Thailand Anchoring Guide: Two Seas, Opposite Seasons

Two Seas, Two Calendars

The monsoon is not a storm; it is a season-long wind direction, and Thailand's two coasts sit on opposite sides of it. The north-east monsoon blows offshore on the Andaman side and onshore on the Gulf side; the south-west monsoon does the reverse. Everything below follows from that table:

Note the last row. In practice “sailing Thailand” means the Andaman side in the north-east monsoon, and this guide is weighted that way. The Gulf is real, and the trick of it is that the same island has a season on each side — Samui's Chaweng faces east and is sheltered in the south-west monsoon, Bophut faces north and is not; Haad Rin on Phangan has a Sunrise beach for one monsoon and a Sunset beach for the other. But you will not casually pop across: from Phuket to Samui by sea is well over a thousand miles round the peninsula through Singapore. Boats that stay in Thailand all year mostly stay on the Andaman side and choose their bays by the handful that shelter from the south-west — Ao Po, Ao Luk, the Lanta strait — or go into a marina.

Clearing In: No Permit, One Building, and the AIS Rule

Thailand asks less than its reputation suggests and one thing more. There is no cruising permit. What you get is a Customs temporary import for the boat — six months, extendable on application, and boats routinely stay far longer — an Immigration stamp for each person aboard, and a Harbour Master clearance. At Ao Chalong on Phuket's south-east corner the three offices share one building by the pier, which is why almost everyone clears there; the other ports of entry are Krabi, Koh Samui, Satun, Pattaya and Bangkok. Bring the ship's registration, passports, last port clearance, a crew list, and be ready for small fees at each window (a few hundred baht, more at weekends). Everyone aboard files a Thailand Digital Arrival Card online within three days before arrival. And here is the thing more: since October 2015 the Marine Department has required every foreign yacht to carry a Class B AIS transponder and keep it switched on in Thai waters (it may be off in a marina or on the hard). Boats without one have been refused clearance out. A copy of the AIS certificate goes in the paperwork.

Crew visas are the part that changes. Yacht arrivals at Ao Chalong have long been stamped in for 30 days, with the captain marked as such and other crew on a separate crew document; a tourist visa obtained in advance, extendable once by 30 days, has been the sailor's answer for a longer stay. From 15 September 2026 the general visa exemption for the 60 nationalities that still have one drops from 60 days to 30 days (extendable once by 30), so arriving by air to join a boat now gives no more than arriving by sea did. If crew leave the boat and fly out, tell Immigration first — the crew document is not a normal entry stamp and departing without converting it causes trouble at the airport. Costs at anchor are otherwise small: anchoring itself is free everywhere outside the parks, and the parks charge per head, not per night, as set out below.

Phuket and Phang Nga Bay: Mud, Karst and the Tide

Ao Chalong is the hub: a wide bay in 2–6 m of mud with good holding, the customs pier, the yacht club, a fuel barge and every marine trade, busy with longtails and tour boats by day and quiet by night. Anchor clear of the pier channel and remember the tide. Round the southern tip, Nai Harn is the island's prettiest anchorage in the north-east monsoon — sand in 3–10 m, a beach, a lake behind it — and completely untenable from May to October; Kata and Rawai (very shallow: 1–4 m, some of it drying) are its neighbours. The east coast is the Phang Nga side and the character changes: Ao Po is a mud-bottomed inlet with excellent holding and near all-round shelter, the marina at its head and the launch point for the bay. Phang Nga Bay itself is the reason people come — hundreds of limestone karst towers rising sheer from green water, with hidden lagoons (hongs) inside them that you reach by kayak through sea caves at mid-tide. The anchorages are in 3–10 m of mud with good holding, sheltered by the islands from most directions, and the whole bay is Ao Phang Nga National Park: a per-head fee, some zones closed to protect mangroves and seagrass, the Moken sea-people villages to be left alone. Koh Panak and Koh Hong have the best hongs; James Bond Island (Khao Phing Kan, with the pinnacle of Koh Tapu) is mobbed by tour boats from 09:00 to 16:00 and empty before and after, which is the argument for anchoring overnight. Ao Luk, deep in the mangroves at the north end, is one of the few Andaman anchorages that works all year. The Yao islands between Phuket and the bay are quiet Muslim fishing communities with sand-and-mud bays on their west coasts. See the Phuket & Phang Nga Bay anchorages — starting with Ao Chalong, Nai Harn and Ao Po.

