Principles of Good Mooring
Until the advent of bulk transport of goods and raw materials by sea, the basic requirements of a mooring system were to prevent the vessel from drifting away from a berth or from colliding with adjacent moored vessels. The system had also to allow for assisting in heaving the ship up to the berth and in leaving the berth. Present situations often require the ship to be accurately held in place in relation to berth-mounted ship loading or discharging equipment which itself may be very limited in movement, e.g. container cranes and articulated booms.
The principle to be followed, regardless of the size of the vessel, is to restrain movement to within acceptable limits by means of an adequate number of mooring lines, which can be readily handled by the operating personnel, compatible with the conditions of wind, tide, weather and other effects likely to be experienced during the relevant period of vessel stay at the berth.
The berth designer should provide facilities to permit all vessels for which the berth was designed to remain safely moored alongside and mooring points should give a satisfactory spread of moorings and be disposed as nearly as possible symmetrical to the mid-point of the berth. It should be noted that vessels such as LNG/LPG tankers and coastal tankers do not necessarily have their manifolds amidships and will not therefore always lie centrally on the berth. The height of mooring points should be such that vertical angles of mooring lines will be as small as practicable and preferably not greater than 25°.
The optimum pattern of mooring lines for normal alongside berthing is likely to consist of a basic web of breast, head and stern lines extending from or near the extremities of the vessel, together with spring lines from approximately the quarter points of the vessel.
The physical nature and layout of the berth or terminal will affect the manner in which the mooring objectives are achieved and the relative position of shore-mounted mooring equipment may result in a pattern of lines that gives an inferior restraint capability. In such circumstances the berth designer should inform the operator of the berth what assistance may be necessary to achieve adequate restraint consistent with the forces acting on the moored ship and the demand of the discharge or loading operations.
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