the deflective strengths are in the relation of 5^ to 4^, that is, 1-56, and 

 those of buckling of 5 3 to 4^, that is, i -95 ; now the buckling of a part 

 of the metal plate is one of the principal dangers for the float. The fact 

 that resistance to buckling is practically doubled when we pass from 

 2-5- in. to J in. appears to justify the increase in weight of the hull 

 (nearly a ton). 



Appendix 6 



The Keels 



BILGE-KEELS 



A conventional ship is provided on its underwater hull with a keel 

 which makes it easier to maintain its direction and which, in particular 

 in a sailing vessel, resists drifting, and which also damps rolling motions, 

 that is to say, the oscillation of a boat about its longitudinal axis. 

 In order not to increase its draught unduly, keels are also placed under 

 the hull, laterally away from the centre. All these arrangements have a 

 disadvantage: if a wave strikes the lateral keel, the resulting force 

 applies a movement to the ship and thus a certain rolling is produced ; 

 if the swell displaces the ship laterally, the keel placed under the ship 

 and supported by the motionless water also produces rocking. If these 

 disadvantages could be avoided while keeping the favourable action 

 of the keel, which in any case damps out the rocking after it is produced, 

 it would be ideal. The cylindrical float of the bathyscaphe presents this 

 possibility. In fact the petrol which is contained in it does not partici- 

 pate, so to speak, in the rolling: the hull turns round the petrol. If 

 therefore we fix blades within the hull, these, to begin with, will 

 necessarily damp out the rolling by tlieir friction with the petrol and 

 also, being removed from the action of the waves, will not be able to 

 cause rolling. 



Fig. 20 shows the arrangement of these interior anti-rolling keels, 

 which, removed from the attack of the waves, can be made in relatively 

 thin metal-sheeting and thus have the advantage over external keels of 

 an appreciable economy in weight. 



During our operations off Capri, the beneficial action of these keels 

 was remarkable, the Trieste proving much more stable than another 

 vessel of superior tonnage. 



[ i<34] 



