138 BUOYANCY AND STABILITY OF TROOP TRANSPORTS. 



BUOYANCY. 



Under this head we discuss the spacing of the transverse main bulkheads with 

 special regard to the danger of foundering by bodily sinkage, eventually combined 

 with longitudinal inclinations, which may cause the ship to go down by the bow or 

 the stern. We disregard the presence of longitudinal bulkheads and the transverse 

 inclinations which they may produce. 



I. Mode of Procedure. — In case of ships for which all the design data, as well 

 as the conditions of loading, are accurately and completely known, the problem is 

 relatively simple. The effects of bilging on draught and trim can be calculated by 

 direct methods, all combinations of flooding of two or more compartments in ac- 

 cordance with the stipulated requirements being studied. There is, in fact, nothing 

 in the problem which calls for an explanation beyond that already given in text- 

 books on naval architecture. The difficulties arise when it is required on short 

 notice to equip and use, for transport service, ships such as ordinary transoceanic 

 steamers about which only incomplete information is at hand and where circum- 

 stances do not allow time or opportunity for complete calculations. Such were the 

 conditions in case of many passenger steamers taken over in 19 17 by the United 

 States Navy for use as troop transports, especially the German vessels, for which 

 in general no line drawings, general arrangement plans, or weight statements were 

 available. In all such cases it is necessary to resort to approximate methods of in- 

 vestigation. 



Specific problems as to the effect of flooding of certain compartments may be 

 solved directly by rough calculations, using approximate methods. In the Levia- 

 than, for instance, it was found that flooding of all four engine-rooms together 

 with adjacent side compartments would produce a bodily sinkage of about. 4 feet 

 and a total change of trim by the stern of 14^ feet. In the Mount Vernon a simi- 

 lar state of bilging would produce a sinkage of 3^ feet and a total change of trim 

 by the stern of 1 1 ^4 feet. This mode of investigation, however, cannot be applied 

 with advantage to all possible cases of flooding of one or more compartments in a 

 ship, because it would involve an amount of labor that would hardly be warranted 

 in view of the crudeness here assumed of the available data. A more general 

 and simple method is needed when it is required to deal with a great number of 

 ships in a short time, in which case broad, comparative results are of more interest 

 than absolute quantitative values. 



2. The Floodable-Length Method. — We shall here briefly describe the so-called 

 "floodable-length" method devised by the Committee on Subdivision of Merchant 

 Ships, appointed by the British Board of Trade.* This method enables a designer 

 with relatively small work to study the spacing of the bulkheads in a new ship with 

 a view to the fulfillment of given requirements as to subdivision, and provides a 



*The provisions of the International Convention for the Safety of Life at Sea relating to Safety of 

 Construction of Ships are in substantial agreement with the results of the investigations of the Board of 

 Trade Committee, which made its report in November, 1914. 



