Ilfracombe’s all-weather lifeboat was paged early on Monday after an upturned boat hull was spotted nine miles out at sea.
The lifeboat launched at 7am after Ilfracombe fisherman and fellow RNLI crew member Ben Bengey alerted the coastguard.
The hull was originally spotted nine miles off Baggy Point but was eventually found some five miles east of Lundy South Lighthouse, and 17 miles from Ilfracombe.
The 18-foot fibreglass hull was in very poor condition and there was no sign it had been taken to sea by any person.
The crew attempted to tow it back to dispose of it. Filled with water, it was too awkward, yet it was still buoyant enough not to sink.
Eventually, the decision was taken to leave it, as it could not be recovered but was not a danger to shipping.
Ilfracombe RNLI volunteer coxswain Carl Perrin said: “The fisherman who called the coastguard did the right thing in raising the alarm.
“We are always happy to be called out when people believe lives may be in danger, as our principal concern is to make sure people are safe. If anyone does see someone they believe may be in danger, they should dial 999 and ask for the coastguard.”