668 Transactions. — Miscellaneous. 



of a ship's cargo, even though her draught of water remains 

 the same. This is because the height of her centre of gravity 

 will thereby be altered. It is also evident that the buoyancy 

 varies with any increase or decrease in the mean draught 

 of water, or from an alteration in trim — i.e., in the draughts 

 of water forward and aft respectively. A variation in the 

 position of the centre of buoyancy results from these latter 

 changes. It therefore follows that, as a vessel on a long 

 voyage consumes water, stores, or coal, she alters both elements 

 which determine her stability. Her centre of gravity is altered 

 in position by the change in her lading, and her centre of 

 buoyancy by the reduction in her mean draught of water, 

 while it is more than likely that she has risen more at one end 

 than at the other. A responsibility, therefore, rests not only 

 with her designer to consider these possible changes and 

 provide for sufficient stability under the worst of ordinary 

 conditions, but with the captain also, who should obtain some 

 scientific knowledge of her peculiarities, so that he may stow 

 the cargo in such a way as to prevent the occurrence of any 

 extraordinary conditions. 



The main explanations of the principles of stability have 

 now been made ; but I wish to refer to and explain three 

 assumptions wdiich it seemed desirable to make with the 

 object of simplifying for the moment certain portions. The 

 first one made was in dealing with the centre of gravity, and 

 was as follows: "It will be necessary to assume that no 

 considerable part of her fittings or lading shall break away and 

 fall to leeward when she is careened." This reservation was 

 necessary to the explanation as it was given, and to the state- 

 ment that the centre of gravity did not alter its position by 

 reason of a vessel being careened. The fact of cargoes being 

 shifted by stress of weather, however, is not by any means 

 uncommon. Again, the presence of a large quantity of water 

 in the bilges may seriously affect stability, and the same result 

 will follow if a water-ballast tank is only partially filled. It 

 is not beyond our power to calculate the effect of any such 

 change of condition as may be supposed to take place. The 

 caisson for closing the entrance of a graving-dock is made to 

 sink into its place by the admission of water into certain 

 compartments. It would not be safe, however, to admit 

 water into such a structure except into limited watertight 

 compartments. In the absence of divisions, the* water by 

 its movements would cease to act as ballast, and would become 

 a source of great danger to the stability of the caisson, and 

 probably cause it to do damage to its own structure and to 

 that of the dock. 



The second assumption was in reference to the buoyancy 

 of a vessel remaining intact after she was careened, and read 



