OCIMF_Mooring_Equipment_Guidelines_(Second_Edition)

If main mooring lines comprise of synl.bet.ic ropes, then traction winches speciaUy designed for
synthetic rope are recommended. These winches are' normally equipped with twin traction drums
with grooves and a storage reel mounted on, or below, deck.

For warping ends, which are ordinarily used for natural or synthetic fibre ropes but not for steel
wire ropes because of handling difficulties due to stiffness, ISO 6482 provides design criteria for
tbe recommended diameter and leng1h, nominal dimensions and the profile types.

7.4 WINCH DRIVES

Winch drums are driven through reduclion gears by a motor which may be powered by steam,

electricity or hydraulic pressure. HydrauLic motors may be powered by a ceTllral power pack (which

may ruso be used to power other motors such as tbose of cranes or cargo winches), or may be part

of a seJf-contaiJ\ed winch incorporating an electrically driven hydraulic pump i.n each winch. Anolher

version of a unitised hydraulic winch drive employs a torque convener for power transmission between

an electric moLor and tbe winch gearing.

The winch drive should ideally allow for continuolls variation in line speed, permitting heaving and

rendering at high speed when the load is small, and developing higb pull when the speed is low. The

pull at stalled heave shouId n.ot exceed 50% of the mooring line's MBL to prevent routine over-

stressing of the mooring Line.

The considerations guiding the seleclioo of drive systems at a ship's design stage wilT not be discussed

in detail. since many are beyond the scope of this guide: these include initial cost, maintenance

cost, energy cost. re.liabilily, company experience, climatic conditions, availability of steam and inter-

connection with other systems. There are also many variations within each category (especially within

hydraulic and electric systems) that may Significantly alter the performance, relicability and cost. Any

of these are accept.able aboard tankers if they are properly designed and executed.

The following short discussion, on each basic type places emphasi,s on the speed/pull characteristics;

7.4.1 Steam

Steam winches have been most popular on large tankers. They are simple, safe, robust aud have an

ideal speed/pull characteristic. A minor drawback of the typical twin cylinder double acting steam

engine is tbe non-uniform torque (varying by up to 500]0 for each 45070 of crankshaft rotation). This

is most noticeable at very low speeds.

Because of the change from steam main propul~ion systems to diesel systems, even on tbe largest

ships, hydraulic systems have gained in popularity.

7.4.2 Hydraulic Drives

The speed/pull characteristic \'aries with the type of motor:

• The speed of a low pressure vane mOlor can be infinitely varied up to t.he fated speed by a
  special throttle valve. High slack rope speeds can be obtained only by suirable drive modi-
  fications to provide a high speed range al reduced torque.


• A bigb pressure variable displacement hydraulic motor has an ideal ~peed/pulJ characteristic
  wilhin certain limits. To achieve a higb slack line speed, a speed cbange provision is required.


• A torque convert.er drive has a similar characteristic as a variable displacement high pressure
  motor and it also requires a second gear step to provide for a high slack une speed.

7.4.3 Electric Drives

Electric drives arc the least p{)pular types on tankers due to certain inherent disadvantages. All

electric equipment in the cargo tank region must be of the certified safe type. Electric controls are