BUOYANCY AND STABILITY OF TROOP TRANSPORTS. 141 



4. Spacing of Bulkheads in New Designs. — The claim stipulated above, that a 

 troop transport should be able to stand the effect of one underwater explosion, de- 

 termines the two-compartment standard as the minimum requirement, but where 

 the size of a ship allows a higher standard to be reached, the designer should of 

 course take advantage of this fact, even when that standard cannot be maintained 

 throughout the entire length of the ship. 



In determining the spacing, the designer must take into account the probable 

 extent of the damage, the probability of bulkheads being lost, and the effects on the 

 buoyancy. He must consider also the limitations imposed by the size and length of 

 the ship, as well as by the general requirements of the service. We shall take up 

 each of these questions separately. 



(a) The first thing to consider is the horizontal extent of the zone of rup- 

 ture and deformation caused by the explosion of a mine or torpedo, in so far as 

 those effects destroy the integrity of the bulkhead. Its value varies greatly with 

 the size of the charge and with various other conditions, but seems to lie between 

 25 and 55 feet. We shall denote this quantity by e and assume that under present 

 conditions its probable highest average value is 35 feet. This is but slightly smaller 

 than the figure adopted by Mr. W. S. Abell, Chief Ship Surveyor of Lloyd's Regis- 

 ter of Shipping, in a paper read before the Royal Society, January 22, 1919, dis- 

 cussing the same subject for cargo vessels. 



(&) There is for every part of a ship a lower limit to the spacing of the bulk- 

 heads, determined with regard to proper housing and working of the machinery, the 

 service of the ship, the accommodation of the troops, and the stowage and handling 

 of cargo as well as the proper utilization of space in general. In the forward and 

 after holds, excepting the extreme end compartments, the spacing seldom falls be- 

 low 35 feet in practice, and probably 40 feet may be considered as the smallest de- 

 sirable spacing of the bulkheads in those parts of the ship. In the midship por- 

 tion, where the machinery is located, it is often necessary to make the compartments 

 much larger, especially in ships like troop transports which have or should have 

 great engine power. 



(c) If the spacing of the bulkheads is equal to e, the extent of the damage caused 

 by an explosion, it is likely that an attack would always injure at least one bulk- 

 head, but by increasing the spacing beyond this limit even by a very moderate 

 amount, the probability of a bulkhead being lost is very much reduced. Let the 

 spacing be s, then this probability, which we shall call c, is measured by the ratio 

 between the danger space, e, and the remaining space, s — e, in each compartment. 

 Hence— 



^ = — (i) 



s-e 



When J- = ^, we have c = 00, but when s is 20 per cent greater than e, c = 5, 



that is, the chances are only 5 to i that a btilkhead will be lost by a single explosion. 



Based on these considerations it is proposed in troop-transports to adopt a mini- 



