Located between Koh Tao and Koh Phangan, Sail Rock (Hin Bai) is widely considered the best dive site in the Gulf of Thailand. With dramatic vertical walls, the famous Chimney swim-through, and the chance to encounter whale sharks, this world-class pinnacle offers an unforgettable diving experience for both advanced and adventurous Open Water divers. Easily reached on a day trip from Koh Tao or Koh Phangan, Sail Rock delivers crystal-clear visibility, vibrant marine life, and thrilling currents—making it a must-do for any scuba diver exploring Thailand.
Meet Sail Rock (AKA: Hin Bai)
Located about an hour by boat from Koh Tao, Sail Rock is Thailand’s best-known dive site in the Gulf. It’s a submerged pinnacle surrounded by deep blue and bursting with life. It’s not a resort island or a beach bar. There are no hammocks or cocktails. In fact, it doesn’t offer anything above water beyond a vaguely photogenic silhouette and the occasional resting seagull.
Underwater, though, it’s a riot of marine action: enormous schools of barracuda swirl like silver hurricanes, batfish float past like confused dinner plates, and the occasional grouper lumbers by looking like he’s got an overdue tax bill.
And then there’s The Chimney.
The Chimney (A Vertical Tunnel and a Minor Existential Crisis)
Sail Rock’s pièce de résistance is a narrow vertical swim-through known as The Chimney. It starts at around 18 metres and spits you out somewhere closer to 5, assuming you don’t panic, reverse, or get mildly claustrophobic halfway through (all of which I’ve been told are completely normal reactions).
I gave it a go, obviously. Because when someone offers you the chance to wriggle through a rock tube 18 metres below the ocean surface, you say yes. That’s just science.
Emerging at the top of The Chimney was one of those rare moments in travel where you feel triumphant, weightless, and utterly insignificant—all at once.
Currents, Fish, and That Rumour About Whale Sharks
The currents at Sail Rock can get a bit mischievous. Some days it’s like diving through a lazy river; other days it feels more like being inside a washing machine operated by Poseidon himself.
But the marine life more than makes up for it. On our dive, we floated through clouds of fusiliers, hovered near walls buzzing with cleaner wrasse and shrimp, and stared down a grouper the size of a small fridge.
And yes—whale sharks do visit here. It’s not guaranteed, but they show up often enough that most dive guides will casually say things like, “Keep an eye out—one was here last week,” before grinning enigmatically and adjusting their mask.
How to Dive Sail Rock (Without Losing Your Flip-Flops)
The best way to visit Sail Rock is by joining a dive trip from Koh Tao or Koh Phangan. I went with Big Blue Diving Koh Tao, who managed to make the entire experience feel like a floating house party, only with more neoprene.
They provided equipment, breakfast, lunch, and the sort of dive briefings that make you feel simultaneously excited and mildly nervous. (Which, let’s be honest, is the ideal pre-dive mood.)
Final Thoughts: Don’t Skip the Rock
I’ll admit it: I never thought a solitary rock in the middle of the sea would be one of the highlights of my travels through Thailand. But Sail Rock is a glorious reminder that the best adventures often lie just beneath the surface.
If you’re looking for the best scuba diving in the Gulf of Thailand, don’t be seduced by flashy beaches or bars named after pirates. Go for the rock. Dive the chimney. Get pushed around by the current. Spot a whale shark, or don’t—but enjoy the suspense. And then, when it’s all over, sip something cold back on land and tell anyone who will listen about that time you squeezed through a rock tunnel underwater and lived to tell the tale.
Need-to-Know Info
Dive Site: Sail Rock (Hin Bai)
Location: Between Koh Tao and Koh Phangan, Gulf of Thailand
Depth: 5–40 metres
Experience Level: Best for Advanced Open Water, or confident Open Water divers
Highlights: The Chimney swim-through, schools of barracuda, possible whale shark encounters
Best Time to Go: March–October for calm seas and best visibility
📅 Sail Rock Schedule by Month
We run Sail Rock trips every 3 days, and here are some key dates to help with your planning:
August: 2nd, 5th, 8th, 11th, 14th, 17th, 20th, 23rd, 26th, 29th.
September: 1st, 4th, 7th, 10th, 13th, 16th, 19th, 22nd, 25th, 28th.
October: 1st, 4th, 7th, 10th, 13th, 16th, 19th, 22nd, 25th, 28th, 31st.
November: 3rd, 6th, 9th, 12th, 15th, 18th, 21st, 24th, 27th, 30th.
December: 3rd, 6th, 9th, 12th, 15th, 18th, 21st, 24th, 27th, 30th.Please note we also dive at Chumphon Pinnacle ‘the morning after’ and also Southwest ‘the morning before’! 2 other great Koh Tao dive sites.
