Rob Atkinson, Padstow harbour master, issued a plea for people with speed boats fitted with a "kill cord" - a safety device to ensure a boat's engine is cut if the person in control goes overboard - to make sure it is operating correctly.
He told Sky News:
I can't talk about this incident - the Marine Accident Investigation Branch will investigate and determine exactly what happened.
But as a general, with these boats, there's a safety device fitted called a kill cord. Basically one end of the kill cord has to be plugged into the boat's controls, to make the engine operate.
That is joined by a cord, to the person in control of the boat.
If the person in control of the boat goes out of the boat for any reason, I am not sure how it happened in this case, that cord is pulled out of the boat's control, the engine stops instantly.
I can't comment on this, this speculation, but as a general plea to everyone out there who operates this sort of boat, please, please, please, when you have a boat fitted with a kill cord, make sure the kill cord is operating correctly and make sure it is attached to you because if you go out of the boat, it will stop the engine and it will prevent tragedies like this happening.
A father of four who was killed in a speedboat accident along with his eight-year-old daughter doted on his family", his brother has said.
Two people have died and another four people have been injured in a speedboat accident while on holiday in Cornwall.