The motive power on the surface is supplied by a triple-expansion steam engine of 250 horse-power constructed by Messrs. Brule and Co. It has a water-tube boiler of the Seigle type having five injectors for stoking with heavy petroleum.
In the original project the boat was to have been propelled on the surface by steam machinery of 300 i.h.p., the stoking being with compressed coal, but it was afterwards decided to supply liquid fuel.
Submerged the motive power is an electro-motor, the current being supplied by 158 accumulators of the Fulmen type, which can be recharged by the motor, worked as a dynamo by the petroleum motor.
Before going below the chimney is to be unshipped and all the openings are hermetically closed. Sufficient time is allowed for the motor to cool and for the air to be cleared of the hot gases. The steam engine has to be replaced by the electric motor and water ballast has to be pumped in.
At first these operations took at least a quarter of an hour, but the newer vessels of the Narval class are said to be able to disappear beneath the waves in some five moments only.
Photo by] [M. Bar
THE “NARVAL.”
The armament consists of four 17½ inch Whitehead torpedoes, and there are two Drzewiecki torpedo tubes on each side and towards the upper part of the boat, which launch the torpedoes in the direction of the beam.
“As long ago as 1893,” says a French writer, “Mr. Drzewiecki invented a method of firing a torpedo which is quite different from the torpedo tubes commonly used, and which is, therefore, peculiarly suited for submarine vessels. By it the torpedo could be fired at any angle from 30 to 120 degrees from the bow, and experiments with it were carried out in 1894 at Cherbourg. The system may be briefly explained as follows: At the side of the boat a horizontal spar is placed, which works on a hinge at an angle to the bow. The torpedo is fastened to this spar by two pairs of clamps, and when not in use lies along the side of the boat in a recess cut in the side. A swing-out rod, fastened at one end to the spar and at the other to the boat, enables the desired angle for firing to be obtained. A lever worked from inside the vessel pushes the spar and the torpedo away from the side of the boat, and the pressure of the water stiffens the swing-out rod, and by so doing frees the torpedo from the clamps, and opens the air lever which sets the torpedo in motion. It is, therefore, necessary that the vessel should be under way when the torpedo is fired.
“The principle of the invention is very simple, and at the same time very ingenious; and the experiments which were made at Cherbourg proved that torpedoes could be fired by this system with perfect precision. Since 1894 Mr. Drzewiecki has made alterations in his invention. For example, he has done away with the spar and the clamps, and by so doing has greatly lightened his apparatus. The tail of the torpedo is now seized by two claws, which grip it firmly and hold it in position. The contrivance is placed on the deck of the submarine boat, which is not submerged except on going into action. The torpedo rests on cushions fixed to the deck, with its axis parallel to that of the boat, but as soon as it is moved by a lever to the position for firing, the water pressing against it frees the torpedo by opening the air valve. The only inconvenience of the system is that it is not easy to fire at the exact angle required, but it has the great advantage of doing away with all the machinery of valves and safety appliances which are necessary when submerged tubes are employed. Further experiments will doubtless make the system still more efficacious.”