408 Air-tight Subdivisions in Ships 



closed and air-tight by the pressure of the air within. But 

 inasmuch as the smallest leak of air, whether through the deck 

 or through the bulkheads, would represent an equivalent of 

 water entered and of buoyancy lost, it is necessary to be able 

 to make good the loss by mechanical means. The more care- 

 fully the decks and bulkheads have been fitted in the first 

 instance, the less will be the amount of air which will be 

 required to be supplied by engine or man power in order to 

 keep the water out in the event of serious damage to the ship's 

 bottom. 



Dealing with leaks in this way is equivalent to transferring 

 the leak from the ship's bottom to her deck, and dealing with 

 it there in the shape of an escape of air in place of an entrance 

 of water. 



In order to make successful use of this method it is necessary 

 that the ship's deck and bulkheads should be not only air-tight, 

 but also sufficiently strong to resist a pressure which, in the 

 case of even the largest ships, would not exceed one atmo- 

 sphere, or 15 pounds per square inch. Each compartment 

 would have to be about as strong as an old low-pressure marine 

 boiler. 



Modern men-of-war are built in such a way that they 

 require nothing but the air-tight hatches, and air-forcing 

 pumps to make them quite secure against the most extensive 

 damage to their bottoms. Indeed, as regards the stoke-holds, 

 they are already fitted with the air-tight hatches in order to 

 be able to use forced draught for the furnaces. Modern 

 merchant ships are built with an iron deck, so that there is no 

 difficulty about providing the strength. Their hatchways are, 

 however, always very large; but, on the other hand, there is 

 little traffic through them, so that they could be treated in a 

 more substantial way than the smaller hatchways of a man-of- 

 war with her large complement of men. The bulkheads which 

 subdivide the hold into compartments always profess to be 

 water-tight, and to be able to resist the pressure exercised by 

 the water filling the compartment. There should therefore be 

 no difficulty about them. Indeed, if ships were built to with- 

 stand air pressure, a very simple method would be provided 



