Extensive full scale tests of a twin drum traction winch for 3 inch diameter wire rope have revealed that the drum grooving system is important for optimum performance of the winch and the wire. The back tension shall be sufficient, but not too large.
In a chain/wire system it is important that the pitch circle diameter of the connecting link is close to that of the wire during the passage over sheaves.
The term mooring is generally used whenever a craft is secured in a certain position by means of cables, although there is quite a difference between securing a barge in position by means of anchors and relative to an offshore. fixed structure.
In "single point mooring" the term is broadened, and the winches used for warping a pipelaying barge is frequently referred to as "mooring winches". This paper is related to machinery and equipment for all the above appliances.
Mooring cables are chain, fibre rope or steel wire rope, and the two first ones are in this paper only dealt with when they are connected to the steel wire rope in a mooring system.
The main problem concerning the wire handling on the machinery is wear of which there are-several types: Loss of material due to external and internal rubbing and corrosion, and permanent local deformation due to contact with other parts of the wire' the machinery, foreign objects, or bending in way of termination-sockets.
Bending over a small diameter sheave at high tens Lon can cause deformation for the whole wire rope length exposed to this treatment and lead to fatigue after a small number of such exposures. However, a heavy local deformation is considered worse since there is a large chance for rope breakage the next time this part of the wire is exposed to high load, especially during the passage over rollers or sheaves.
For the design of the mooring machinery the main objectives is to support the wire rope properly when it is passing over sheaves and drums at high tension, and to avoid undue hafing, slipping and bending at high tension. This may easily lead to heavy and expensive machinery and the designers' dilemma is a trade off between machinery price, size and weight on one side and rope performance of the other. Large sheave and drum diameters are expensive, but a certain gain is caused by reduced bearing losses.
Another design problem is internal structural strain.
Many tensioned rope parts acting together, for instance between drums or sheaves in a winch structure. or on a drum in several rope layers, can add up to substantial structural stresses.
The main mooring elements are fairleads, bollards, warping head/capstan and winches, Fig. 1.
