He will be in pitch darkness, perched on boxes of food, with three feet of water at his feet as the yacht pitches in heavy seas. Above the water level in the compartment, which measures nine feet by 10, will be an air pocket of about four feet to the ceiling, once the floor of the lower cabin on the now overturned boat.
"So much depends on whether he is getting air coming in through the door," said a member of Mr Bullimore's back-up team in Bristol yesterday. "And that depends on the height of the flooding, because everything is moving all the time."
Mr Bullimore's plight reopened the debate on whether it is best to remain on an upturned yacht or climb aboard a liferaft, like Thierry Dubois, the French competitor who capsized in the same storm.
Sir Robin Knox-Johnston, who sailed round the world in the 32ft Suhaili, said: "The wind-chill factor is horrendous, so if he goes on the top of the hull he would freeze even if he wasn't swept off by a wave. Down there he is out of the wind and may even be able to get dry. His food is down there with him, including his emergency rations, which would include water. As long as he has air and is not too cold, he could last a long time ... He is a tough little bugger but must now just wait another long 36 hours. We are all doing the same with everything crossed."
The inquiry into the 1979 Fastnet race, when 24 yachts were abandoned, found seven people died after boarding liferafts. Most of theyachts were recovered, suggesting it may have been safer to stay on board. James Stevens, national coach of the Royal Yachting Association, said: "There is a great temptation to get out when the boat is rolling, with things crashing around your head. But you are usually safer in the boat if it's still afloat. A yacht is a better liferaft than an inflatable."
In the yacht, however, there is a greater risk from lack of air or being trapped by changing water levels or moving debris.