set of engines and line of shafting, so that the propelling machinery of
each ship is duplicated throughout. The speeds attained indicate a high
efficiency with the twin screws. In all ships, but more especially in high
speed ships, success depends largely upon the provision of propellers
suited for the work they have to perform, and where a high propulsive
efficiency has been secured, there is no doubt the screws are working with
a high efficiency. The principal purpose of this paper is to record the
particulars of the propellers, and the results of the trials of several of
these high speed twin screw ships. The table gives the leading particulars
of several classes of ships, the particulars of the screws, and the results
obtained on the measured mile trials from a ship of each class, except C.
The vessels whose trials are inserted in the table have not been selected
as showing the highest speeds for the several classes. Excepting C, they
are the ships which have been run on the measured mile at or near the
designed load water line. On light draught trials, speeds have been
attained from half a knot to a knot higher than those here recorded. No
ship of the class C has yet been officially tried on the measured mile, but
as several are in a forward state, perhaps the actual data from one of them
may shortly be obtained. All these measured mile trials were made under the
usual Admiralty conditions, that is to say, the ships' bottoms and the
screws were clean, and the force of the wind and state of the sea were not
such as to make the trials useless for purposes of comparison. On such
trials the i.h.p. is obtained from diagrams taken while the ship is on the
mile, and the revolutions are recorded by ruechanical counters for the time
occupied in running the mile. Not less than four runs are made during a
trial extending over several hours. The i.h.p. in the table is not
necessarily the maximum during the trial, for the average while on the mile
is sometimes a little below the average for the whole of the trial. The
revolutions are the mean for the two sets of engines, and the i.h.p. is the
sum of the powers of the two sets. The pitch of the screw is measured. The