Krabi, Phi Phi and the Trang Islands

East across the bay the karst comes ashore. Railay is a peninsula cut off from the mainland by cliffs and reachable only by sea, a climbers' village between two beaches: Railay West faces the sunset and any westerly swell, Railay East is the mangrove side and the calmer overnight in 3–15 m. Ao Nang next door has the town and a beach that dries a long way out — anchor in at least 4 m at low water. Then the Phi Phi group, 20 miles offshore and the most visited islands in the Andaman. Ton Sai Bay on Phi Phi Don is the harbour, a south-facing sandy bay in 4–18 m sheltered from the north-east monsoon with the village, the ferries and a great deal of wash; the other anchorages round the island are fair holding in sand between coral heads, so snorkel before you trust them. The whole group is Hat Noppharat Thara–Mu Ko Phi Phi National Park, and its rules are enforced.

Which brings us to Maya Bay on Phi Phi Leh, the beach from the film. It was closed in June 2018 after years of tour boats anchoring on the reef, and when it reopened in 2022 it did so with the bay itself closed to boats: nothing enters, nothing anchors. Visitors land at a floating pier at Loh Samah on the back of the island, walk a boardwalk to the beach, pay the park fee, stay about an hour and may wade in to the knee — no swimming. The bay closes completely from 1 August to 30 September each year for reef recovery. Your own boat waits off Loh Samah with the tour fleet; Phi Phi Leh's other coves are no-anchoring too. Our Phi Phi Leh page exists to say so.

South of Phi Phi the crowds thin with every island. Koh Lanta is long and low with a west coast of beaches for the north-east monsoon and a strait between Lanta Yai and Lanta Noi that shelters in anything; Ban Sala Dan at the north tip has fuel, food and a customs post for boats heading to Malaysia. Then the Trang islands of Hat Chao Mai National Park: Koh Ngai, Koh Mook — whose Emerald Cave (Tham Morakot) you swim through in the dark to a lagoon open to the sky, and which fills completely at high water — and Koh Kradan, fair holding in sand between coral off a beach that regularly tops the world's-best lists, at its flattest in February. Koh Bulon Leh is the last Thai island before Langkawi, a day away, and the place to have your clearance in order. See the Krabi & Phi Phi anchorages — starting with Railay Bay, Ton Sai Bay and Koh Lanta.

The Gulf: The Other Season

The Gulf islands are where the calendar flips. In the south-west monsoon, when Nai Harn is unusable, Samui's east-facing Chaweng is a sandy anchorage in 2–8 m in the lee of the island; Bophut on the north coast and Big Buddha Bay are the settled-weather alternatives, and Na Thon on the west coast is the port of entry. On Koh Phangan, Thong Sala is the ferry harbour and Haad Rin has a beach for each monsoon — Sunrise for the south-west, Sunset for the north-east — and once a month the Full Moon Party, which from a boat means noise, light and floating debris from dusk to dawn. Koh Tao is Thailand's dive island: Mae Hat Bay on the west coast in 3–15 m of sand and coral, fair holding, ferries and dive boats all day and squid boats lighting up the horizon all night; Koh Nang Yuan next to it is three islets joined by sandbars. Sail Rock (Hin Bai), the whale-shark pinnacle halfway to Phangan, is an open-ocean dive site — a day stop on a buoy in settled weather and not an anchorage in any normal sense. Ang Thong Marine Park north-west of Samui is 42 karst islands with a per-head fee and park buoys, and it closes for the Gulf's own monsoon from about 1 November to 15 December. Far to the north the islands off Sattahip near Pattaya — Koh Khram, Koh Chan, Koh Samae San and others — belong to the Royal Thai Navy and are closed to anchoring altogether. See the Koh Samui & Gulf anchorages — starting with Bophut and Koh Tao.

