OF J»EOPELLEB

139

speed table. A 6-volt dry battery (3) provides the current necessary
to operate the distance recorder.

Fig. 10.—Chenukeeff Electnc Log,
The essential element is an impeller (5) fitted in a horizontal tube
at the end of a vertical rod which protrudes 10 to 15 inches outside the
bottom of the vessel. This vertical rod passes through a tube (8), which
is flanged and riveted to the shell plating at (7), a sluice valve (6) ensures
watertightness when the impeller rod is drawn inboard by means of its
handle at the top end.
The impeller is rotated by the flow of water passing the ship, the
pitch being such that it makes one revolution for every 1-35 feet of
distance run. The gearing and electrical connections are so arranged
that a contact is made at every 45th revolution of the impeller, that is,
on the completion of every 60*8 feet of distance run, The contact
energises the coil in the distance recorder and each impulse allows
the indicator to move 'round one division on the dial, each division
representing 60-8 feet of travel or one-hundredth of a nautical mile.
THE SPEED OP THE PROPELLER.
An approximation of the speed and distance sailed may be computed
from the revolutions of the ship's propeller, the uncertain factor in the
calculation being the "slip."