Chapter 3-STABILITY AND BUOYANCY 



Trim by bow usually means a decreased KM. 

 The center of buoyancy will rise slightly, but 

 this is usually counteracted by the decreased 

 BM caused by the lower moment of inertia of 

 the trimmed waterplane. 



CAUSES OF IMPAIRED STABILITY 



The stability of a ship may be impaired by 

 several causes, resulting from mistakes or from 

 enemy action. A summary of these causes and 

 their effects follows: 



ADDITION OF TOPSIDE WEIGHT 



The addition of appreciable amounts of top- 

 side weight may be occasioned by unauthorized 

 alterations; icing conditions; provisions, ammu- 

 nition, or stores not struck down; deck cargo; 

 and other conditions of load. Whenever a weight 

 of considerable magnitude is added above the 

 ship's existing center of gravity the effects are: 



1. Reduction of reserve buoyancy. 



2. Reduction of GM and righting arms due to 

 raising G. 



3. Reduction of GM and righting arms due 

 to loss of freeboard (change of waterplane). 



4. Reduction of righting arms if G is pulled 

 away from the centerline. 



5. Increase in righting moment due to in- 

 creased displacement. 



The net effect of added high weight is always 

 a reduction in stability. The reserve buoyancy 

 loss is added weight in tons. The new metacentric 

 height can be obtained from: 



GjM^ =KM^ - KG^ 



Stability is determined by selecting a new 

 stability curve from the cross curves and cor- 

 recting it for AG^ sine and G1G2 cos e. 



LOSS OF RESERVE BUOYANCY 



ancy is lost. The immersion of buoyant volume 

 is necessary to the development of a righting 

 arm as the ship rolls; if the hull is riddled it 

 can no longer do this on the damaged side, 

 toward which it will roll. In effect, the riddling 

 of the above- water hull is analogous to losing a 

 part of the freeboard, thus reducing stability. 

 When this happens, if the ship takes water 

 aboard on the roll, the combined effects of high 

 added weight and free surface operate to cut 

 down the righting moment. Therefore, the under- 

 water hull and body should be plugged and 

 patched, and every effort should be made to re- 

 store the watertightness of external and internal 

 boundaries in the above- water body. 



FLOODING 



Flooding may take place because of under- 

 water damage, shell or bomb burst below decks, 

 collision, topside hit near the waterline, fire- 

 fighting water, ruptured poping, sprinkling of 

 magazines, counterflooding, or leakage. Regard- 

 less of how it takes place it can be classified 

 in three general categories, each of which can 

 be further broken down, as follows: 



1 . with respect to boundaries 



a. solid footing 



b. partial flooding 



c. partial flooding in free communication 

 with the sea 



2. with respect to height in the ship 



a. center of gravity of the flooding water 

 is above G 



b. center of gravity of the flooding water 

 is below G 



3. with respect to the ship's centerline 



a. symmetrical flooding 



b. off-center flooding 



Reserve buoyancy may be lost due to errors, 

 such as poor maintenance, failure to close fit- 

 tings properly, improper classification of fit- 

 tings, and overloading the ship; or it may be lost 

 as a result of enemy action such as fragment or 

 missile holes in boundaries, blast which carries 

 away boundaries or blows open or warps fittings, 

 and flooding which overloads the ship. When the 

 above-water body is holed, some reserve buoy- 



Solid Flooding 



The term solid flooding designates the situ- 

 ation in which a compartment is completely 

 filled from deck to overhead. In order for this 

 to occur the compartment must be vented as by 

 an air escape, an open scuttle or vent fitting, or 

 through fragment holes in the overhead. Solid 

 flooding water behaves exactly like an added 



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