BUOYANCY AND STABILITY OF TROOP TRANSPORTS. 139 



ready means of determining the status in this respect of an existing ship, giving a 

 measure of its safety as well as suggestions for eventual alterations in the water- 

 tight subdivision. 



In principle the method consists in determining the "floodable length" at any 

 point in a ship, being the length of hold, having its center at that point, which can 

 be flooded without the ship foundering. The spacing of the bulkheads is expressed 

 as a fraction of the floodable length obtained by multiplying it with a "factor of 

 subdivision." If that factor is everywhere equal to or smaller than unity, but still 

 greater than one-half, any one but not any two compartments may be flooded with- 

 out the ship going down, and we have what is commonly called a "one-compart- 

 ment" ship. If the factor is everywhere equal to or smaller than one-half but still 

 greater than one-third, any two but not any three adjoining compartments may be 

 flooded without the ship going down, and we have a "two-compartment" ship and 

 so forth. 



The floodable length is found as described in Vol. I of the Report of the Com- 

 mittee, while Vol. II gives a number of diagrams from which it may be obtained 

 directly, expressed as a percentage of the length of the ship. The so-called "mar- 

 gin line" forms the basis of the calculation. It is drawn 3 inches below the deck- 

 at-side line of the bulkhead deck, the latter being defined as the uppermost con- 

 tinuous deck to which all transverse watertight bulkheads are carried. The flood- 

 able length is so determined that, when that length of the hold is flooded, the ship 

 shall not be submerged beyond the margin line. 



Various elements are used as arguments in the diagrams of Vol. II for finding 

 the floodable length, the most important being the freeboard ratio, which is the ratio 

 between the freeboard to the margin line amidships and the draught amidships. 

 Greater freeboard at the ends is taken into account by the sheer ratio, which is the 

 ratio of the sheer of the margin line at the forward or after end to the draught 

 amidships, the sheer being measured from the horizontal line through the lowest 

 point of the margin line. The element next in importance is the permeability, which 

 is the percentage of a given space, that can be occupied by water. When a ship is 

 in the light condition, the high permeability of the empty hold spaces to some extent 

 neutralizes the favorable eiTect of the greater freeboard, but nevertheless the flood- 

 able length is ordinarily much greater than in the full-load condition. Exceptionally 

 the floodable length in the light condition may fall below that in the full-load con- 

 dition at the ends. The numerical value of the permeability should be calculated 

 very carefully, as it exerts a great influence on the result. The diagrams in Vol. 

 II of the Report are prepared for permeabilities of 60 and 100 per cent. The flood- 

 able length for other permeabilities must be obtained by interpolation. The form of 

 the hull is taken into account by using the block coefficient as one of the arguments 

 in the diagrams, which are calculated for a standard form of various degrees of 

 fineness. If ships differ materially from the standard form, certain corrections 

 must be applied. 



When the floodable length is obtained for a number of stations in a given ship 



