If you move north from the Similan archipelago, bypassing the island of Koh Bon, you can get to the most interesting dive site Koh Tachai. It is a lonely island with white sandy beaches. There are two dive sites there: Tachai Pinnacle, or Twin Peaks in the south and Tachai Reef, also known as Leopard Shark Reef in the east.
It is a pair of underwater peaks located 500m south of Koh Tachai and marked with buoys. They are covered in hard corals and sea fans. The southern peak is larger, its top is located at a depth of 12 m, has the shape of a dome surrounded by large boulders, and ends on a sandy bottom at a depth of 30-45 m. There are tunnels in its western part. The northern peak is lower, its top is at a depth of 18 m. Between the peaks there is a 50 m flat bottom covered with bushes and corals.
There are often strong currents around the southern summit, especially during the full moon and new moon. At such times, it is difficult to swim all the way around the cliff, so it is recommended to stay close to the cliff and not deviate from the path, otherwise you can spend a lot of air and energy. Divers should use the mooring line for descent and safety stops. You should also be extremely careful when lifting, given the busy flow of boats on the surface.
Of greatest interest to divers on Tachai Pinnacle are manta rays that swim in circles above the peaks. On the outside of the sandy area, several zebra sharks can be seen in one dive. It is also a favorite spot for whitetip and blacktip reef sharks and exotic ocean triggerfish for the Similan. Schools of barracuda, blue-finned caraxes, swallow fish, snappers and shooters hover around.
Tachai Reef stretches across the eastern side of the island from northeast to southwest, its slope begins at a depth of 5-10 m to a sandy bottom at a depth of 25-30 m. Hard corals predominate here: fire corals, brain corals, antlers and porites. In the southern part of the reef there are much less corals; its gentle descent turns into a wall with a steep slope, falling to a depth of 30 m.
Due to the shallow depth, the dive site is suitable for both day and night dives. Dive boats here have the opportunity to moor at night. The dive route is very simple: you need to go with the current along the reef and then return back to the boat. Current generally calm to moderate north-east to south-west.
Divers regularly spot zebra sharks and stingrays here lying on the sand by the reef, and sometimes in shallow waters. The reef is also home to blowfish, zebra fish, parrotfish and moray eels. After dark, several types of crabs and shrimps go hunting. There are many cuttlefish, nudibranchs, and flatworms. In addition, you can see a rare species of lionfish that hide in the crevices of the reef.
Diving on Tachai is included in the diving safari program on ships of different comfort. The duration of such a trip is at least 3 days / 2 nights on South Siam ships.