6o8 



NATURE 



[A^rt/ 2$, 1889 



I shall be obliged if those who have opportunities of examining 

 banks of dry and fine sand inclined at 31° will report through 

 your columns whether they yield deep sounds when disturbed. 



Cairo, April 10. H. Carrington Bolton. 



AIR-TIGHT SUBDIVISIONS IN SHIPS. 



'T*HE last two months have been unfortunate ones for 



■»■ shipping generally, and more particularly for the 

 navies of at least four of the great powers. France has 

 lost two torpedo boats under such circumstances as to 

 involve the condemnation of a whole class of vessels. 

 Germany and the United States of America have each 

 lost a small fleet in a hurricane of unusual violence. 

 Besides the material loss of ships these three nations 

 have to bemoan the loss of a considerable number of 

 men. Only little more than a month ago one of the 

 largest ships of the British Navy stranded in waters 

 rightly assumed to be perfectly safe, and has become a 

 total wreck. Fortunately in this case there was no loss 

 of life. Another of her H.M. ships only just escaped 

 the disaster which overwhelmed the German and 

 American fleets at Samoa, and the circumstances attend- 

 ing her escape are worthy of a moment's attention. 



The storm approached not without warning, and it is 

 evident that the captains of all the ships set about 

 making preparations for meeting it as best they might. 

 They appear all to have got up steam, so as to ease their 

 cables by steaming to their anchors, in case it should be 

 impossible to get out. The only ship that did get out 

 was H.M.S. Calliope, and without in any way detracting 

 from the merits of her captain and those under his orders, 

 it is evident, from the brief accounts to hand, that all 

 would probably have been unavailing had she not been 

 provided with very powerful machinery. In the Navy 

 List her tonnage is given as 2770, and her horse power as 

 4020, or one and a half indicated horse power per ton 

 of displacement. The most powerful of the other ships 

 was the German corvette Olga, which apparently had 

 considerably less than one horse power per ton of 

 displacement. 



The other ships, especially the American ones, were so 

 deficient in power that they were unable to make any 

 front to the storm at all. Even with her great power the 

 Calliope was only able to attain an effective speed of half 

 a knot per hour in the teeth of the storm. All praise is 

 due to the men who were able to make such good use of 

 this very meagre margin as to have saved a costly ship 

 and many valuable lives for the further service of their 

 country. 



The Samoan disaster has thus, in a dramatic and even 

 tragic vvay, shown the uses of steam power in saving a 

 vessel by propelling her against a storm. Reflections on 

 the loss of the Sultan lead us to ask if steam power 

 cannot be made more useful in succouring and saving a 

 ship after she has struck a rock, or in any other way 

 received such damage to her hull as to render her loss 

 by foundering imminent. 



According to convention an engine is working at the 

 rate of one horse power when it is lifting a weight of one 

 ton against gravity at a velocity of 1474 feet per minute. 

 If, then, a ship is fitted with engines indicating one horse 

 power per ton of displacement, these engines would, if 

 their whole power could be usefully appHed and directed 

 against gravity, be able to keep the ship afloat so long as 

 she did not sink at a greater rate than 1474 feet per 

 minute. The Vanguard took seventy-two minutes to 

 sink. The practical question comes to be, How can the 

 ship's power, of engines or men, be best applied so that 

 the greatest proportion of it may be made available for 

 keeping her from sinking ? 



Hitherto it has been usual to fit all ships with suction 

 pumps, capable of being worked, some by steam and some 

 by hand power. To use such pumps with effect it is 



necessary that they should be worked at such a rate as to 

 throw overboard more water than can enter the ship in a 

 given interval of time. The lower they bring the water in 

 the hold of the damaged ship, the greater is the facility 

 offered for the water to enter, and the harder becomes the 

 work of lifting it. If the damage to the ship's hull is in 

 any way serious, cfealing in this way with its effect is 

 almost always hopeless, unless it is possible to get at the 

 leak and reduce its dimensions or close it altogether. The 

 bottom of a ship at sea is very inaccessible. If she re- 

 mains fast on the rock it is usually impossible to get at 

 the leak either from the outside or from the inside. If 

 she is afloat, and will keep afloat long enough, the leak 

 can often be efficiently dealt with by passing a tarpaulin 

 or sail under her bottom. But this is by no means a 

 simple or easy operation, even when performed as a matter 

 of drill with plenty of time, and in the absence of excite- 

 ment or danger. 



When a ship is sinking, she does so because water has 

 got into her either from above or below, and has displaced 

 the air with which she was charged. In order to stop 

 her sinking and to raise her to her original level, it is 

 necessary to reverse the operation and replace the water 

 again by air. If the water has come in from above, by 

 shipping seas, this can be effected by suction pumps, 

 which throw it overboard again. If it has entered and is 

 entering through a hole in the bottom of the vessel, it is 

 necessary not only to remove the water which has entered, 

 but to stop any further entry, and this is achieved by anj 

 means which enables us to thrust the water out again by 

 the same way as that by which it entered. 



If we consider a ship's hold, and assume that the deck 

 covering it above, and the bulkheads shutting it off fore 

 and aft, are all sufficiently strong and air-tight, then, if 

 the whole bottom were allowed to drop out, her stability 

 being otherwise assured, she would be very little the worse ; 

 the water would rise in her hold only until it had so far 

 compressed the air that its tension exactly balanced the 

 pressure of the column of water outside, and matters 

 might safely remain in this condition of equilibrium 

 almost indefinitely. Thus, by making the main deck of 

 a modern ship, to which the water-tight bulkheads are 

 carried up, air-tight, she would be practically proof 

 against all risk of sinking from damage to her bottom. 



I do not think that there would be any difficulty in 

 making the compartments of a ship perfectly air-tight, 

 or more properly, in fitting them so that the rise of ten- 

 sion quickly produced by the entry of water through a 

 serious leak, would at once close any joints or small 

 openings, in the same way as the door of the air lock giving 

 entrance to a submarine caisson is kept 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 carefully 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 trans- 

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

 dealing with it there in the shape of an escape of air in F 

 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 pres- 

 sure which, in the case of even the largest ships, would 

 not exceed one atmosphere, 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 



