"Steam is supplied by a Herreshoff coil boiler, which constitutes another novelty in this boat. This boiler consists of a circular combustion chamber, which in the present instance is 4 feet in diameter internally, and within which is a coil of about 300 feet of 2 inch pipe coiled to nearly the diameter of the chamber. This coil is continued at the top so as to form a kind of dome under the cover of the combustion chamber. By the side of the boiler is a separator, into which the steam passes before it goes to the engine. The water from the feed pump is admitted at the top of the coil, and during its course to the bottom the greater portion of it becomes converted into steam. Having passed through the entire length of the coil, the steam and water are discharged together into the separator in such a manner that the water is entirely separated from the steam, and can be blown off as required. The steam is taken from the top of the separator, and returns through a short coil placed inside the combustion chamber, where it becomes superheated, and is led thence to the engines. It is claimed for this boiler that it cannot explode destructively, inasmuch as there is but a very small quantity of water in it at any time, and that it is distributed along the entire length of the coil. A rupture at any point would only be attended by a moderate blowing off of steam. The rapid circulation of the water is found to prevent the deposit of salts, the surplus water not converted into steam carrying with it all impurities. A good working pressure can be obtained within a few minutes of lighting the fire, and the boiler can be blown off in a few seconds. The large combustion chamber enables the full economy of the fuel to be realised."[P]
This vessel is guaranteed for a speed of 16 knots per hour. She can be propelled ahead or astern with equal speed, and can be brought to a dead stop when going full speed within a distance equal to her own length. Her turning powers are equally good. Her armament will probably be the fish torpedo.
_Ordinary Torpedo Boat._--The most efficient and simple method of fitting and working a spar torpedo from an ordinary steam launch or pinnace is shown at Fig. 165. This method will be readily understood from the figure; the dotted lines show the position of the spar and upright, when rigged in. The speed of this type of torpedo boat ranges from 6 to 9 knots. Occasions would no doubt occur in time of war when a torpedo attack by such boats would be a feasible matter, and therefore everything should be done to render these boats fit for that special service.
