CAPSTANS.
531
Capstans. —Capstans belong to the same dass of appliances as winches,
the only difference being that their axes are vertical instead of horizontal.
This arrangement favours the working of them by hand when necessary.
Accordingly the capstan head should be designed at a convenient height and
apertures for poles arranged in it, so that, in case of any breakdown in the
usual motive power, the machinery may be actuated by hand. A pawl and
ratchet gear along the lower circum-
ference will prevent backslip.
Capstans of from 3 to 12 tons
power are generally found sufficient
for dock work. Excessive power would
only result in the fracture of cables.
One capstan, at least, should be
located at each side of an entrance,
and if there be a long lock, two or
four others will certainly be advisable
at equal intervals. The position of a
capstan should be such that, if there
be a pair of gates in the vicinity, a
VERTICAL SECTION
Fig. 536. —Electric Capstan.
Fig. 535.
convenient lead may be obtained for opening or closing the gates in the
event of an accident to the gate machinery.
Capstans are obviously most, if not solely, adapted for working by means
of rotary engines. In the case of hydraulic power, an illustration of the
mechanism as devised by Lord Armstrong for a two-cylinder machine is
afforded in figs. 531 to 534. The method of admitting the pressure water to