pitch
1.205, fraction 0.378; relative resistance 3.5, pitch 1.279, fraction
0.355; relative resistance 3, pitch 1.357, fraction 0.334; relative
resistance 2.5, pitch 1.450, fraction 0.313; relative resistance 2, pitch
1.560, fraction 0.294; relative resistance 1.5, pitch 1.682, fraction
0.275. The relative resistance of 4 is that which is usual in an auxiliary
line of battle ship, 3.5 in an auxiliary frigate, 3 in a high speed line of
battle ship, 2.5 in a high speed frigate, 2 in a high speed corvette, and
1.5 in a high speed despatch boat.

607. _Q._--What are the corresponding proportions of screws of four blades?

_A._--The ratios of the pitches to the diameter being for each of the
relative resistances enumerated above, 1.342, 1.425, 1.513, 1.607, 1.705,
1.810, 1.933, 2.080, and 2.243, the respective fractions of pitch or
fractions of a whole convolution will be 0.455, 0.428, 0.402, 0.378, 0.355,
0.334, 0.313, 0.294, and 0.275.

608. _Q._--And what are the corresponding proportions proper for screws of
six blades?

_A._--Beginning with the relative resistance of 5.5 as before, the proper
ratio of pitch to diameter for that and each of the successive resistances
in the case of screws with six blades, will be 1.677, 1.771, 1.891, 1.2009,
2.131, 2.262, 2.416, 2.600, 2.804; and the respective fractions of pitch
will be 0.794, 0.749, 0.703, 0.661, 0.621, 0.585, 0.548, 0.515, and 0.481.
These are the proportions which will give a maximum performance in every
case.[1]

[1] In my Treatise on the Screw Propeller I have gone into these various
questions more fully than would consort with the limits of this
publication.

SCREW VESSELS WITH FULL AND AUXILIARY POWER.

609. _Q._--Do you consider that the screw propeller is best adapted for
vessels of full power, or for vessels with auxiliary power?

_A._--It is, in my opinion, best adapted for vessels with auxiliary power,
and it is a worse propeller than paddle wheels for vessels which have
habitually to encounter strong head winds. Screw vessels are but ill
calculated--at least as constructed heretofore--to encounter head winds,
and the legitimate sphere of the screw is in propelling vessels with
auxiliary power.

610. _Q._--Does the screw act well in conjunction with sails?

_A._--I cannot say it acts better than paddles, except in so far as it is
less in the way and is less affected by the listing or heeling over of the
ship. A small steam power, however,