Sail Rock — Hin Bai

Sail Rock is a day out rather than a place to stay. Boats leave in the morning from Koh Tao, Koh Phangan and Koh Samui, cross open Gulf water, then spend the rest of the day on one rock: two dives with the surface interval alongside it, lunch on deck, back in port by late afternoon. Because operators from three islands aim at the same pinnacle, it can be busy by mid-morning, and the crossing is exposed enough that trips get called off on the morning when the wind is up.

Underwater it is one structure rather than a list of sites. The rock keeps its shape below the surface, stepping down to sand at around 35 m, with boulder shoulders, ledges and undercuts on the way. The dive changes with the direction you circle it and where the current sits: one face swept and full of fish, the sheltered side quieter and better for small things, with most groups spiralling up from the deeper faces onto the shallow top.

The shaft through the rock sets the plan for most dives. Groups go through one at a time, usually with torches, and it is narrow enough that a diver out of trim silts it for everyone behind, so guides tend to run it early. The fish are the other half of it: barracuda hold in midwater off the pinnacle long enough that a group can plan an approach, trevally cut into baitfish against the rock, and the long shallow safety stop over the top is often the busiest part of the dive.

It suits divers already in the Gulf — on Koh Tao for a course, or on Phangan and Samui for the beaches — who want one serious dive day rather than a week of them. Current is moderate but noticeable on the open faces and there can be surge near the top, so it rewards people who can hold a depth without grabbing the rock. Wide-angle photographers do well out of it. Anyone wanting variety of terrain will not, since the day is the same pinnacle twice.