 

 cal representation of the safety of the ship in damaged condition. 



In Plate 54 such curves are given for one of the ex-German ships used as a 

 troop transport during the war. The lower curve corresponds to the full load, the 

 upper to the light condition. 



All floodable-length curves are characterized by a maximum amidships, a mini- 

 mum on about one-quarter of the length from each end, and a pronounced rise 

 towards the ends of the ship. 



The floodable-length method, being applicable to all sizes and types of vessels, 

 cannot, of course, be expected to give accurate results in any specific case. Nor is 

 this claimed for it, but, used intelligently, it affords a valuable means of dealing in 

 a practical and comparatively simple manner with problems relating to the spacing 

 of bulkheads. It enables the naval architect to judge whether a given ship is suit- 

 able for use as a troop transport and to determine what alterations, if any, should 

 be made in it to improve the safety. It was applied to all vessels used as trans- 

 atlantic troop transports by the United States Navy during the war and showed 

 that all the ex-German ships when in the light condition were two-compartment 

 ships, many of them with an ample margin, and some approached or reached the 

 three-compartinent standard. In the full-load condition most of those vessels came 

 up to the two-compartment standard. 



3. Changes in the Subdivision of Existing Ships. — In cases of emergency ships 

 may have to be used which are far from satisfactory in point of subdivision, but it 

 must be borne in mind that other qualities have also to be considered. High speed 

 and good maneuvering capability, which materially reduce the dangers of attack by 

 submarines, may outweigh defects in subdivision. A well-subdivided but slow ves- 

 sel may be more exposed to destruction by submarines than a poorly subdivided but 

 faster vessel. Also the accommodations immediately available in a ship for carry- 

 ing troops have to be considered. 



If the subdivision of an existing ship is found unsatisfactory, conditions may 

 be often materially improved by carrying one or more bulkheads up to the deck next 

 above the bulkhead deck. This appUes in particular to ships where non-watertighl 

 bulkheads, which can be readily made watertight, exist above the bulkhead deck as 

 extension of some of the main bulkheads. The addition of one or a small number of 

 new watertight bulkheads and slight modifications of bulkheads already existing 

 above the bulkhead deck will be then sufficient to raise the bulkhead deck for the 

 whole or part of the length of the ship, and the safety may be thus immensely in- 

 creased. In some cases the subdivision below the bulkhead deck may with advan- 

 tage be supplemented by additional bulkheads. Alterations of this nature were made 

 by the Bureau of Construction and Repair' in a number of transports, but on account 

 of the urgency of the service and the short stay in port of the vessels no extensive 

 changes could be carried out. 



