The crew on board Team Sun Hung Kai/Scallywag have released details of how John Fisher became lost overboard.
The team has been forced to give up on the search for the 47-year-old in the southern ocean, approximately 1400 nautical miles west of Cape Horn due to deteriorating conditions.
The British sailor was hit by the boom during an accidental crash gybe and was not wearing his safety tether.
"This is the worst situation you can imagine happening to your team," said SHK/Scallywag Team Manager Tim Newton, who has spoken with skipper David Witt and navigator Libby Greenhalgh about what happened on Monday (Tuesday NZ time).
"We are absolutely heart-broken for John's family and friends. I know for David, he has lost his best friend. It's devastating."
Newton says he asked the crew to put together a timeline of events to ensure accurate reporting on the incident, and it is understood that Fisher was unconscious from the blow before he hit the water.
The timeline says two buoys were thrown off the boat to mark his position, but it took some time to get the boat under control and back to the mark due to the weather conditions.
A search and rescue operation was carried out for several hours, but there was no sign of John, the horseshoe buoy, or the JON buoy, the team said.
Newton says the team is distraught but has a clear focus on getting the crew and boat back to shore.
"This situation isn't over yet for our team," Newton said.
"The conditions are extremely challenging, with strong winds and a forecast for a building sea state over the next couple of days. Our sole focus, with the assistance of Race Control in Alicante, is to get the team into port safely.
"Once we have achieved that, we have time to de-brief more fully and ensure that any lessons that can be learned from what happened to John are incorporated by the rest of the fleet going forward.
"That would be a tremendous legacy for John, who spent so much of his time passing the learning's from his lifetime of experience at sea onto the younger sailors on our team."