Marine Auxiliary Machinery Chapter 9 Lesson 4 Deck Machinery Mooring Equipment By Professor Zhao Zai Li 05.2006
MOORING EQUIPMENT(1) • Full load duties of warping capstans and mooring winches vary between 3-30 tonnes at 0.3 to 0.6 m/sec and twice full load speed is normally provided for recovering slack lines. • The size of wire rope used on mooring winch barrels is governed by the weight of wire manageable by the crew; this is currently accepted as 140 mm circumference maximum. • The basic problems associated with the use of wire ropes is that they are difficult to handle, do not float and when used in multi-1ayers, due to inadequate spooling, the top, tensioned layer cuts down into the underlying layers causing damage.
MOORING EQUIPMENT(2) • To counteract this latter problem a divided barrel can be used such that the wire may be stored on one portion and a single layer of wire transfered to the second portion when tensioned. • Low density, high breaking strength synthetic ropes (polypropylene, nylon, terylene etc.) offer certain advantages over wire, its main disadvantage being a tendency to fuse if scrubbed against itself or the barrel.
Winches (1) • Mooring winches provide the facility for tensioning the wire up to the stalling capacity of the winch, usually 1.5 times full load, thereafter the load is held by the prime mover brake or barrel brake when the power is shut off. • The winch cannot pay out wire unless the brake is overhauled or recover wire unless manually operated, thus wires may become slack.
Winches (2) • Automatic mooring winches provide the manual control previously described but in addition incorporate control features such that in the ‘automatic’ setting, the winch may be overhauled and wire is paid off the barrel at a pre-determined maximum tension; also wire is recovered at a lower tension should it tend to become slack. • Thus there is a certain range of tension, associated with each step of automatic control, when the wire is stationary. • It is not practical to reduce this range to the minimum possible as this results in hunting of the controls.
Winches (3) • It should be noted that the principal reason for incorporating automatic controls with the features described is to limit the render value of the winch and avoid broken wires; also to prevent mooring wires becoming slack. • Load sensing devices are used with automatic mooring winches, e.g. spring-loaded gearwheels and torsion bars are widely used with steam and electric winches; fluid pressure sensing, either steam or hydraulic oil pressure, is also used where appropriate.
Winches (4) • Mooring winches are usually controlled at the local position, i.e. the winch; for vessels of unusually large beam or where docking operations are a frequent occurrence e.g. in ships regularly traversingthe St. Lawrence Seaway, remote and shipside controllers are of great advantage. • As mooring techniques vary widely, the position and type of control must be engineered to suit the application
Winches (5) • It is considered, especially on vessels where mooting fines may be long and ship position critical, that the greatest asset to the operator is knowledge of the wire tensions existing during the mooring operation coupled with an indication of the amount of wire paid off the barrel. • It is quite feasible to record these at a central position and mooring lines would then only have to be adjusted periodically as indicated by the recording instruments.
Winches (6) • The majority of automatic mooring winches are spur geared to improve the backward efficiency of the gear train for rendering, the gearing and bearings being totally enclosed and lubricared from the oil sump. • On larger mooring winches were a barrel brake is fitted, it is now common practice to design the brake to withstand the breaking strength of the mooring wire. • Worm geared automatic mooring winches are uncommon as the multistart feature required to improve gear efficiency reduces the main advantage of the worm gear i.e. : the high gear ratio.