A large tanker is being assisted by a small tug made fast forward during a port approach. There have been incidents where such tugs have been pulled under the tanker's bow and capsized. What is the underlying cause of this danger, and how can it be prevented?

A. This only occurs in shallow water and never in deep water

B. Hydrodynamic "interaction" between the two vessels — as the large vessel moves through the water, the pressure field around its hull can draw the smaller tug in towards (and potentially under) the larger vessel's bow, particularly at higher speeds; prevention includes keeping the large vessel's speed low during tug operations and maintaining appropriate positioning/communication between the vessels

C. The tug's engine power is simply too weak compared to the tanker, with no relation to either vessel's movement through the water

D. The danger is caused only by the tug's towline being too short

A. The tidal height at the time of transit to confirm sufficient under-keel clearance

B. The yacht's fuel consumption for that leg

C. The colour of the seabed shown on the chart

D. Only the distance to the next waypoint

A. Assess the situation against the planned route and charted depths, take action to maintain safe water, and inform the Master if there is any doubt

B. Ignore it — ECDIS alarms are frequently false and can be left running

C. Switch the ECDIS to standby mode and navigate by GPS position alone

D. Acknowledge and silence the alarm immediately so it does not distract the helmsman