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back, it is probable that they would be available at sea in rough weather when the boat built only for speed would hardly be safe.
There are two drawbacks to the use of existing torpedo boats for which various remedies have been proposed. The first and most serious is the discharge of smoke and sparks through the funnel which make known the vessel's presence to the object of attack. The second is the difficulty of steering with the ordinary rudder at the very high speeds obtained. In a recent boat built for a foreign Government, Messrs. Yarrow attempted to remedy the first defect by discharging the smoke through side ports, the side being used which was farthest from the enemy, and the port having valves which are kept open by the blast and closed by any large wave. The arrangement was only available in fine weather, and a temporary funnel had to be rigged on other occasions. The same boat has also, in addition to the rudder aft, a rudder placed about 10 feet from the bow, both being worked simultaneously by connection with the same steering-gear.
The forward rudder can be raised within the vessel when she is going at her low speed and when it is not required. It is said that on the trial of the boat, it was found that at high speeds the forward rudder was more useful in steering the boat than the after one. Another novel design was the Herreshoff torpedo boat, built last year for our Government by a company of that name at Rhode Island, U.S.A. Her engines are in the fore part of the vessel and by means of an inclined shaft, which for most of its length is below the keel of the boat, turn a propeller which revolves entirely below the keel, and in the midship part of the vessel. The rudder is aft and is also entirely below the keel. The boat can be propelled a-head or a-stern with equal speed and steers well. With two torpedoes on board, the total weight including fuel and crew of four men is 7 tons. attained on trial a speed of 16 knots. The Herreshoff boat is 591 feet long, 74 feet beam, and 54 feet depth, of which more than 4 feet is above water. She is covered in above with t'o-inch steel plates, but her bottom is planked with wood on steel frames and with five steel watertight bulkheads. This boat has a special kind of boiler, consisting of two continuous coils of pipes enclosing the combustion chamber. It is said that steam can be got up in five
earlier boats in the French Navy were designed to be armed with spar torpedoes ; those of the last type built in France are to carry the Whitehead, and are of 33 tons displacement, and 92 feet long, with a speed of 19 to 20 knots. The plates are of steel, and are said to be three to five millimetres (roughly two to threesixteenths of an inch) thick.
Our own Government has been blamed for not having gone in for torpedo boats more extensively and at an earlier date. They were certainly rather behind hand in adopting the new engine of naval warfare, but we think that possibly they were, and are right in exercising some caution as to the amount of money to be spent apon vessels which may be superseded in a few years by others, perhaps faster and more efficient. The mere fact that Russia in so short a time got together so large a number as a hundred would indicate that this branch of the Navy is one in which we may to some extent trust to our great facilities for rapid increase when the boats are likely to be required. In this regard it is worthy of note that the large majority of torpedo vessels, of all sizes, have been built in England.
Large ironclads take years to build, and no amount of money can in an emergency make up for lost time, as far as they are concerned, but, as regards the small torpedo craft, it would appear to be the wisest course to increase their numbers gradually, thus acquiring experience as to the respective capabilities of various classes of boats. It must also be remembered that these vessels are of necessity comparatively short-lived. They trust to their high speed for safety in presence of a heavily-armed enemy, who has difficulty in hitting a rapidly moving object, and high speed is obtained by cutting down the weight carried to a minimum-hence the plating is of necessity so thin that a very small amount of deterioration tells heavily upon it.
It is difficult, in the present state of our knowledge, to estimate the relative importance of the torpedo boat in naval wars of the future. In the defence of harbours it, in combination with submarine mines, will doubtless be largely used, but in a great battle on the high seas our present experience would appear to indicate that the big gun and the ram will both be more important weapons than the torpedo.
apwards or downwards. The heeling deviation is, in this case, to the high or weather side, whether heeling to starboard or port.
Since, however, the effect of induction will be changed at the magnetic equator, and will be reversed, as the upper end of the iron acquires magnetism south of the equator, the heeling error, to state a general case, arises from the following causes :
1. Vertical induction in transverse iron, which draws the N. end of the needle to windward in N. latitudes, and to leeward in S. latitudes.
2. Vertical force arising from sub-permanent magnetism; and vertical induction in vertical iron; which, in the usual position of the steering (aft) compass, draws the N. end of the needle to windward in ships built head North, to leeward in ships built head South.
Hence, an iron ship, built head North, will generally have a large heeling error to windward in N. latitude; and a small heeling error, which may be to windward or to leeward, in S. latitude.
Also, an iron ship, built head South, may be expected to have a small heeling error to windward or to leeward in N. latitude, and a considerable heeling error to leeward in S. latitude.
The heeling error being a maximum on the North and South points by compass, and nil at East and West, it is evident that the coefficient C is that which must be most affected, and if the deviation for an upright ship be,
d = B sin u + C cos z + D sin 2 % we shall have, for a ship heeling n degrees, with c taken to be the change in C for one degree of heel, the following formula
= B sin z + C + c no) cos 2 + D sin 2 % or, dn = d+ c no cos z that is, the heeling error alters proportionally to the number of degrees of heel and the cosine of the azimuth of the ship's head.
It is possible to put this, for practical purposes, in a more simple form. Since, in the northern hemisphere, in the majority of iron ships, the North end of the compass needle is drawn to windward (to the weather, or high, side) when the binnacles are above