Berthing Very Large Container Vessels

Use of tugs for berthing and unberthing very large container vessels is a high precision job,requiring deep appreciation of all the factors that influence these vessels and complete synergy between all members of the Bridge Team. Every manoeuvre is unique, even ones that are at the same berth with same vessel or class of vessels and same meteorological conditions.

Available tug power and ultra dead-slow speed of approach contribute significantly to berthing or unberthing these vessels successfully while ensuring the risk of damage to vessel and/or pier or cranes is reduced to zero. Setting up the ECDIS correctly, interpreting doppler log data intelligently, recognising when the data is unreliable, UKC, turning room in the basin and - if the turn is to be executed in a river with current - downstream drift while turning, the port's past experience and simulated turning times for such manoeuvres for different vessel types and sizes, are just a few amongst a plethora of factors that need to be kept in mind when assessing risks. Every port has data on time taken to turn vessels of different types and sizes through,say, 180 degrees under different conditions.This is extremely valuable information, and if made available to the shipmaster, contributes hugely to the safety of manoeuvre. Combining all this with the watchful alertness of the Bridge Team raises the safety bar.

Ideally, a speed of landing on the fenders at berth of < 0.1 kts is preferred, but occasionally this can be higher.Under worse case scenarios, sufficient kinetic energy is transferred to cause great harm to assets.

Inadequate tug power and insufficient number of tugs can often be a hidden culprit in this error chain.

I received excellent guidance from a friendly senior pilot once, which I have summarised below. The rule of thumb used in some key regions (and ports) around the world - as per this information - is as below :

Europoort (Holland)  :

Total tug power (in tonnes) =  Vessel displacement / 3000

Japan :

Total tug horsepower = Vessel displacement / 10

Total tug power (in tonnes) =  { (Vessel displacement x 60) / 100000 } + 40 

Sweden  :

Tug horsepower per 1000 m2 wind area in tons =  v2 / 18  (where 'v' is wind speed in m/s)

Tug power (in tonnes) = {wind area x v2} / (1000 x 18).

It was mentioned that the Swedish formulae takes the freeboard into account in the calculation and is the easiest to use. It was pointed out that there can be a large variance from port to port. (Author's opinion :  above guidance is a good tool in the Master's armoury when arriving at a decision regarding total tug power to order).

This beneficial information was further supplemented with a handy 'conversion'  factor from tug engine power to bollard pull, something that is not readily available to the shipmaster and I hope it will help us all : 

Bollard pull of tug (in tonnes) =  (Engine power in kW / 74 kW) x constant. The constant given for each type of tug is :

Propeller type / constant :

Ordinary propeller / 1.3

Nozzle / 1.6

Voith Schneider / 1.0

The shipmaster must, of course, bear in mind that 100% tug power may not be available,being influenced by various factors itself,not least amongst them the tug's own speed and that of the vessel.

Source  :  text in italics made available by a senior marine pilot in Port Klang,Malaysia.