wood in the usual manner, viz: Carysfort, Cleopatra, Conquest, Champion, Comus, Curaçoa. The length between perpendiculars is 225 feet; beam, extreme, 40 feet; depth of hold, 21 feet 6 inches; and displacement, 2,300 tons. The material entering into the construction of the hulls will in the main be steel. The principal water-tight bulkheads will be four in number. There will be two decks, and, for the purpose of protecting the ma chinery, the lower deck, for the distance extending over the engines and boilers, will be armored with 14-inch steel plates. The vessels are to be fully rigged as cruisers and to be fitted with single screw-propellers arranged for lifting. The steam-machinery has not been ordered at this date, but the fact has been announced that the engines would be of the compound type, having as great power as the dimensions of the vessel would admit. TRIALS OF BRITISH NAVAL VESSELS AT THE MEASURED MILE. The speed of all steam-vessels belonging to the British navy is tested by running them over a measured mile in Stokes Bay, near Portsmouth. The indicated horse-power of new engines, as stipulated by contract, is also determined on the runs over this course. The noteworthy points in the regulations for these trials are as follows: Her Majesty's ships are to be tried on the measured mile on the following occasions: 1st. After having new engines erected. 2d. After every extensive repair of engines. 3d. On being commissioned when all their weights are on board. 4th. When trials may be ordered on special occasions. duration than four hours. * # * * * * Ships in the first division of the reserve are to be tried under way once every year during summer for not less than six hours; but it is not required that they be taken to the measured mile for the purpose, and their trial at full speed need not be of longer The trials of ships at the measured mile are to be conducted under the charge of the captain or commander of the reserve, who is to be accompanied by the constructor, an engineer officer from the yard, and the chief inspector of machinery afloat. As a rule the trials should not take place when the force of wind exceeds 3. No other coal is to be used while running the mile than the coals specially ordered by the Admiralty. * The best trained stokers that can be selected from the reserve are to be employed. On the full-power trials of ships at the measured mile, the engines and boilers are to be worked to the utmost extent of their capabilities, not only when running the mile, but the whole of the intervals between the several runs. * * # # * * * The In the intervals between the runs, ships are to be run well away from the marks, so as to insure the attainment of full speed on their return to them. Steam must not be partially shut off when the ship is not on the mile in order to obtain a higher result when she is on the mile. Indicator-diagrams are to be taken, as nearly as possible, at equal intervals of time during each run, in order to obtain the real mean pressure in the cylinders. revolutions of the engines during each run are to be taken by the counter. If, during the trial, any defects should occur to the machinery or the ship, the trial is to cease; # a new series of trials being commenced when the defects shall have been made good. If the boilers should prime so that they cannot be worked at full power, even at the close of the trial, it is to be considered as unsatisfactory and the trial is to be repeated. Whenever irregularities occur in running the measured mile, either at full or half power, the officers are to repeat the runs until the results agree one with the other so nearly as to leave no reasonable doubt of their substantial accuracy. When ships which have new engines not yet received from the contractor are under trial at the measured mile, the engines and boilers during the trial are to be under the charge of the contractor or his agent, who is to have the whole responsibility and management; but the trial is to be conducted in strict accordance with the regulations laid down for all trials at the measured mile, and the engineer officers will be responsible that the regulations are never deviated from. Full and detailed reports of the results of the trial of each ship at the measured mile are to be made in the prescribed forms and forwarded to the Admiralty. A tracing of * * the screw-propeller is to be annexed thereto, also a set of original indicator-diagrams for one mile only. In all reports of trials it is to be stated whether the engines and boilers did or did not work in a satisfactory manner, and are or are not in all respects fit for service at sea. If the trial should not have been satisfactory, the reason is to be stated and the time it will take to render the machinery fit for service at sea. When the ship tried is in commission, the reports are to be signed by the captain and chief engineer of the ship, as well as by the officers of the reserve and the dock-yard. After every trial of a ship in commission, and before proceeding to sea, the ship is to run into the harbor for at least 24 hours, and be carefully examined by a shipwright and engineer officers of the yard, to ascertain that there are no defects, and a report made. These reports are to be signed by the dock-yard officers who made the examination, the chief constructor, and the chief engineer of the dock-yard; also