Due to the very low power-to-weight ratio found in large deadweight ships, their high inertial values and the very long reaction time to manoeuvring commands, difficulties often arise in achieving entry to the berthing area at an exactly pre-determined speed over the ground.

This paper describes a dynamically programmed optical aid to help the navigator achieve exactly the prescribed speed over the ground as he decelerates along his traverse or intended track when approaching his terminal or swinging area. The authors are consultants to AGA Navigation Aids Ltd who have developed this device.

Over the last decade or more, some very significant changes have occurred in the general requirements relating to the handling and manoeuvring of certain classes of modern vessel in the approach to their terminal berth – whether jetty, single-buoy mooring or even when coming to anchor. The economy of size in the bulk trades has probably had the most profound effect. This often reduces the power/weight ratio of the vessel itself to a very low order. In turn this has led to radical adjustments in techniques of ship handling in the final approach phases, due to the long response time between command instructions and reactions to these by the vessel itself. When considering the inertia of a vessel of 220000 tons deadweight or more – where the feasible deceleration or rate of change of speed is also of a low order – we can see the difficulties met with when endeavouring to enter the berthing area at an exactly required pre-determined speed over the ground (as opposed to speed through the water) often as low as one tenth of a knot or less.