The general type of hull is the same as that of the Yarrow and Thornycroft, except that it is of composite construction, having a steel frame with wood planking below water and steel above. The propeller is a single two-bladed screw, placed under the keel just abaft the middle of the boat, the hollow steel screw-shaft being put in on a curve. The rudder is of the balanced type, and is suspended underneath the after-part of the keel. The pilot-house is abaft the smoke-pipe. The boiler of this boat is of a novel character. It consists of a cylindrical combustion chamber about 4 feet in diameter, within which is a spiral coil of about 300 feet of two-inch pipe. 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 part 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. By means of this boiler a good working pressure can be obtained in about five minutes from the time of lighting the fires. This boat may be rigged to carry either the Whitehead or the spar torpedoes. Its speed is about 18 knots, equal to that of the Thornycroft. [Illustration: Herreshoff Boiler.] SHIPS’ BOATS. Steam-launches are at present, as a rule, fitted with spar or Whitehead torpedo-gear of a general and simple type. It is not intended that these boats should be classed as fighting torpedo-boats, as they lack the requisite speed and protection, and, as a rule, are too noisy to be of use except in a general or concentrated attack. Such boats find their greatest sphere of usefulness in clearing channels of obstructions and countermining. For the former work many are now provided with electrical valve-gear and steering apparatus, by which they may be controlled from a boat towed some distance astern, as in the manipulation of the Lay torpedo. SUBMARINE BOATS.