Looking at the boat, the exhaust outlet is close to an open cabin vent, and the wind was blowing fumes back towards the boat from the quay wall behind. What does this explain?

A. The exhaust position makes no difference to where fumes end up

B. Exhaust fumes can be pushed back into a boat by wind direction, nearby walls, or other boats blocking normal airflow — even an exhaust that normally vents safely away from the boat can sometimes blow fumes back in given the wrong wind and mooring position

C. Fumes only ever travel away from a boat and could not possibly have come back inside

D. This explanation is irrelevant since CO poisoning is always caused by a faulty engine

A. Carbon monoxide (CO) poisoning from engine exhaust fumes — CO is invisible and has no smell, so headache, drowsiness, and feeling sick with no other obvious cause, especially with an engine running nearby, should always raise this possibility immediately

B. Seasickness, even though the boat is moored still in harbour and not moving

C. A normal reaction to being in a small cabin and not worth investigating

D. Simple tiredness from a long day — nothing further needs to be considered

A. Wait a few minutes to see if the headache passes on its own before doing anything

B. Turn off the engine immediately and get everyone out into fresh air on deck straight away — stopping the source and getting clean air to the casualties matters more than anything else in the first moments

C. Move the affected crew to a different part of the cabin, away from fresh air, to rest quietly

D. Open a small hatch slightly but keep the engine running, since it is needed for the battery charge