"The water all around me was bright red - and I knew I had to try and escape or I'd either bleed to death or drown.
"So I mustered all my strength and managed to get away.
"I hoped I would be safe on the roof, and I was so frightened when it was ripped off.
"I was frantically grabbing for anything that might keep me afloat and I clung onto a piece of blue tubing which was floating above the waves. "Eventually it drifted to a house and I managed to haul myself onto the roof and waited there until I was rescued.
"I'm just so lucky to be alive." Family friend Yvonne Smith, who has been constantly in touch with David and John since the tragedy, said: "We have arranged for a plastic surgeon to be on standby at a hospital in Merseyside and if all goes well, he should be back in the UK by Friday. John's recovery is going to be a long, long haul before he even gets to walk again.
"But we haven't lost hope. If he comes back here, there is the chance his leg won't need to be amputated."
John, a former pupil of Croxteth Community School, has lived in Thailand since he became a diving instructor almost three years ago. His father is a commercial diver for companies in Saudi Arabia and the Far East.
Council officer Yvonne, 47, said: "All his life he wanted to be like his dad so he trained as a diving instructor. He had just started a new job in Phi Phi."
David has already spent around £15,000 funding John's treatment, as his son did not have any insurance cover to pay for his medical costs.
Now the father is selling his car and has put a house he owns in North Wales on the market to pay for treatment.