Factors Affecting Berthing
Berthing of vessel requires very specialized skills. Pilot has to take in account of various forces, external & internal which are variable to varying degrees as well as the vessel’s controls available to him.
Various factors are taken into account and amongst those included following but not limited to;
Size: A large vessel will be sluggish to turn. Her stopping distance will be considerably large as well as time taken to pick up speed.
Displacement of vessel: Displacement means total weight of the vessel. It is the total volume occupied by underwater part of vessel multiplied by the density of water. Larger the displacement greater will be the force required to move or stop it.
Wind speeds and direction: Exposed part of vessel acts like a sail. Off shore wind with a speed of 10 knots creates strong adverse wind force which needs to be controlled by using more tugs or bow/stern thrusters. On shore wind though will assist in berthing but strong on shore wind may push the vessel hard to berth causing damage.
Current: Current affects the maneuverability of the vessel. In tidal port with currents, berths are designed in such a way that current will be flowing at 15 to 30 degree to the berth. Design berthing velocity for ship is normally 0.2 m/second.
Tugs: Ship berthing tugs are powerful tugs that can fasten a line to the ship to pull the ship away from the berth, or push with their bow against the side of the ship move the ship towards the berth. The tugs are rated by horsepower and usually range from 1200 HP to 3200 HP.
Fenders: Due to the momentum shipside or jetty may be damaged due to impact of Alison. Fenders are used to avoid the damage and designed to absorb the energy of the berthing impact at around 25 % deflection.