Gulf of Thailand Deep Dive: Eastern Andaman Alternative
Every sailor who has been to Phuket has heard the complaint: the Andaman Sea from November to April is magnificent, but the charter fleets are dense in December and January, the anchorages at Phi Phi Don can be overrun, and the long-tail boat traffic in Phang Nga Bay makes quiet contemplation a challenge. The Gulf of Thailand, on the other side of the Malay Peninsula, offers a counterpoint. The sailing conditions are gentler — the gulf is more enclosed, the swell is smaller — but the scenery is no less dramatic. Limestone karst islands rise sheer from the water at Ko Samui's outer neighbours, mangrove-lined channels penetrate deep into jungle-clad shores on Ko Chang, and Ko Tao sits in the middle of a relatively sheltered stretch of water that is famous among divers for its whale sharks, bull sharks, and visibility to 30 metres.
The Gulf's Two Seasons
The Gulf of Thailand operates on a monsoon calendar that is roughly the inverse of Phuket's. The northeast monsoon from November to February brings the best conditions: winds from the northeast at 10-20 knots, settled weather, and pleasant temperatures around 28°C. The southwest monsoon from May to October brings rain, stronger winds, and the risk of heavy squalls, especially around the Ko Samui-Koh Phangan area which sits squarely in the path of the northeast monsoon's precipitation. Ko Samui receives significant rain in November and December — heavy enough that the tourist industry calls it "low season" — yet this is actually when the sailing conditions are at their most interesting.
Ko Samui and Ko Phangan
Ko Samui is the Gulf's primary sailing hub. Nathon pier on the island's west coast is the main ferry landing, but the yacht anchorage at Bophut on the north coast offers better holding in northeast conditions. The small commercial harbour at Nathon can accommodate visiting yachts for fuelling and provisioning. Ko Samui has full-service marina infrastructure at Samui Yacht Club and at the resort marinas along the west coast.
Ko Phangan, 12 nautical miles to the north of Ko Samui, is better known for the Full Moon Party at Hat Rin on its southeast coast, but the northwest coast anchorages — particularly Ao Chaloklam and the bay near Thong Sala — offer comfortable holding in northeast monsoon conditions. The island's interior remains largely forested and the northern coastline has several secluded beaches accessible only by sea.
Between the two islands lies the shallow channel of Ko Tan, a small satellite island with a fringing reef that creates a protected patch of water suitable for snorkelling and calm weather anchorage.
Ko Tao: The Dive Island
Ko Tao sits about 40 nautical miles north-northwest of Ko Phangan, requiring a passage that crosses open gulf water. The island is small — just 21 square kilometres — but punches far above its weight in terms of diving quality. The waters around Chumphon Pinnacle (northwest of the island), Southwest Pinnacle, and Sail Rock (between Ko Tao and Ko Phangan) are widely regarded as the best dive sites in the Gulf of Thailand, with whale shark encounters possible year-round. The anchorage at Mae Hat Bay on Ko Tao's southwest coast is the main stopping point; holding is reasonable in sand but can be uncomfortable when swell wraps around the southern point.
Ko Chang and the Eastern Gulf
Ko Chang — not to be confused with Ko Chang near Trat in the far east of the Gulf — refers here to the area around the Trat Province archipelago, which sits near the Cambodian border and is significantly less visited than Ko Samui. The islands of Ko Wai, Ko Mak, Ko Kham, and Ko Chang itself offer a progressively wilder experience as one moves east. Ko Wai has crystal-clear water and a largely reef-protected anchorage. Ko Mak has a quiet community of resorts and fishing families, with anchorage in the west coast bay. Ko Chang, at 429 square kilometres, is the largest island in the group and offers long stretches of undeveloped beach and mangrove channels in its southern reaches.
The mangrove system on Ko Chang's south coast, particularly around Ao Salak Phet, penetrates several kilometres inland along tidal creeks. Dinghy exploration of these channels at high tide reveals a world of monitor lizards, kingfishers, and the tangled root systems of Rhizophora mangroves stretching down to the waterline. The village of Ban Salak Phet, accessible by dinghy from the main anchorage, is an authentic working fishing community with excellent fresh seafood.
Sailing the Khao Sam Roi Yot Coast
On the western Gulf coast, the sailing grounds off Prachuap Khiri Khan and the Khao Sam Roi Yot National Park offer limestone karst scenery that rivals anything in the Andaman Sea. The coastline here — sheltered from northeast winds by the narrow peninsula — provides reliable flat water from November through February. The park's name means "three hundred peaks" and refers to the limestone pinnacles that rise to 605 metres above sea level at Sam Roi Yot mountain. Small fishing communities and prawn farms line the coast; fuel and basic provisions are available at Prachuap Khiri Khan town, 30 kilometres by road from the nearest anchorage.
Provisioning and Services
Ko Samui is the best-equipped sailing base in the Gulf of Thailand, with a well-stocked chandlery at Samui Yacht Club, diesel and water available, and a range of marine service providers covering haul-out, antifouling, and mechanical work. Beyond Ko Samui, provisioning becomes increasingly improvised — village markets, fishing boats selling their catch, and occasional supermarkets in larger towns. Fresh tropical fruits — mangosteen, rambutan, durian, and langsat — are available roadside throughout the eastern Gulf islands from July to September.
Explore on the Map
The Gulf of Thailand basin — from the northern shores near Bangkok through Ko Samui and Ko Tao to the Cambodian coast near Ko Chang — is fully visible on the map. Compare its enclosed character with the open Andaman Sea to the west, and trace the inter-island distances between Ko Samui, Ko Phangan, and Ko Tao. The Gulf of Thailand on the map reveals the scale and the logical passage sequence through this underrated sailing ground.