nished by
shutting off the steam or otherwise, you will then have a larger screw
relatively with the power of the engine than before?

_A._--Yes.

585. _Q._--Was any experiment made to ascertain the effect of this
modification?

_A._--There was; but the result was not found to be better than before. The
experiment was made by shutting off the steam from the engines of the
Rattler until the number of strokes was reduced to 17 in the minute. The
actual power was then 126.7 horses; thrust upon the shaft 2 tons, 2 cwt., 3
qrs., 14 lbs; horse power of shaft 88.4 horses; ratio of shaft to engine
power 1 to 1.4; slip of the screw 18.7 per cent. In this experiment the
power utilized was 71 per cent.

586. _Q._--Was any experiment made to determine the relative performances
in head winds?

_A._--The trial in which this relation was best determined lasted for seven
hours, and was made against a strong head wind and heavy head sea. The
speed of the Rattler by patent log was 4.2 knots; and at the conclusion of
the trial the Alecto had the advantage by about half a mile. Owing to an
accidental injury to the indicator, the power exerted by the engines of the
Rattler in this trial could not be ascertained; but judging from the power
exerted in other experiments with the same number of revolutions, it
appears probable that the power actually exerted by the Rattler was about
300 horses. The number of strokes per minute made by the engines of the
Rattler was 22, whereas in the Alecto the number of strokes per minute was
only 12; so that while the engines of the Alecto were reduced, by the
resistance occasioned by a strong head wind, to nearly half their usual
speed, the engines of the Rattler were only lessened about one twelfth of
their usual speed. The mean thrust upon the screw shaft during this
experiment, was 4 tons, 7 cwt., 0 qr., 16 lbs. The horse power of the shaft
was 125.9 horses, and the slip of the screw was 56 per cent. Taking the
power actually exerted by the Rattler at 300 horses, the power utilized in
this experiment is only 42 per cent.

587. _Q._--What are the dimensions of the screw in the Rattler?

_A._--Diameter 10 feet, length 1 foot 3 inches, pitch 11 feet. The
foregoing experiments show that with a larger screw a better average
performance would be obtained. The best result arrived at, was when the
vessel was somewhat assisted by the wind, which is equivalent to a
reduction of the resistance of the hull, o