Diving in Thailand: The Similans, Koh Tao, and the Best Sites

Thailand is one of the great diving destinations in the world. The Andaman Sea has world-class dive sites (the Similans, the Surins, Koh Lipe, the Hin Daeng + Hin Muang pinnacle), the Gulf has the cheapest scuba certification on the planet (Koh Tao), and the liveaboard options are the best value in Asia. Here's the guide.

The two coasts (and the seasons)

The Andaman coast

The Indian Ocean, the dramatic limestone karst landscape, the most dramatic dive sites. The seasons:

• Best: November to March. The dry season, the calm water, the 15-30 m visibility. The peak season.
• Worst: May to October. The monsoon, the rough seas, the visibility drops. The Similans and the Surins close.

The Gulf coast

The South China Sea, the less dramatic, the more diver-training oriented. The seasons:

• Best: February to September. The dry season, the calm water, the 10-25 m visibility. The peak diving is June-August.
• Worst: October to December. The Gulf monsoon, the rough seas, the visibility drops. Some dive schools close.

The best sites

The Similan Islands (the headline, Andaman)

The 9-island national park 100 km northwest of Phuket, open November-May only. The dive sites:

• Richelieu Rock: The most famous dive in Thailand. The pinnacle that breaks the surface at low tide, the soft coral, the anemone gardens, the whale sharks, the manta rays, the seahorses. The most biodiverse dive in Southeast Asia.
• Koh Bon: The wall dive, the manta rays, the most consistent pelagic encounter.
• Koh Tachai: The pinnacle, the barracuda schools, the most active marine life.
• Elephant Head Rock: The swim-through, the soft coral, the most photographic.

How to do it: The day trip from Phuket or Khao Lak is rushed. The liveaboard is the way. The 3-day liveaboard (8-10 dives) is $400-800. The 4-day liveaboard (12-14 dives) is $600-1,200. The most popular boats: Manta Queen, Dive Race, The Junk.

The Surin Islands (the remote one, Andaman)

The 5-island national park 60 km north of the Similans, the least visited, the most remote, the Moken (sea gypsy) villages. The dive sites are similar to the Similans but less crowded. The 2-3 day liveaboard is the way. $400-800.

Koh Tao (the cert one, Gulf)

The 21-km² island 70 km north of Koh Samui, the cheapest place in the world to get a PADI certification. The dive sites:

• Chumphon Pinnacle: The most famous, 36 m deep, the visibility is 15-30 m, the barracuda schools, the pelagic fish.
• Sail Rock: The pinnacle between Koh Tao and Koh Phangan, the most consistent dive site in the Gulf, the whale sharks are sometimes here.
• Shark Island: The small island in the south, the granite boulders, the reef sharks (they're not dangerous), the swim-throughs.
• HTMS Sattakut Wreck: A former Thai Navy warship sunk in 2011, the most-photographed wreck in the Gulf.

How to do it: The PADI Open Water course is 4 days, $250-350, includes all gear, instruction, and 4 open water dives. The most popular schools: Big Blue, Crystal, Ban's, Roctopus. The Advanced Open Water is 2-3 days, $200-250. The Rescue Diver is 4 days, $400-500. The Divemaster is 6-8 weeks, $1,000-1,500.

Koh Phi Phi (the day trip one, Andaman)

The 2-hour boat trip from Phuket or Krabi, the most famous day trip. The dive sites:

• Bida Nok + Bida Nai: The two limestone pinnacles, the leopard sharks, the visibility, the most popular.
• Palong Wall: The wall dive, the most photographic.
• King Cruiser Wreck: A 100-m ferry wreck sunk in 1997, 30 m deep, the most famous wreck in Thailand.

How to do it: The day trip from Phuket or Krabi is $80-150 (2 dives). The liveaboard is not really necessary (the day trip is enough). The most popular operators: Sea Bees, Phi Phi Scuba, Dive Kampu.

Koh Lipe + the Tarutao (the southern Andaman)

The small island in the far south, near the Malaysian border, the Tarutao National Park, the most beautiful in the Andaman. The dive sites:

• Hin Daeng + Hin Muang: The two pinnacles 50 km south of Koh Lipe, the most famous, the manta rays, the whale sharks. The 3-4 hour boat trip is the way.
• Stonehenge: The pinnacle, the soft coral, the most active.
• 8 Mile Rock: The pinnacle, the barracuda schools, the pelagic.

