It’s no-frills diving: we’ve each got a couple of tanks on the wooden longtail boat, enough for two dives. We roll off the side of the longtail into silty water that’s warm enough for a shorty wetsuit.

Long sea plumes rise up from the ocean floor as we descend. Fifteen metres below the ocean surface, a remora follows us, circling my head and body, looking like a tiny upside-down shark.

The water teems with colourful tropical fish, including banner fish, parrot fish, puffer fish, and thousands of small silver fish that look like a rain shower. We startle a stingray that zooms off along the sandy ocean floor. Approaching the end of the dive, vying for attention, as we watch a moray eel peep out of a hole, the remora returns. “Remora, or suckerfish, usually attach to sharks or whales or very big fish,” Yad says, back on the longtail. It’s part of a symbiotic relationship. “Maybe it thought we were big fish.”

Part of the reason I’ve come to these largely Muslim islands (in a country that’s 95 per cent Buddhist) is that I’d heard they were like Thailand as it was 30-40 years ago, before the mainstream tourist crowds hit. This is a region with no big chain hotels, no inebriated Full Mooners, no stalls selling ‘same same but different’ T-shirts, no sleazy bars. Here, the pace is slower, the prices are (generally) lower, and you get beautiful beaches, forested hills and clear blue ocean, as well as one of the world’s largest populations of the rare and endangered dugong (sea cow), but no crowds.

One reason the area’s not so busy, says local tour operator Ekkachai Binwaha, is because the islands and mainland coastline are protected as part of Hat Chao Mai National Park, meaning it’s difficult to build big hotels and resorts.

“People come to Trang who are looking for a quiet place, people who don’t like Phuket and crowded places,” he tells me. “They’re explorers. It’s more adventurous here.”

We board a boat with him from Pakmeng Pier, and I soon feel the charm of the islands as we chug across the rolling blue Andaman ocean, past limestone karsts jutting out of the water. Our destination is Morakot Cave (or Emerald Cave) on Koh Mook, one of the Trang Islands’ most popular day trips. We float in life vests through an 80-metre tunnel, reaching daylight on the other side, and a small greenish pool walled in by steep cliffs. Rumour has it that pirates once used the Emerald Cave to hide their treasure.

I take another longtail “taxi” across to Koh Mook a couple of days later to meet guide Taord Bangjak (nicknamed Ood). At Farang Beach, we pick up a pair of kayaks and head out on the lively ocean.

Waves bash against barnacle-encrusted rocks as we paddle around the island. We pass the entrance to the Emerald Cave and, further along, empty Sabai Beach. Sun beats down on the island’s limestone crags and forests.

After two hours of paddling, we reach Koh Mook pier and stop for lunch in the little village, which is busy with locals running errands on motorbikes – women and girls wearing headscarves, the men in white taqiyah (prayer hats). As we tuck into spicy prawn curry and rice, one of the daily calls to prayer sounds out across the island.

Yad and I motor across to Hin Nok the next day, the calm ocean mirroring the pale blue of the cloudless sky. We put the anchor in at a cluster of black rocks poking just above the ocean surface, the summit of an underwater coral island. Under the water, a pair of moray eels watch us from a crack in the coral. Yad points to a big squid hovering in the water, such an elegant thing to make fried food from.

The ocean around Thailand’s west coast is one of the best places in the world to see endangered dugongs, especially around the Trang islands, which have the seagrass they feed on. “There are around 100 dugong around Libong and the Trang islands,” Yad says. There are several local myths about the creatures, including one that claims a dugong’s tears can make the object of your affection fall in love with you.

We hire a couple of motorbikes and set off around Libong island, following signs for Dugong Point . It’s quite an adventure course to get to the top, first hiking along a forest trail, then through an exciting cave system, the rock walls turned green with moss, before clambering over hard jagged volcanic rock.

From a wooden viewing platform, we have an open view of the ocean, the forests covering the island, the pier at Na Baan village that sticks out into the sea, as well as surrounding islands like Koh Laoliang and Koh Petra.

For half an hour, we watch the shining ocean, as swallows loop around the limestone cliffs, but we have no luck spotting dugongs. It’s only a minor disappointment, as the fun climb and the outstanding view from up here on the platform was time well spent.

We hike down and, unexpectedly, from a ledge at a cave opening, Yad spots a dugong far below. From up here it’s just a brown speck – not exactly the world’s greatest wildlife encounter, but still a sighting.

Yad shows me around the rest of the island. We ride into the village, with stilted houses close to the waterfront, the local mosque and the pier, where local women in headscarves sit shelling tubfuls of fresh crab. We follow a thin trail through a forest to a ‘secret beach’. There are a handful of fishing boats out on the water, but the beach itself is deserted.

The call to prayer goes out across the island from the mosque in the evening. With a nearly full moon out above me, the skies turn pink and red. I can’t recall any other Thai islands I’ve seen that are this quiet, or where life’s as simple as a cold beer, a good fish curry and the sound of waves breaking softly on the beach.

Getting there:

Graeme Green travelled with Trang Island Hopping Tour (trang-all-tour.com), who arrange excursions and holidays on the Trang islands.

Thai Airways (thaiairways.com) have return flights from Hong Kong to Krabi, an hour’s drive from Trang or Pakmeng Pier for boat trips to the islands. It’s also possible to fly from Bangkok directly to Trang.

Staying there:

Koh Hai Fantasy Resort (haifantasy.com), Charlie Beach Resort on Koh Mook (kohmook.com) and Libong Beach Resort (libong-beach.com) are good bases from which to explore the Trang islands.

For more information: tourismthailand.org or trang-islands.com.