We are all used to see ships berthed alongside quay or docks. We very seldom stop to appreciate the efforts put in behind it. It looks like a very easy job done by ship’s staff.
In reality berthing of vessel or ship on a wharf is quite a specialized job involving the use of several equipment, lines etc. It is more like parking of a car in a tight parallel parking slot. Since vessel is required to carry out cargo work at berth, positioning of vessel should be such that shore side cargo handling equipments are aligned with vessels equipments. The access way (gangway) is placed safely on the jetty.
Since the job is quite critical and ship’s staff is not familiar with local meteorological and topography of port, services of an expert, popularly called pilot, is sought. In fact in most of the ports, this service is mandatory. The adjacent picture shows a ship being berthed at a port.
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.
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.
- In a typical modern port, the vessel will approach at an angle of about 20 degree to berth. Vessel will be maneuvered in such a way that her speed will be one or two knots and forward part is some 10 meters away so that lines can be passed.
- Forward tug will be used to hold the bow so that she doesn’t come in contact with jetty. Engine will be reversed to stop the vessel.
- Aft tug will push the vessel towards jetty. When approach speed is more than 0.2 m/second, tugs are used to retard the speed.
- With careful use of engines and rudder vessel will be positioned when she is still few meters away from jetty.
- Once in position, vessel will be brought along side by using tugs and mooring ropes. Modern tugs with azimuth propeller can virtually push or pull the vessel without changing her position.
Berthing can be done in many ways. The exact method depends on various factors, some of which are alluded above. However like a car driver each pilot has his own method of berthing. And someone very truly said, “it is more of art than science.”
Cornship Company, Japan