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8 MARINE REVIEW. Katahdin's Many Trials. EFFORTS MADE TO OBTAIN 17 KNOTS WITH THE FAMOUS RAM--PROPEL- LERS USED--SOME DATA FROM OFFICIAI, SOURCES. The Katahdin is the latest addition tothe United States navy, and although as regards speed she has failed to come up to the contract re- quirements, yet her efficiency as a ram is but slightly impaired. She needs no heavy armament, for she is her own weapon. Her destructive power is indicated by the following figures: At an ordinary cruising draft of 15 feet, and steaming at 16 knots speed, she will strike a blow of over w " we U. $.S. KATAHDIN ON OFFICIAL TRIAL--SPEED 11.16 KNOTS. 24,700 foot tons, a force capable of sinking any vessel that now floats. At 15 knots speed the blow would be about 21,700 foot tons and at 10 knots 9,660 foot tons. The Katahdin's greatest forte lies in her strength as a body and the excellence of her model for maneuvering and offensive and defensive powers. The stem or ram proper is formed by a 14-ton casting, and mas- sive girders and longitudinals converge to it from deck, keel and sides, well stiffened by breasthooks and intercostal frames and beams, so as to make all parts of the ship take the effect of the blow and insure no local weakness. The keel of the vessel is elliptical, and itis remarkable to see how rapidly she can turn and how quickly she answers her rudder, and this feature is absolutely necessary in a vessel intended for efficient harbor service. The bow and stern lines are remarkably full and hard and there is no deadwood or cutwater whatever. A sharp knuckle formed where the side and deck armor meet, about 8 inches under water, runs from the centre of the stem the whole length of the ship, and this will tend to rip out the side of a vessel struck. There are no important pro- jections above deck with the exception of the coning tower, which weighs 45 tons and is 18 inches thick, and the smoke pipe and ventilators, which at the base have 6-inch inclined armor for about 3 feet high. The deck is convex and completely armored, and there are two strakes of side armor below water from 3to6inches thick. Four 6-pound rapid fire guns are carried, two forward and two aft, in small barbettes as a protec- tion against light torpedo craft. _ The dimensions of the vessel are well known, but it may be well to state here that she is 251 feet long over all, 43 feet 5 inches extreme beam and 15 feet mean draft; displacement 2,183 tons. The engines are twin-screw horizontal triple expansion, with cylinders 25, 36 and 56 inches diameter by 36 inches stroke, designed for 4,800 horse power at 150 revolutions. There are two double-ended and one single-ended Scotch boilers, with 12,160 square feet of heating surface and 354 square feet of grate surface. On Dec. 10, 1894, the Katahdin made her first preliminary trial trip over a measured mile course off Southport, Me. The propeller wheels had a diamenter of 10 feet 6 inches, 15 feet 2 inches pitch and 30 square feet blade area. Her bottom was somewhat foul, and the engines not working satisfactory aspeed of but 14.4 knots was attained with 2,440 indicated horse power, the slip being 27.4 per cent. The vessel was then taken to the Charleston navy yard and docked. New wheels of 10 feet 10 inches diameter, 14 feet 4 inches pitch and 38.5 square feet blade area were fitted, and late in March, 1895, the second speed trial was made. A speed of 15.71 knots was attained, with 4,124 indicated horse power and the slip was reduced to about 22 percent. During April and May similar full power trials were made, the maximum speed obtained being 16.06 knots, with 5,749 indicated horse power and 27 per cent. slip, the power on this run being no less than 20 per cent, in ex- cess of contract requirement, and yet the speed was one knotless. On May 31 a progressive trial from 8 knots upwards was decided upon, but after reaching a speed of 13 knots the bed plate of the after or starboard engine broke, and the vessel returned to Bath under one engine. It was --$----. not until Ang. 17 that the progressive trial could be concluded, the max- imum indicated horse power developed being 5,059, which gave a speed of 15.86 knots and 25 per cent. slip. In the meantime a large cofferdam 40 feet long and 50 feet wide had been built by the Bath Iron Works, and when the Katahdin had completed her progressive trials with wheels No. 2, the stern was placed in the cofferdam and wheels of 12 feet diameter, 14 feet pitch and 386 square feet blade area were fitted. On Aug. 31 a progressive trial was made with these wheels and they showed considerable improvement over their predecessors. These screws had an inclined element aft of 15 inches in 56 inches, and were designed by the United States bureau of steam engineering from data received from the previous trials. The maximum speed was 16.07 knots, with 4,900 in- dicated horse power and a slip of but 16.7 per cent. The Bath Iron Works having worked out all the vessel's performances on a theoretical basis, then submitted them to the navy department, and the latter officials decided that all that could be done had already been done, and that the only course left was to run the vessel on her official trial and get all they could out of her. This the builders decided to do, as they had already spent $40,000 in experimenting with her. She was accordingly taken tothe Charleston navy yard and again docked, It was then discovered that one of the wheels had sprung somewhat, and the tips of the blades had been bent very badly by striking against the side of the ship. New wheels were therefore hurriedly cast, similar to the previous ones, but only 11 feet 10 inches diameter, and after having these fitted she left Boston and steamed to Long Island sound for her official speed trial. This trial took place in very unfavorable weather on Oct. 31, the result being that but 16.11 knots mean speed was attained with about 5,300 indicated horse power, or over 10 per cent. more than the contract specified. It is undoubtedly the model of the Katahdin that is faulty, but Mr, William A. Fairburn of the Bath Iron Works, who has made all the caculations and curves of the vessel's performances during her speed tests, is confident that the speed could be increased from one-half to three- fonrths of a knot per hour by moving the propellers much farther astern. A couple of struts and anew length of shafting would be neces- sary, but the total cost of the change would not exceed $5,000. The fact of having the propellers so far astern would certainly provea slight detriment to the efficiency of the ship for harbor service, but this could be overcome to a great extent by building propeller guards that would project so far from the side of the vessel as to completely protect the wheels. This is done on most torpedo craft, and it should be remem- bered that the propellers as now located on the Katahdin preject beyond the side of the ship and are unprotected. It is said that Chief Engineer Melville of the bureau of steam engineering has proposed to the secre- tary of the navy that the wheels be moved aft and if this proposition is approved it will be interesting to watch the result of this trial. The Katahdin has made over fifty runs over the measured mile during her preliminary speed trials. For low speed up to about 13 knots the model is admirably adapted, and at 13 knots the admiralty displacement co-efficient of performance is 260. This good performance at low and medium speed is undoubtedly due tothe small wetted surface of the vessel. At 15 knots the'performance co-efficient has dropped to 165, and U.S. S. KATAHDIN--FORCEK EXPENDED IN WAVE MAKING. at 16 knots itis but 135. All the propellers fitted have brought out about the same final results, and as slip. was decreased so were revolu- tions and toacertain extent indicated horse power, and as regards the prime object--speed--the first wheels fitted were almost as satisfactory as the last ones. It is also a well known fact that the change in the wheels made just before the vessel went out on her official trial was not by any means beneficial to her.