Sail Rock

Hin Bai, Sail Rock, is a granite pinnacle rising from about forty metres of water to break the surface roughly midway between Ko Tao and Ko Phangan, standing alone in open water with no other structure nearby - which is why it concentrates fish. It is consistently rated the best dive site in the Gulf of Thailand. Its distinctive feature is the chimney: a vertical shaft inside the rock, entered at around eighteen metres and exited near six, wide enough for one diver at a time, which is a genuine swim-through rather than a marketing description. Around the pinnacle are schools of trevally, barracuda, batfish and chevron barracuda in tornado formations, and whale sharks pass through, most often between March and May and again around September. There is no landing - it is a dive and snorkel site only. Currents can be strong and visibility varies; the chimney is not for anxious or inexperienced divers.

What's there

• The chimney - a vertical shaft through the rock from about eighteen to six metres.
• The schooling fish - trevally, batfish and barracuda around the pinnacle.
• The whale sharks - passing most often March to May and around September.
• The isolation - a single pinnacle in open water between two islands.

When to go

March to September for the best conditions and whale shark chances; it is diveable year-round but visibility and sea state vary. Boats run from Ko Tao, Ko Phangan and Ko Samui.

What to expect

Dive site only - no landing and limited value for snorkellers beyond the surface. Whale sharks are never guaranteed. The chimney is narrow and single-file, and unsuitable for anyone anxious in confined spaces. Currents can be strong.

Nearby

Ko Tao is north; Ko Phangan and Ko Samui are south.