This type of torpedo boat attains a speed of from 17-1/2 to 18-1/2 knots per hour.
The armament of some of these boats consists of three spar torpedoes, a bow, and two quarter ones. The bow pole, which is strong and heavy, is hauled out and in by means of a small auxiliary engine.
Boats similar to these, but of larger dimensions, viz. 84 feet long and 11 feet beam, have also been constructed by this firm. Speed from 19 to 20 knots per hour.
English Torpedo Boats.—The following account of two torpedo boats which had been originally built by this firm for the Russian government, but, owing to the proclamation issued by the English government at this time prohibiting torpedo boats leaving England, were seized by the Customs authorities when on the point of completion, and were ultimately purchased by the English government, is an extract from the Times under date the 4th of July, 1878.
"These vessels are each 85 feet long with 11 feet beam, and draw, when fully equipped for service, an average of 3 feet of water. They are strongly constructed of steel, and are fitted with compound surface condensing engines capable of indicating 420 horse power. The high pressure steam cylinder of these engines is 12-1/2 inches in diameter, and the low pressure 21-1/2 inches, both having a 12 inch stroke. These boats are at present known by their builders' numbers, one being No. 419 and the other No. 420. The former is propelled by a three-bladed screw, 5 feet 6 inches diameter and 5 feet pitch; and the latter by a two-bladed screw of similar proportions. Messrs. Yarrow adopt supplementary engines for driving the air pump, circulating pump, and feed pumps; they consider this plan preferable to that of working these pumps direct off the main engine, as is sometimes done. One advantage in having separate pumping engines is that, whether the vessel is in motion or stationary, a powerful means is available for pumping her out, should the necessity arise. It is estimated by her builders that if the air pump and circulating pump were both utilised for this purpose, the water could be pumped out as fast as it could enter either of these vessels through one hundred holes made in the skin by Martini-Henry rifle bullets. If this is the case, these craft may be deemed safe from sinking so long as their machinery is working efficiently. The boiler is of the locomotive type, placed in the forward part of each vessel, and has a closed stoke hole. In connection with the boiler a very important improvement has been introduced by Messrs. Yarrow. This consists in a means of rendering the closed stoke hole safe for the men in the event of the collapse of a boiler tube—a contingency which cannot be absolutely guarded against. Its efficiency was proved beyond all question upon a previous trial of one of these boats. This was No. 419, which was tried on the 24th of May last under the supervision of the Admiralty officials. Upon that occasion an accidental rupture of one of the boiler tubes occurred nearly at the close of the runs over the measured mile, which so far had been very successful. When the boiler tube gave way the steam rushed out of the foremost hatchway from the compartment in which the smoke box end of the boiler is situated, and soon after from the two funnels. The men in the stoke hole, however, being shut off from the boiler, were uninjured, and remained at their post several minutes after the first outburst of steam. The accident, although an untoward event, was considered by the Admiralty officials as affording a highly satisfactory proof of the efficiency of Mr. Yarrow's invention.
"The engines are placed amidships, and each vessel has spacious cabin accommodation aft, as it is intended that they may be used either as despatch or torpedo boats. For the latter purpose the cabin framings above deck are removed and replaced by steel plating. They are steered from the cabin, there being a look-out for the steersman just above deck level. The deck is clear of all obstructions, the two funnels being placed one on either side. They are fitted with balanced rudders and steer well, answering their helms very quickly."
The trials of these two torpedo boats are taken from the Engineer under date the 19th of July, 1878. At that time these boats completely eclipsed in speed everything that had hitherto been done. At [Fig. 160] is shown in elevation this type of torpedo launch.
"The trials were personally conducted by Mr. Yarrow, under the superintendence of the authorities from Whitehall, and consisted in a two hours' run without stopping, during which time the boats were tested at the measured mile at Long Reach. Each boat was run six times over the mile, three runs with the tide and three runs against it. The boats and machinery are similar in every respect, excepting that No. 419 is fitted with a three-bladed propeller, and No. 420 a two-bladed one, their diameters and pitch being the same in both cases. The weights on board were accurately weighed, and amounted to 6 tons in each boat, including coals, water, crew, and ballast.
"Trial of No. 419.
| Min. | Sec. | Knots per hour. | ||
| 1st run down | occupied | 2 | 36 | 23·076 |
| 1st run up | " | 3 | 20 | 18·000 |
| 2nd run down | " | 2 | 35 | 23·226 |
| 2nd run up | " | 3 | 16 | 18·367 |
| 3rd run down | " | 2 | 32 | 23·684 |
| 3rd run up | " | 3 | 14 | 18·557 |