CAPSTAN GEAR

Capstan gear is normally fitted forward and aft in ships. The forward gear may comprise a separate cable/warping head which can be used for warping or working the anchors and cables and two cable holders which are designed to work the cables only, or two cable/warping heads which can be used for warping or working the cables. Anchor gear is not now carried aft but an after capstan head is fitted for warping, replenishment-at-sea and storing duties. Capstan gears can be powered nowadays by two methods, electric or electric-hydraulic.

·         ELECTRIC OPERATED CAPSTAN GEAR

This type is in common use in ships, where it consists, generally, of Duplex capstan gear in which the functions of a cable holder and capstan are combined in each of a pair of heads as mentioned previously. It is powered by a three-speed electric motor through a slipping clutch, a primary worm reduction gear, and a secondary worm reduction gear driving the capstan heads through vertical shafts. The driving gear is mounted under the forecastle deck, underslung on a main baseplate bolted to the deckhead. Each capstan head comprises a warping barrel mounted on the same spindle as a cable holder. The warping barrel always revolves with the spindle and so is always ready to use for warping. Vertical movement is provided so that the warping barrel can engage the cable holder which can then be used to haul or veer the anchor. When veering cable the cable holder is disengaged and controlled by handbrake. Neither head can be worked by hand. In larger ships, where space is less of a problem, the motors and gearing are seated on the deck below the forecastle, the vertical shafts being carried up through the latter.

The capstan gear, in this instance, consists of port and starboard wing cable holders and a middle line warping and anchor capstan, driven by two reversible electric motors through a slipping clutch, a geared driving unit and dog clutches. The wing cable holders, a handed pair, can be driven through an arrangement of dog clutches in either direction together, or independently, or be disconnected from the vertical shafts to run freely under the control of hand operated handbrakes. The body of each holder, like the lower barrel of the duplex head, is made of cast steel Grade I and formed with snugs into which the links of the cable fit neatly. The cable holders are not keyed to their spindles and each can revolve freely on a gunmetal bush and can be connected or disconnected from its spindle by a dog clutch. The skirt, or bottom flange, of the barrel forms braking surface for a band type of control brake which controls the speed at which the cable can be run out when the cable holder is disconnected.

The middle line capstan, normally operated independently of the wing cable holders, will revolve only in one direction relative to the motor direction and may be connected to, or isolated from, the motor drive through a dog clutch or by insertion or removal of two driving pins which couple the vertical shaft to a worm wheel. In the isolated condition the capstan can be worked by hand with bars fitted into sockets in the barrel head. These bars are made of ash wood bound with steel shoes which fit into the barrel slots snugly. They are secured by pins passing through the crown plate and shoes. Pawls dropped into a ratchet track located at the base of the barrel prevent the head from running back. Portable whelps can be fitted to facilitate working the ML head as a warping barrel but the wing cable holders are designed only for working the anchor cable. The electric motors are controlled by a portable T-handle fitted in a deck socket.

·         Electric-Hydraulic Capstan Gear

There are two forms of this type of gear. In the first the hydraulic motor and gearing which drive the capstan are incorporated in the actual capstan head as shown in the sketch. By virtue of its compactness this type is usually fitted aft in more modern ships designed with a comprehensive hydraulic system serving several equipments including the after capstan. In the second type the hydraulic motor drive replaces the electric motor drive described for the electric type of capstan gear and is otherwise similar to the latter as regards the design of capstan/warping heads, gearing, etc. Generally speaking this type is replacing the electric drive type in more modern ships forward. In both cases the electric motor and pump which supplies pressure oil to the hydraulic motor, whether the latter is incorporated in the capstan head or not, are situated on the deck below the capstan gear together with the control gear. In each a hydraulic control box is sited adjacent to the capstan and it is possible to work the capstan by means of a hand pump if electric power fails or is not available.

Brake Gear

In most types of capstan gear the brake is unidirectional and its Ferodo lined brake strap (of forged steel) is controlled by a hand wheel which operates through bevel gears to rotate a screwed spindle working in a trunnion nut. The brake strap is in two parts, connected by a joint pin with its head fitted in a recess in the underside of the forked part of the strap. The strap assembly is pivot anchored by a brake bolt in the deck plate. The other end of the band carries the trunnion nut in which the screwed end of the brake spindle works to contract or expand the band.

Controls

In all cases the capstan heads are controlled from the weather deck by means of a portable handle which fits into a socket let into the deck. The handle incorporates a pointer to indicate the handle position relative to the control markings marked on the flange of the socket. In addition the electrically driven capstan includes an emergency stop button set in the deck near to the control handle to stop the capstan in emergency.