Common Mooring Methods Used For Ships

Each ship/vessel has been designed with mooring arrangements such that ropes and wires of recommended strength can help it moor safely alongside a berth, floating platform, buoy or a jetty. Fundamentally a ship/vessel has to be positioned alongside a jetty or a berth, between mooring buoys, to a mooring buoy, to another ship or barge and then made fast using her own anchors, mooring lines or shore lines.

Some very common methods of mooring are Mediterranean mooring, Baltic mooring, Running mooring, Standing mooring, Spider mooring buoys , Single point or single buoy mooring, Conventional or multi buoy mooring, Ship to Ship Mooring

While Moored alongside a fixed or floating jetty or a sea berth there are various forces action on the vessel such as wind, current, tide, wave action, swell, surging induced due to passing ships and trim of the vessel. The spring, breast and head lines prevent vessel’s movement against the action of these forces. The directional effect of these need not be unidirectional. It can be multi-directional or at various angles to the vessel. The resultant direction of these forces often changes with change in direction of onshore/offshore winds or tidal streams, currents upriver and down streams. Thus a combination of breast ropes, head ropes and spring ropes is the best method to counter these forces and keep the vessel safely alongside.

Often mixed moorings are observed as some terminal based on local conditions and experiences require vessels to use more lines than they are designed for . Thus the method in which wires in conjunction with soft ropes with different SWL and construction are used as well is termed as Mixed mooring. The simplified resultant of these forces would tend to move a vessel in transverse or longitudinal direction with respect to the jetty. Thus spring lines prevent the longitudinal motion and the breast lines check the transverse motion.

It is always preferred to avoid mixed moorings due to variable loads and elasticity of various kind of ropes and wires which lead to different strain or weight on the lines. This can result in excessive loads on some lines than others and eventually part them putting the vessel in danger. However,  for safety reasons or in a desperate situation shipmasters or pilots may have to resort to mixed moorings.

Vessels sometimes also use the seaward anchor in conjunction with mooring lines to haul the vessel out of jetty while casting off or while making fast the vessel alongside use the seaward anchor to assist the control of the rate of lateral movement towards the berth. This manoeuvre can be carried out with or without the assistance of tugs.

Ship to Ship transfer operation involves mooring alongside of two different or same sized ships for cargo transfer. During this operation either one of the ships is at anchor or both are underway. The mooring arrangement depends on the size of the ships. A vessel either at anchor or stopped and maintaining a constant heading is approached by the manoeuvring ship at an angle of approach as smaller as practicable. The region of approach is usually abaft the beam of the constant heading ship. During the approach as the manoeuvring ship comes closer, it steers a course parallel to the heading or course of the other ship and reduces the horizontal distance between ships to less than 100 metres. Once this state is achieved the manoeuvring ship uses engine and rudder movements and reduces this distance further until the fenders touch eachother. The two ships thus then make parallel contact and the lines are passed respectively as per the mooring plan. As a common practice during the approach the wind and sea are preferred to be from ahead or at very small angles to the bow.