582. Q.—­Will you recapitulate some of the main incidents of these trials?

A.—­I may first state some of the chief dimensions of the vessels.  The Rattler is 176 feet 6 inches long, 32 feet 8-1/2 inches broad, 888 tons burden, 200 horses power, and has an area of immersed midship section of 380 square feet at a draught of water of 11 feet 5-1/2 inches.  The Alecto is of the same dimensions in every respect, except that she is only of 800 tons burden, the difference in this particular being wholly owing to the Rattler having been drawn out about 15 feet at the stern, to leave abundant room for the application of the screw.  The Rattler was fitted with a dynamometer, which enabled the actual propelling thrust of the screw shaft to be measured; and the amount of this thrust, multiplied by the distance through which the vessel passed in a given time, would determine the amount of power actually utilized in propelling the ship.  Both vessels were fitted with indicators applied to the cylinders, so as to determine the amount of power exerted by the engines.

583. Q.—­How many trials of the vessels were made on this occasion?

A.—­Twelve trials in all; but I need not refer to those in which similar or identical results were only repeated.  The first trial was made under steam only, the weather was calm and the water smooth.  At 54 minutes past 4 in the morning both vessels left the Nore, and at 30-1/2 minutes past 2 the Rattler stopped her engines in Yarmouth Roads, where in 20-1/2 minutes afterward she was joined by the Alecto.  The mean speed achieved by the Rattler during this trial was 9.2 knots per hour; the mean speed of the Alecto was 8.8 knots per hour.  The slip of the screw was 10.2 per cent.  The actual power exerted by the engines, as shown by the indicator, was in the case of the Rattler 334.6 horses, and in the case of the Alecto 281.2 horses; being a difference of 53.4 horses in favor of the Rattler.  The forward thrust upon the screw shaft was 3 tons, 17 cwt., 3 qrs., and 14 lbs.  The horse power of the shaft—­or power actually utilized—­ascertained by multiplying the thrust in pounds by the space passed through by the vessel in feet per minute, and dividing by 33,000, was 247.8 horses power.  This makes the ratio of the shaft to the engine power as 1 to 1.3, or, in other words, it shows that the amount of engine power utilized in propulsion was 77 per cent.  In a subsequent trial made with the vessels running before the wind, but with no sails set and the masts struck, the speed realized by the Rattler was 10 knots per hour.  The slip of the screw was 11.2 per cent.  The actual power exerted by the engines of the Rattler was 368.8 horses.  The actual power exerted by the engines of the Alecto was 291.7 horses.  The thrust of the shaft was equal to a weight of 4 tons, 4 cwt., 1 qr., 1 lb.  The horse power of the shaft was 290.2 horses, and the ratio of the shaft to the engine power was 1 to 1.2.  Here, therefore, the amount of the engine power utilized was 84 per cent.