68 STABILITY OF VESSELS AS AFFECTED 



In the preliminary stages of the design, an approximation of the weight and 

 vertical center of gravity of each of these items may be made, and the results com- 

 bined, in order to get an approximate figure for the height of the center of gravity 

 of the loaded vessel. An inclining experiment made on the vessel when completed 

 will serve to eliminate uncertainty as to some of the items, generally the first three. 

 The last three items are variable quantities, and must be figured, at best. It has 

 been proposed to determine the metacentric height of vessels before each voyage 

 by inclining them as soon as the cargo is on board. Experience in inclining vessels 

 at a shipyard indicates that the results would not be likely to be reliable, as the 

 readings are affected so greatly by loose water and moving people. Greater accu- 

 racy is likely to be obtained by determining beforehand how much weight of cargo 

 is to be stowed in each division of the vessel in order that the center of gravity of 

 the cargo may not exceed a certain height above base, considered desirable in order 

 to obtain a predetermined minimum metacentric height under the most unfavor- 

 able conditions of bunkers likely to occur on the voyage. 



This leads up to the question: What is the minimum metacentric height for 

 any vessel consistent with safety? The question is susceptible of several answers, 

 depending on whether the vessel is considered as intact and exposed to storm and 

 waves, or as "damaged" either in still water, in a moderate sea, or exposed to 

 storms. 



In general, it may be stated that passengers prefer a vessel with a long period 

 of roll, as the discomfort is much reduced thereby. To obtain a long period it is 

 necessary to have a large vessel or a small metacentric height; and the combina- 

 tion of the two requisites in the large Atlantic liners renders travel on them a pleas- 

 ure instead of a bugbear to the landsman with a "sympathetic" stomach. If the 

 small metacentric height is accompanied by a high freeboard and a considerable 

 range of stability, there is small danger of capsizing, due to wind and waves, while 

 "intact." This "comfortable" condition of a vessel, however, may be a source of 

 great danger even in still water if the vessel is damaged by collision. 



To illustrate the conditions obtaining, a coastwise passenger steamer 370 feet 

 long, 49 feet 6 inches beam, and 35 feet deep to hurricane deck, has been selected. 

 The vessel is considered as subdivided in accordance with the regulations proposed 

 by the International Convention on Safety of Life at Sea of 1913-14, as a vessel 

 engaged in a mixed cargo and passenger service. The load draught allowed with 

 bulkheads extending to the main deck (the lowest point of which is 26.92 feet 

 above base) and with machinery compartment 65 feet in length, is 21.7 feet. At 

 this draught it is assumed that the cargo is so loaded that the metacentric height 

 is 6 inches. The range of stability, as shown on Fig. i, Plate 18, figures out at 82 

 degrees, and the maximum righting arm is 1.9 feet at 48 degrees inclination. It 

 would be a pleasure to sail on this vessel under such conditions. 



Now let us suppose that the machinery compartment is opened to the sea by 

 collision, that the permeability of this compartment is .80, that the water surface in 

 the damaged compartment at all stages has an inertia coefficient of .80, and that 



