What followed was a nightmare. Their wooden boat, on an island-hopping tour between Lombok and Flores, sank into the rough waters off Sangeang Island and the 20 foreigners and five Indonesian crew on board spent the next two days struggling to survive.

Most did, but more than a week later, two Spanish men are still missing and authorities have given up the search. Only good luck and determination saved many of the others.

The story is a lesson, say Ms Wilkinson and Mr Lawton, speaking to Fairfax Media from their Golden Bay home in New Zealand, in how shockingly inadequate safety is in a part of Indonesia that is hosting a rapidly growing number of tourists.

Their four day boat tour, which they bought from a seemingly reputable travel agent in the main street of Senggigi, was"dirt cheap" — about $NZ175 each ($AU160). But as it turned out, the wooden boat they travelled on had no satellite phone, no GPS or navigational equipment, no depth sounder. When it ultimately sank, there were no flares, the life jackets were shut in a cupboard in a hold that was rapidly filling with water, and the aluminium dinghy that acted as a lifeboat had no oars, no motor and room for just six people.

"You get what you pay for," Ms Wilkinson says ruefully now. "As soon as we'd bought the ticket, I said to Tony I think we've picked the wrong boat."

With Lombok an increasingly popular destination for Australians, and the island's ambition to grow a tourist industry to rival Bali's, their warning is timely.

It had all started so well. The boat, named the Versace, set off on Thursday August 14 from Lombok, heading east, with a mix of backpackers and middle-aged tourists, mostly from Europe, aboard.

That evening, a "beautiful, balmy night," Ms Wilkinson was sitting on the bow watching the water beneath as the captain, without charts or a depth sounder, was trying to pick his way in the dark through a series of shallow reefs. Then he hit one. Hard.

"We came to a dead stop. We were there for a couple of hours until the tide was high enough to be pushed off," Ms Wilkinson says.

"The guide was saying, "No problem, no problem, soft coral."

At first it seemed he was right, but Wilkinson and Lawton, who have a yacht, took the precaution of liberating two life vests from the hold and taking them to their cabins.

The next day, Friday, the trip lived up to the brochure. They landed at Mojo island and trekked up to a waterfall, then stopped for the "stunning snorkelling" and a salt lake visit at neighbouring Setonde. Then they set off for Komodo.

At about 1.30am on Saturday, in heavy seas off Sangeang, the panic began.

"The engine stopped because the hull was flooded … The weakened hull must have given, so now the boat had a hole, no bilge pump, and a hull full of water. It 90 per cent sank within half an hour."

After the guides had roused the passengers, Mr Lawton, bravely went into the flooding hull to retrieve the life jackets.

"The crew were hopeless. They accepted their fate and that was that," Ms Wilkinson says.

"The tourists were the ones getting the buckets and bailing. But the water was pouring in. It was obvious it was a losing battle."

Around that time, another boat came within perhaps a kilometre, but without flares they had no way of attracting it.

"Our Indonesian guide got a broomstick with a rag on the end and some kero, and had a live flame he was waving around. It was pretty frightening because by that stage there was fuel all through the water."

The tourists got on the lifeboat — six in the boat itself, the other 19 in the water hanging on. But then they decided to wait with the wooden boat which was still only partially submerged. For 20 hours they stayed there, sunburned, their eyes stinging, until on Saturday afternoon, it became unsafe.

"We were slowly sinking and it was getting dangerous. Waves were washing us off the roof, we were climbing back on, being washed off again," Ms Wilkinson says.

They abandoned ship at around midday on Saturday, with most going to the dinghy. But with Sangeang Island, an active volcano, in sight, five people, including Ms Wilkinson, began to swim for it with a young Dutch woman. Mr Lawton stayed with the dinghy trying to get the other 20 to kick or push it towards the island.

Ms Wilkinson swam for six-and-a-half hours, arriving at the island at sundown. Mr Walker, who realised attempts to power the dinghy were doomed, left a little later and arrived after dark and 10km further up the beach.

The next morning, Ms Wilkinson and a Dutch woman, Els, prepared to try to find help: they collected their urine in plastic bottles, found thongs, made sun visors and filled more water bottles at a sinkhole in a gully. Then a five-star dive boat, the Mermaid Liveaboard came by, spotted their life jackets on the beach and picked them up.

Mr Lawton, meanwhile, had been rescued by local fishermen.

Thirty hours after the boat was holed, the alarm was finally raised and a search began for survivors.

Ms Wilkinson and Mr Lawton were reunited in Bima. The tourists with the dinghy were found on Sunday night, but two, both from Spain, are still missing — they had set out for the swim about 30 minutes after Mr Lawton. There are stories that they were spotted on Sangeang Island, but they have never been found.

"I just want to warn people about the safety of these trips," Ms Wilkinson says. "Take your own personal locator beacon; check they've got life jackets, communications if something goes wrong."

Says Mr Lawton, "Ask what safety equipment is on board and if it's not adequate, say 'No'."