150 



BUOYANCY AND STABILITY OF TROOP TRANSPORTS. 



method was actually used in the transports under the control of the United States 

 Navy during the war and afforded a ready and valuable means of controlling the 

 loading and ballasting. In fact, observation of the period at sea was the only avail- 

 able method by which it was possible to obtain a knowledge of the stability in the ma- 

 jority of cases. The following table gives the observed period of roll and the mean 

 draught for a number of typical ships in full-load and light conditions, that is, at 

 the beginning and end of the round trip. 



Table III. — Periods of Roll at Sea. 



Ship 



Leviathan ex. Vaterland 



George Washington 



Mount Vernon ex. Kronprinzessin Cecilie 



President Lincoln 



Covington ex. Cincinnati 



Louisville ex. St. Louis 



.i^olus ex. Grosser Kurfiirst 



Pocahontas ex. Prinzessin Irene 



Great Northern 



Calamares 



Orizaba 



After leaving U. S. 

 Full load 



D 



Feet Inches 



40 11 



35 

 34 

 32 

 30 

 30 



26 11 



26 9 



26 8 



24 4 



24 



Seconds 



11.0 

 8.0 

 9.0 

 8.7 

 8.1 

 7.7 

 6.5 

 6.0 

 7.4 

 9.0 

 7.0 



Before arriving U. S. 

 Light 



Feet Inches 



36 8 



28 5 



26 

 24 3 

 24 6 



27 9 



22 9 



23 3 

 21 8 

 19 6 

 18 3 



Seconds 



13.0 



11.0 



11.0 



6.7* 



9.9 



8.2 



9.0 



7.5 



7.8 



11.3 



11.0 



4. The Loss of Stability by Bilging and the Residual Metacentric Height. — 

 The effects of bilging on stability may be studied by calculating the change in meta- 

 centric height and the angle of heel by approximate methods. In ships subdivided 

 on the purely transverse system it is sufficient to determine the change in meta- 

 centric height, assuming that two or three of the largest compartments are flooded, 

 according as the ship is required to come up to the two or three-compartment stand- 

 ard respectively. In order to obtain the severest case, it may be necessary to repeat 

 the calculation for several combinations of flooded compartments. Using the lost 

 buoyancy method, by which the center of gravity remains fixed in position, the 

 change in metacentric height, MM,, is the algebraic sum of the vertical movement of 

 the center of buoyancy, BBi, which is always positive, and the change in meta- 



st 



centric radius, which is always negative, and approximately equal to -^ , where i 



♦President Lincoln, in the light condition, carried 2,400 tons of steel ballast, 2,200 tons of water, and 

 1,700 tons of coal. 



