ll made on
paddle vessels. Have similar coefficients of performance been obtained in
the case of screw vessels?

_A._--The coefficients of a greater number of screw vessels have been
obtained and recorded, but it would occupy too much time to enumerate them
here. The coefficient of performance of the Fairy is 464.8; of the Rattler
676.8; and of the Frankfort 792.3. This coefficient, however, refers to
nautical and not to statute miles. If reduced to statute miles for the
purpose of comparison with the previous experiments, the coefficients will
respectively become 703, 1033, and 1212; which indicate that the
performance of screw vessels is equal to the performance of paddle vessels,
but some of the superiority of the result may be imputed to the superior
size of the screw vessels.

INFLUENCE OF THE SIZE OF VESSELS UPON THEIR SPEED.

549. _Q._--Will large vessels attain a greater speed than small, supposing
each to be furnished with the same proportionate power?

_A._--It is well known that large vessels furnished with the same
proportionate power, will attain a greater speed than small vessels, as
appears from the rule usual in yacht races of allowing a certain part of
the distance to be run to vessels which are of inferior size. The velocity
attained by a large vessel will be greater than the velocity attained by a
small vessel of the same mould and the same proportionate power, in the
proportion of the square roots of the linear dimensions of the vessels. A
vessel therefore with four times the sectional area and four times the
power of a smaller symmetrical vessel, and consequently of twice the
length, will have its speed increased in the proportion of the square root
of 1 to the square root of 2, or 1.4 times.

550. _Q._--Will you further illustrate this doctrine by an example?

_A._--The screw steamer Fairy, if enlarged to three times the size while
retaining the same form, would have twenty-seven times the capacity, nine
times the sectional area, and nine times the power. The length of such a
vessel would be 434 feet; her breadth 63 feet 4-1/2 inches; her draught of
water 16-1/2 feet; her area of immersed section 729 square feet; and her
nominal power 1080 horses. Now as the lengths of the Fairy and of the new
vessel are in the proportion of 1 to 3, the speeds will be in the
proportion of the square root of 1 to the square root of 3; or, in other
words, the speed of the large vessel will be 1.73 times grea