OCIMF_Mooring_Equipment_Guidelines_(Second_Edition)

7.6.2 Raled speed (also called nominal speed or design speed)

Tbe rated speed is the speed that can be maintained with the rated load applied to the mooring line.

The rated speed in combination with the rated pull determines tbe power re.quiremenl for the winch

drive, The recommended fated speed is higher for the smaller size winches because the smaIler sizes

are intended for smaller ships and these warp and moor more quickly than large Sl1ips.

7.6.3 Slack line speed (aLro called no-load speed or lighl-line speed)

This is the speed that can be achieved by t.he winch with negligible load 011 the line. High peed is

essential to pass a line quickly to a shore mooring point or to bring the line quickly back on board.

The listed value recognises that during this phase the Ijne is normally not on the first layer, even

on split-drum winches, and tbe actual line speed could be up to 5011,10 higher. The slack line speeds

achievable are different for di.ffcrc(lt t~'Pes of drives and tllis must also be considered when specifying

perfonnance and drive type for new equipment. For example, a low pressure two· speed vant' motor

can achieve only twice the rated speed.

7.6.4 Stall heaving capacity (also caJ/ed stalling load)

This is the line pull the winch will exert \vhen the control is in heave and the line is held stationary.

A high stall heave capacity is desirable to winch a ship unto the pier against rugh environment.al

loads. On the other hand, the stall pull should not be so high that there is any danger of line

breakage, and should never exceed 50% of the mooring lines MBL. Achievable stall pull depends

on the drive type and control. As a rule of thumb the following ratios of stall pull to rated pull

roay be assumed:

Steam-driven 1.50

Hydraulic 1.0S

Elemi<; 1.25

7.6.5 Drum capacilY

The drum should be capable of stowing the total line length. Table 7.1 lists the drum capacities as

specified in ISO Standard 3730. Two capacities. 'normal' and high' are indicated. Winches witb

undivided drums could be more suitable [or the 'norma!.' capacity since this would reduce the number

of layers required. Nevertheless, many operators prefer longer hawsers and 365 metres would be a

representative length. ISO Standard 3730 also specifics that for undivided drums lhe tot.al number

of la.yers shall not exceed five for normal capacity drums and eight for high-capacity drums when

the total hawser length is stowed on the drum. For split drums, the number of layers 00 the storage

secrion may be higher. The ISO standard notes the possibility of line damage if large loads are applied

while more than four layers of rope are reeled on the drum. Presumably this applies to wire rope,

since the st.andard also warns of a short rope life if synthetic rope under tension is wound in more

than ODe lay~r.

On split-drum winches, it should be possible to store the lotal leogth of the mooring line on the

stowage part of the drum. This would facilitate the rapid payout of a line during mooring without

the need to transfer the line through the dividing flange slot. An allowance for 1.5 extra turns

should be made when determining the flange diameter of 'normal' capacity drums. I·or high' capacity

drums, no allowance need be made if wound with the layers superimposed directly upon each otber

(i.e. without a half-rope diameter offset between adjacent layers). On split drums. the tension section

should be wide enough for 10 turns of line.

7.7 STRENGTH REQUIREMENTS

The strength of tbe mooring winch st ructure should be based on the breaking strength of the Iioe

and the criteria given i.n Section 4. Tbe winch should therefore be clearly marked with the range of

rope strengths for which it is designed.