by the officer in command of the ship and the chief engineer of the ship, and are to be accompanied by any remarks which the superintendent may think proper to offer. Besides the above trials, it is directed that the engines of all ships in commission for service at sea are to be worked at full power twice during each year by their own complement. The first full-power trial is to be made when the ship is commissioned ready for sea, after the dock-yard trials to test the machinery have been made, and it is to be of six hours' duration. In reviewing the above and considering the subject, it may be ques tioned whether the system thus prescribed for testing the strength and power of motive machinery and the speed of a vessel be not seriously objectionable; also, whether any practical purpose is thereby served. It has been seen that the coal used on the trials is of the very best quality; that the firemen employed are the best trained and most expert in the service; that the machinery is placed in the most complete order, and that under these conditions the engines and boilers are forced to the utmost extent of their capabilities, the time engaged in running the measured mile being only a few minutes. Now, it may reasonably be asked whether the excessive strain to which the machinery is subjected while undergoing this severe test does not leave weakness in some hidden parts, and is not the cause of defects subsequently exposed. Furthermore, as the engines can never under any possible conditions be worked at sea for any extended time up to the measured-mile speed, it may be asked what practical purpose is served by it, except that of recording a speed never afterward attainable under any other conditions. It may, moreover, be instructive as regards the speed of the armored ships, to refer to the proceedings of the court-martial held at Devonport in September, 1875, to inquire into the loss of Her Majesty's ship Vanguard by collision with a sister ship, the Iron Duke, off the coast of Ireland, September 1 of that year. The commanding officer of the Iron Duke, Captain Hickley, being Sworn and examined, testified as follows to questions: 768. It is stated in the steam-register that at 12.30 Iron Duke was going fifty-four revolutions; what speed would that produce?-Answer. Eight knots. 769. And at 12.40, sixty revolutions; what speed would that produce?-Answer. Eight and one-half knots, or under. And I may refer to the log of the 23d of August, that on leaving Loch Swilly under full speed, to pick the squadron up, she was going eight and one-half knots at sixty revolutions. 770. What was the state of the weather on that occasion ?-Answer. Very fine. $16. How many revolutions do Iron Duke's engines go at their utmost speed-all boilers?-Answer. The only opportunity I had of judging was on the 23d of August, and on a short trial we had to test the engines; sixty-three revolutions was the utmost we could get, with most indifferent stokers. # J. D. CHARTER, engineer in Her Majesty's ship Iron Duke, being sworn and examined, testified as follows to questions: 1076. What is the pitch of your screws ?-Answer. Twenty-one feet. 1077. What is the slip percentage in calm weather?-Answer. The slip varies according to the number of revolutions we are making. S. Ex. 27-9 1078. Fixing your revolutions at sixty, what is the slip-Auswer. About 15 per -cent. 1079. Going at sixty revolutions with a screw of 21 feet pitch, what speed would that give?-Answer. About ten and one-half knots. Taking the pitch of the screws and the revolutions as above given, it appears from the testimony of the captain of the ship that about 8.92 knots was the maximum speed that could be obtained by the Iron Duke, while from the testimony of Engineer Charter it would appear that a speed of about 11.02 knots was possible when working the engines to the utmost. Now, by referring to the tables of armored ships in this report it will be seen that the speed of the Iron Duke on the measured mile was 13.6 knots. This great discrepancy could not be owing even in a small de gree to foulness of the iron bottom, (the bottom is not sheathed with wood,) for, if so, the slip of the screw would have very largely exceeded 15 per cent. It appears also, from the testimony given before the same court by the commanding officer of Her Majesty's ship Vanguard, Captain Da kins, that the maximum speed of that ship was nine knots, or there. abouts. It may probably not be fair to make an abatement for the speed of all British armored ships in accordance with those sworn to for the Iron Duke and the Vanguard; but from the testimony in these two cases, we may reasonably conclude that a wide margin exists between the speeds of the ships at the measured-mile trials, and the maximum speed that can be obtained when cruising at sea. The real speed of a ship is that recorded under full power at sea in ordinary weather during 12 to 24 hours consecutively, and of this we have but little from any ships of the British navy.* In considering this subject it may be well to remember that the "indifferent stokers" referred to as being on board the Iron Duke, although inferior to those employed on the measured-mile trials, are far superior to the firemen that have been employed in our naval vessels within seven or eight years. * Have no record of the Sultan-Bellerophon relative-speed trial of 24 hours in 1873. |