The man had entered the water, wearing a wetsuit, to try to free a rope fouling the 30ft boat’s propeller.

After some time the skipper got back into the boat, called Last Straw, but his wife and daughter were concerned he was suffering the effects of the cold.

Unable to handle the boat herself the woman called the coastguard for help at around 9.40am.

Staithes lifeboat and the Whitby all-weather lifeboat were launched with local doctor and crewman, Graham Croft, on the scene.

He treated the man for hypothermia and all of the family were transferred to the Whitby lifeboat.

While the George and Mary Webb took the family to a waiting ambulance in Whitby, Staithes lifeboat towed the motor cruiser into Whitby.

Colin Harrison, helmsman of Staithes lifeboat, said: “This was a good, quick rescue with great teamwork between crews.

“It’s a stark reminder of how cold the sea is, even in August.

“Even wearing a wetsuit didn’t stop the onset of hypothermia.

“We would advise people to call for help if their propeller is fouled and not to enter the water.”