134. TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE  [VOL. XI. 
per H.P.-hour, 7.e., less than any other source of energy at present 
available for this purpose. 
Attempts have been made to introduce accumulators of different 
type but so far without success. The Edison alcalic iron-nickel cells 
are about 10 per cent. lighter, but occupy at least 25 per cent. more 
space; they cannot be so rapidly discharged as the lead accumulators. 
They cost more than three times as much, but are more durable. It 
appears that recently improvements have been made and better results 
are claimed by the makers. Practical service tests are required to 
determine the relative merits of these cells. 
The total energy accumulated by storage batteries is necessarily 
small and rarely allows more than a speed of about Io kts. for 3 or 4 
hours. Recently boats have been designed for 11 or 12 kts. The radius 
of action at maximum speed of large boats is about 30 or 40 miles, at 
reduced speed about 100 miles. 
The excessive weight of the plant for underwater propulsion is the 
more unfortunate, since the weight available for propulsion is already 
very small as compared with that in ordinary torpedo-boats. The 
reason for this is that the hull weight is extremely great, occupying 
about 20 per cent. more of the total displacement than in an ordinary 
torpedo-boat. Only about 30 per cent. of the displacement of a sub- 
marine boat can be devoted to machinery and fuel as against about 
50 per cent. in a torpedo-boat. Moreover the plant for underwater 
propulsion comes as an extra addition. It is evident, therefore, that 
submarine boats can never compete with torpedo-boats as to speed and 
radius of action. 
Great efforts are being made to devise a type of machinery that can 
be used both on the surface and submerged and especially one by which 
the propulsion under water does not entail any extra weight, but no 
satisfactory solution has yet been obtained. Any process based on 
combustion involves the storage of atmospheric air or oxygen, but a 
storage of these gases in sufficient quantities for underwater propulsion 
requires excessive weight and space. The discharge of the products 
of combustion is liable to reveal the presence of the boat. 
M. d’Equevilley has proposed a solution which is being tried in the 
French submersible Charles Brun and probably also in a German boat.* 
He uses an ordinary boiler with oil fuel and a steam engine on the sur- 
face, but when the boat dives under water the exhaust steam is led to 
a concentrated lye of sodic hydrate (NaHO) which absorbs the steam 
under strong evolution of heat and thus serves as fuel in a secondary 
‘soda boiler’. This process goes on till the lye is saturated. When 
* Jahrbuch der Schiffbautechnischen Gesellschaft, 1913, pp. 131-138. 
