Hin Bai (Sail Rock)
Overview
Hin Bai, known internationally as Sail Rock, is a massive granite pinnacle that breaks the surface of the Gulf of Thailand roughly midway between Koh Phangan and Koh Tao. The rock rises from a depth of over forty meters to a peak that stands several meters above the waves, its underwater flanks covered in marine life and hosting the Gulf's most famous dive feature: a vertical chimney that penetrates the entire rock formation, large enough for divers to swim through from bottom to top. The boat ride from Koh Phangan took seventy minutes across flat, warm Gulf water, the rock appearing as a dark tooth on the horizon long before we arrived. Gearing up with the other divers, anticipation was palpable -- Sail Rock's reputation as the Gulf of Thailand's best dive site is well established, and the possibility of whale sharks had everyone scanning the surface for shadows. I dropped in on the rock's eastern face and descended along the granite wall, which was covered in a thick carpet of anemones, soft corals, and encrusting organisms that gave it a fuzzy, organic texture. Schools of yellowtail fusiliers parted around me as I descended, their streamlined silver bodies catching the filtered sunlight. At twelve meters, an enormous giant grouper held station in a recess in the rock, its mouth opening and closing slowly, its eyes following me with the resigned patience of an animal that has watched thousands of divers pass by. The chimney entrance appeared at eighteen meters on the rock's southern face, a dark opening in the granite roughly two meters in diameter. I entered and began a slow ascent through the vertical tunnel, the walls close but not claustrophobic, covered in cup corals and small tunicates. Looking up, the chimney narrowed slightly before opening to a bright circle of surface light at six meters. Emerging from the top felt like being born from the rock itself, a moment of exhilarating transition from enclosed space to open water.
Marine life
Dive profile
DEPTH PROFILE
DEPTH PROGRESSION & WAYPOINTS: Hin Bai (Sail Rock)
Location
Near Koh Phangan, in the Gulf of Thailand region of Thailand.
Frequently asked questions
How do I reach Hin Bai from Koh Phangan?
Hin Bai is located roughly midway between Koh Phangan and Koh Tao in the Gulf of Thailand. Dive boats depart from both islands, with the trip taking approximately 60 to 90 minutes from Koh Phangan and about 45 to 60 minutes from Koh Tao. Most dive operators on either island offer day trips to Sail Rock as their premium excursion. The site can also be visited from Koh Samui, though the boat ride is longer at around 2 hours.
What is the chimney at Sail Rock?
The chimney is a vertical tunnel that passes completely through the rock formation, with its lower entrance at approximately 18 meters and its upper exit at around 6 meters. The chimney is wide enough for divers to ascend through comfortably, and the experience of swimming upward through the rock with light filtering from above is one of the most iconic experiences in Gulf of Thailand diving. Buoyancy control is important as the chimney walls are covered in marine growth, and ascending too quickly can cause contact damage.
When are whale sharks most likely at Sail Rock?
Whale shark season at Sail Rock broadly spans from March to October, with peak likelihood during March to May and September to October. These periods correspond with plankton blooms in the Gulf of Thailand that attract whale sharks to the nutrient-rich waters around the pinnacle. Sightings are never guaranteed and vary significantly from year to year, but Sail Rock is considered the single most reliable site for whale shark encounters in Thai waters.
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Data Provenance
This profile is compiled from 3 operator submissions and 142 community logs. Key facts (depth, entry) are verified against official hydrographic charts.