A Sydney sailor who survived months at sea eating raw fish and drinking rainwater with his dog is "stable and very well", his doctor has said.

Tim Shaddock, from Sydney, and his dog Bella were found stranded in the Pacific Ocean after their boat was damaged in a storm, weeks into their trip from Mexico to French Polynesia.

Shaddock's doctor told 9News the man had "normal vital signs".

Professor Mike Tipton, an ocean survival expert, says luck was only a part of the pair's incredible story.

"It's a combination of luck and skill," he told Weekend Today.

"And also knowing for example, as Tim did, that during the heat of the day you need to protect yourself because the last thing you want when you're in danger of becoming dehydrated is to be sweating."

Tipton said the key element for survival was being able to secure a fresh supply of water - and for Shaddock this came down to climate and location.

"These voyages of any great length tend to occur in the Pacific," he said.

"If you look back through history, they tend to occur in warm environments because if it was a cold environment you don't survive long enough."

Nonetheless, he described Shaddock's rescue as a "needle in a haystack" situation.

"People need to appreciate how small the boat is and how vast the Pacific is. The chances of someone being found are pretty slim," he said.

How did the ill-fated journey unfold?

Shaddock and Bella departed La Paz in Mexico three months ago, but just weeks into the voyage they were hit by a storm, which crippled their vessel.

The pair got the bare essentials by drinking rainwater and eating raw fish for months.

They spent their days waiting, and hoping for rescue.

Salvation came about two months later when a helicopter accompanying a tuna trawler spotted the drifting boat.

When Shaddock was found, he appeared to be healthy and in good spirits - all things considered.

"I have been through a very difficult ordeal at sea," he told 9News.

"I'm just needing rest and good food because I have been alone at sea a long time.

"Otherwise I'm in very good health."

The 51-year-old is still on his way back to dry land, where he will be met with further medical assistance.

His companion Bella is also looking safe and well.

Tipton said it would have been an isolating few months and likened Shaddock's story to a real-life Cast Away, referring to the 2000 movie tarring Tom Hanks.

He said having Bella onboard would have helped a "tremendous amount".

"I think that may have well made the difference," Tipton said. 

"You're living very much from day-to-day and you have to have a very positive mental attitude in order to get through this kind of ordeal and not give up.

"But also, having a plan, rationing yourself in terms of water and food, is really the secret to long survival voyages.

"Just imagine how dark and lonely it would feel out there at night time."

Tipton added Shaddock will need to slowly wean himself back onto a normal diet.

"It has to be a slow return to normal and he will probably need to be kept an eye on for several months."