STEAM PROPULSION. - Relative to steam propulsion, the New York Herald, in a recent editorial says: The new steam launch Arrow, lying at the foot of Court street, Brooklyn, has be recent experiments, developed the fact that she is possessed of that great phenomenon known in shipbuilding as "negative slip," viz.: running faster than the pitch of the screw and its revolutions call for. The first instance in "negative slip" was discover upon completion of a man of war for the British Government, some ten years ago. It was set forth in the specifications that a screw with a certain pitch should be provided for the vessel; that the engine should turn the screw a certain number of revolutions per minute, and also that the vessel should possess a certain speed.
Upon her trial trip the government officer found that the specified number of turns were not made by the engine, but that the speed of the ship was considerably faster than the contract required. The vessel was paid for after further tests and then a great deal of discussion arose between boat builders and engineers to what should cause the vessel to run faster than the screw. The theory was finally arrived at that while sailing the ship dragged the water after her at the rate of about two miles per hour, and when the screw came towards it it possessed, like other screws, "positive slip," but the speed being less than the "drag" of the ship, the remarkable feature of the "negative slip" was produced. The launch Arrow was built and is owned by Capt. Hatfield. The pitch of her screw is 38 inches, and make 200 turns per minute. If, instead of pitching forward, the screw slipped back 30 per cent, as is the case with other small boats, her speed would only be 5 2/100 miles per hour. But the fact has been determined that her screw slips forward, as in the British man of war. On a recent test the Arrow made two and a half miles in seventeen minutes with the tide, and the same distance in twenty minutes against it. This gives her seven and a half miles per hour of speed which, when 200 turns are made, places it at eight miles per hour. Should the secret of "negative slip" be definitely arrived at, great improvements in steamship sailing may be looked for.