How to do it: The day trip from Koh Lipe to Hin Daeng + Hin Muang is the most famous dive trip in southern Thailand. $150-200 per person (2 dives, full day). The liveaboard from Koh Lipe is also available.

Phuket + Khao Lak (the gateway)

Phuket and Khao Lak are the gateways to the Similan and Surin liveaboards. The day trip diving from Phuket includes the Racha Islands, Koh Phi Phi, and the King Cruiser Wreck. The Khao Lak dive shops are the most popular for the liveaboard departures.

How to choose an operator

• Look for a PADI, SSI, or BSAC certified school with a good safety record.
• Check reviews on TripAdvisor, Google, and the dive forums (Scubaboard, Divernet).
• Ask about the boat size, the dive group size, the safety equipment, the dive guide-to-diver ratio (1:4 is the standard).
• Avoid the cheapest options. The price is a signal. $20-30 per dive is the standard, less than that is suspicious.
• Make sure the operator has a DAN (Divers Alert Network) insurance partnership or recommends it. DAN is the standard dive insurance.

How to plan a diving trip

The 5-day "Koh Tao certification" plan

Day 1-2: Arrive Koh Tao, check into the school, do the theory and the pool sessions. Day 3-4: Open water dives (4 dives total, 2 per day). Day 5: Fun dive or relax, then ferry back to Samui or Phangan.

The 4-day "Similan liveaboard" plan

Day 1: Pickup from Phuket or Khao Lak, transfer to the boat, first dive in the afternoon. Day 2-3: 3-4 dives per day, including the famous Richelieu Rock. Day 4: Morning dive, return to Phuket or Khao Lak by afternoon.

The 7-day "combined Andaman + Gulf" plan

Day 1-3: Phuket + day trip to Koh Phi Phi. Day 4-6: Similan liveaboard. Day 7: Fly to Koh Samui or Koh Phangan. Day 8-10: Koh Tao for the cert or the fun dives.

What to bring

• PADI, SSI, or BSAC certification card (or the temp card if just certified)
• Dive log (the operator will want to see it)
• DAN insurance (or equivalent)
• Reef-safe sunscreen (the reefs are coral-fragile)
• A rash guard or a wetsuit (the water can be cool, the boats can be sunny)
• A reusable water bottle (dehydration is a real risk on dive boats)
• Motion-sickness pills (the Andaman in low season is rough)

What to know about safety

• Don't dive if you have a cold, a sinus infection, or a recent surgery.
• Don't fly for 18-24 hours after diving (the decompression sickness risk).
• Don't drink alcohol before diving.
• Stay hydrated, eat light, sleep well.
• Listen to your dive guide. They know the site.

What to know about the marine life

Thailand's reefs have been hit hard by the 2010 coral bleaching event and the over-tourism. The reefs are recovering, but they are not the pristine reefs of 20 years ago. The bigger fish (whale sharks, manta rays) are still around, but the encounter rate is lower than in the Maldives or the Galapagos.

The good news: the conservation work is real. Many operators are part of reef-cleaning projects. The national parks are strictly regulated. The marine life is recovering.

Cost (4-7 day diving trip, per person)

• Open Water course (Koh Tao): $250-350
• 2-tank day trip: $80-150
• 3-day liveaboard (Similans): $400-800
• 4-day liveaboard (Similans + Surins): $600-1,200
• Accommodation: $10-30/night (Koh Tao) or $50-150/night (Phuket)
• Total: $400-1,500

What to skip

• The "discover scuba" intro dives in Patong: The cheap intro dives in the package-tour area are not great. The proper PADI Discover Scuba is $100-150 and is a much better experience.
• The day-trip diving in peak season from Phuket to the Similans: The boat is 3+ hours each way, the dive is rushed, the visibility is the same. The liveaboard is the only way to do the Similans properly.
• The "cert in 2 days" courses: The proper Open Water is 4 days. The "express" courses are rushed, the safety is compromised.