The Park Calendar: Who Closes When, and What It Costs

Most of the Andaman cruising ground lies inside a marine national park, and each park has a fee, a season and a rule of its own. Put together, they are the second calendar you sail by:

Three things about the table. First, the fee is per person per day, not per boat per night — four aboard in the Phi Phi group is 1,600 baht a day before a small vessel charge, and operators report that an overnight stay is counted as two days. Second, since 15 October 2025 six of these parks — Phi Phi, Ao Phang Nga, Than Bok Khorani, Similan, Surin and Lanta — have sold e-tickets through the QueQ app and the Department of National Parks website; you pay, get a QR code and show it to the ranger boat that comes alongside, which it does. Third, the closures are the south-west monsoon written into law: the Similans and Surins shut on 15 May, Koh Rok on 1 June, Maya Bay on 1 August, and the Gulf's Ang Thong shuts in November when the Andaman parks reopen. Underneath all of it is one rule that applies everywhere with a reef: anchoring on coral is a criminal offence. In the clear water of the north-east monsoon there is no excuse — look over the bow, or swim, and drop on sand.

Why an Anchor Alarm Matters Here

Thailand's failure mode is not wind. In season the Andaman is one of the gentlest cruising grounds on earth, and the boats that come to grief here do so in flat calm. The first reason is the tide. The Andaman range is 2–3 m, semi-diurnal, and the anchorages are shallow — 3–5 m at low water is normal in Ao Chalong, Rawai, Ao Nang and most of Phang Nga Bay. That does two things to a boat that has not moved:

So the working rule is the Bahamas one turned inside out: lay chain for high water and set the alarm for low. In the karst channels of Phang Nga the stream runs hard enough that the boat swings through the whole circle twice a night in no wind at all, which is why an alarm centred on the boat's position at bedtime will either wake you for nothing at 03:00 or, if you widen it to stop that, miss a genuine drag. Centre it on the anchor, size it for rode plus boat, and let the tide walk you round. The second reason is the bottom: outside the mud bays, Thai holding is “fair” in our data more often than in any Mediterranean country — sand between coral heads at Phi Phi, Kradan, Ngai, Hong, Koh Tao — and an anchor that sets well in a patch of sand can still walk off it when the tide turns it through 180 degrees. The third is wash. From 09:00 to 16:00 the famous bays fill with longtails and speedboats, and the temptation, as in Naples, is to widen the radius until the wash stops triggering it; a radius that ignores wash ignores drag too. Leave it, and put up with a daytime alert or two.

That is what a GPS anchor alarm is for, and this is the country where it earns its keep on calm nights rather than wild ones. Our per-anchorage figures run from 60 m in shallow Rawai and 65 m in the mud of Ao Luk to 100 m at Sail Rock, where the honest advice is not to stay at all — and GPS accuracy for anchor alarms explains how to set a radius that ignores swell and wash but catches drag. Every anchorage page on the Thailand hub carries one, and the spring tide week is when to believe it.

Beyond Thailand

The Andaman season is a corridor as much as a place. Langkawi in Malaysia is a day south of Koh Bulon Leh — duty-free, marina-rich, and the easy answer to a Thai visa running out — and boats bounce between the two all winter. The Similans and Surins lie 50–60 miles north-west of Phuket and are the finest diving in the country, with the permit, the cap and the closure above. Beyond them, Myanmar's Mergui Archipelago opens to yachts with an agent and a permit, and is as empty as Phang Nga is full. Our Bahamas anchoring guide is the other place in this series where the tide, not the wind, decides where your boat lies — the two make a useful pair.

The Bottom Line

Pick the coast, and the season picks itself: the Andaman from November to April, the Gulf from May to October. Clear in at Ao Chalong with your AIS transmitting and your arrival card filed, and forget about a cruising permit because there isn't one. Buy the park e-ticket, drop on sand or mud and never on coral, give Maya Bay its boardwalk and the Navy its islands, lay chain for high water — and run a GPS anchor alarm every night, centred on the anchor and sized for low water, because in Thailand the boat that drags is usually the one whose crew slept soundly in a flat calm while the tide turned it round.