A massive underwater rock, the legendary Chimney, whale sharks and barracuda tornadoes — all in one place
Sail Rock, or Hin Bai (หินใบ), is a massive granite pinnacle located in the open sea between Koh Phangan and Koh Tao islands. The rock rises from 40 meters depth and protrudes approximately 15 meters above the water surface, resembling a sail — hence the name. This is undoubtedly the best and most famous dive site in the entire Gulf of Thailand, attracting divers from around the world.
Sail Rock offers dives for every skill level. The shallow section at 5–12 meters is ideal for beginners — vibrant corals, schooling fish, anemones with clownfish. The mid-zone at 12–18 meters features the Chimney entrance and main barracuda schools. Deep walls at 18–40 meters are territory for large pelagics, gorgonians, and potential whale shark encounters.
Sail Rock is located in the open sea approximately 20 km north of Koh Phangan and 15 km south of Koh Tao (coordinates: 9.6871°N, 100.0248°E). Due to its distance from shore, there is virtually no land influence on water clarity, and visibility often reaches 20–30 meters. The open location also makes Sail Rock a magnet for large pelagic fish and whale sharks migrating through these waters.
The main rock is surrounded by several smaller underwater pinnacles, forming an entire reef complex. The main wall on the eastern side drops vertically to 30+ meters and is covered in soft corals and sea fans. The western side is more gradual, with terraces and ledges where groupers and moray eels hide. To the south — a sandy bottom at 35–40 meters where rays sometimes rest.
The Chimney is a unique vertical crevice running through the rock from approximately 18 meters depth to 5 meters. It is one of the most famous swim-throughs in Southeast Asia and the primary reason divers return to Sail Rock again and again.
The Chimney entrance is located on the eastern side of the rock at about 18 meters depth. The opening is wide enough — approximately 2 by 3 meters — to allow one diver with full gear through. Schools of glassfish and cardinalfish usually swirl near the entrance. The instructor enters first and waits inside, guiding you with hand signals. The moment you peer inside and see the blue light filtering from above — unforgettable.
Inside the Chimney you gradually ascend vertically for about 13 meters. The crevice walls are covered in soft corals, sponges, and small marine life. Sunlight penetrates from above, creating magical beams through the water column. The channel width allows comfortable ascent but requires good buoyancy control — you must not touch the walls or damage corals. This is one of those moments in diving when you truly feel like an explorer.
The Chimney exit is in the shallows, at approximately 5 meters. You emerge from the crevice into the sunlit shallow reef — the contrast after the semi-darkness inside the rock is incredible. Schools of batfish often greet you here, hovering peacefully near the surface. Good buoyancy control is essential — BCD in order, steady breathing. We recommend neutral buoyancy throughout the entire ascent.
Sail Rock is a true oasis of life in the open sea. This solitary rock attracts an incredible diversity of inhabitants — from tiny nudibranchs to giant whale sharks. Every dive here is a kaleidoscope of colors and impressions.
Sail Rock is the best place in the Gulf of Thailand to encounter whale sharks. These majestic giants — the largest fish on the planet, reaching 12–18 meters in length — appear near the rock primarily from March to September, attracted by plankton-rich waters. Whale sharks are completely safe — they feed exclusively on plankton and small fish. Coming face-to-face with them underwater is a life-changing experience.
Huge schools of chevron barracuda are one of Sail Rock's signature sights. Hundreds of silver predators form spinning columns — 'tornadoes' — that rise from depth to the surface. The spectacle is so impressive that sometimes the schools completely block out sunlight. Barracuda are present at the rock virtually year-round and are completely safe for divers — you can hover nearby and enjoy this underwater ballet.
Several giant groupers weighing up to 100 kg permanently reside at Sail Rock — they are so accustomed to divers that they allow you within arm's reach. Large schools of batfish hover near the rock's summit, curiously observing divers. Blue-spotted stingrays, giant moray eels, octopuses, and numerous nudibranch species also live here — a paradise for macro photographers.
The walls of Sail Rock are covered in luxurious soft corals, gorgonians, and sea fans in every shade — from bright yellow to deep purple. Hard corals with clownfish in anemones dominate the shallow sections. Nudibranchs hide among the corals — dozens of species of colorful mollusks, each a work of underwater art. Underwater photographers can spend an entire dive shooting macro on just one square meter.
We organize regular day trips to Sail Rock from Koh Samui. Morning departure, evening return. All inclusive: transfer, boat, equipment, lunch, instructor.
From Bangrak pier in Samui to Sail Rock is approximately 1–1.5 hours by speedboat depending on weather conditions. Departure at 7:30 AM. Briefing and equipment preparation on board en route. Arrival at the rock by 9:00–9:30 when conditions are usually ideal — calm water and excellent visibility. Transfer paid separately or self-arranged.
Price includes: hotel transfer, boat trip, full equipment set (BCD, regulator, 3mm wetsuit, mask, fins, weights), 2 dives, lunch and drinks on board, professional dive master or instructor.
Book NowThe best period for diving at Sail Rock. Calm sea, maximum visibility — 15 to 30 meters. Water temperature 28–30°C. Minimal currents, ideal for less experienced divers. This is also the main whale shark season — plankton-rich waters attract them to the rock. During this time Sail Rock shows itself at its finest: vibrant corals, crystal-clear water, guaranteed barracuda school encounters.
October–February is monsoon season with higher waves and stronger currents. Visibility drops to 5–15 meters due to increased plankton levels. However, this season has its advantages: the abundance of plankton increases whale shark encounter chances. Currents bring more pelagic life — jacks, tuna, occasionally manta rays. Diving during this period suits experienced divers comfortable with currents. Sail Rock trips run when weather conditions permit.
Water at Sail Rock is warm year-round. In high season (March–September) temperature consistently holds at 28–30°C — you can comfortably dive in a thin 3mm wetsuit or even without one. In winter months (December–February) temperature at depth may drop to 26–27°C, but even then the thermocline is rarely uncomfortable. Warm water means longer dives and maximum comfort.
Divers with PADI Open Water Diver certification (or equivalent) can dive the outer walls of Sail Rock to 18 meters. Here you'll find the main barracuda schools, batfish, vibrant coral gardens, and the shallow reef. Even without the deep sections, the experience is incredible — most of Sail Rock's life is concentrated at 5–18 meters depth. Beginner divers and DSD (Discover Scuba Diving) participants dive under constant instructor supervision.
Advanced Open Water Diver certification is required for dives below 18 meters. Sail Rock's deep walls (18–40m) are home to large gorgonians, sea fans, huge groupers, and potential whale shark encounters. Here you can see life that rarely rises to the surface. The Chimney entrance also begins at 18 meters, so AOWD level is recommended for the full Chimney passage.
Navigating the Chimney requires good neutral buoyancy control. Inside the crevice you must not touch the walls — they are covered with fragile corals and sponges. A diver should be able to hover motionless in water, control ascent through breathing, and not panic in confined spaces. If you're not yet confident in your buoyancy — we recommend taking the PADI Peak Performance Buoyancy specialty course before your Sail Rock trip.
PADI SpecialtiesSail Rock day trips run daily in good weather. Book in advance — spots are limited! We work with small groups for maximum comfort.
