Quick answer
The Similan Islands are open from about mid-October to mid-May. Most liveaboards leave from Khao Lak, two hours north of Patong, for three to five nights with up to four dives a day; four nights usually add Koh Bon, Koh Tachai and Richelieu Rock. You need at least an Open Water certificate, ideally Advanced. Expect roughly 25,000 to 45,000 THB for four nights, plus park fees.
The Similan Islands are a chain of granite islands about 60 kilometres off the coast of Khao Lak, north of Phuket, protected as the Mu Ko Similan National Park. Huge rounded boulders, white sand and water that is often clear to 20 or 30 metres make them the best-known diving in Thailand. They are open only part of the year, and the best way to dive them is to sleep on board: a liveaboard reaches the outer sites early, before the day boats, and adds Koh Bon, Koh Tachai and Richelieu Rock further north.
When are the Similan Islands open for diving?
The national park opens around 15 October and closes around 15 May, when the south-west monsoon makes the sea too rough and lets the reefs recover. Dates can move slightly from year to year, and the park can close a site or limit the number of visitors at any time. Inside the season, conditions change month by month.
| Period | Conditions | Highlights |
|---|---|---|
| Mid-October to November | Seas settling, some swell early on | Quieter boats at the start of the season |
| December to January | Calm and dry, very clear water | Peak season; boats fill up early |
| February to April | Calm, warm, plankton at times | Best chances of manta rays and whale sharks |
| Early to mid-May | Weather turning | Last trips; risk of cancellations |
| Mid-May to mid-October | Park closed | No diving in the Similans |
How long should a Similan liveaboard be?
Most trips last from three to five nights. A short trip stays in the Similans; four nights or more usually add Koh Bon and Koh Tachai, and the best itineraries go as far north as Richelieu Rock, near the Surin Islands. Boats leave in the evening from Thap Lamu pier in Khao Lak, or from Phuket for a longer crossing during the first night.
- 2 to 3 nights: the Similans only, around 10 to 12 dives. Good if your time is short.
- 4 nights: the classic trip, with Koh Bon, Koh Tachai and often Richelieu Rock, around 14 to 16 dives.
- 5 to 6 nights: more time at the northern sites, sometimes the Surin Islands, for experienced divers.
Transfers from Patong to Khao Lak take about two hours and are usually arranged by the boat. Plan one night in Patong or Khao Lak before departure if you fly in the same day, and keep a full day after your last dive before flying home.
What does a day on a liveaboard look like?
- Wake-up around 6:30 am with coffee and a briefing, then the first dive before breakfast.
- Breakfast, rest, then the second dive late in the morning.
- Lunch and a surface interval while the boat moves to the next site.
- Third dive in the afternoon, often the best light for photos.
- A sunset or night dive on most days, then dinner and an early night.
Expect up to four dives a day. You can skip any of them; many people do after a couple of days. Cabins are small, and shared bathrooms are common on mid-range boats. Bring seasickness tablets if you are prone to it, reef-safe sun protection and a light jacket for the evening breeze.
Which dive sites will you visit?
Elephant Head Rock
Granite boulders piled on top of each other, with swim-throughs and arches between them. Currents can be strong, so it is usually dived with an experienced guide. Look for schools of trevally and fusiliers along the rocks.
East of Eden and Christmas Point
Two of the best-loved reefs of the park: East of Eden for its sloping coral garden and small life, Christmas Point for its boulders and swim-throughs. Both are good for photographers.
Koh Bon
North of the Similans, Koh Bon has a ridge and a wall where manta rays are seen regularly in the season, most often from February to April. The current that brings the mantas can be strong, so stay close to your guide.
Koh Tachai
An offshore pinnacle with large schools of fish and a chance of mantas and whale sharks. The park has closed it in the past to let the reef recover, so check whether it is open for your dates before you choose a trip for it.
Richelieu Rock
A horseshoe-shaped pinnacle near the Surin Islands, covered in soft corals and famous for small creatures such as seahorses and harlequin shrimps. Whale sharks pass now and then between February and April. It is the highlight of many four-night trips.
How much does a Similan liveaboard cost?
Prices depend mostly on the boat, the cabin and the number of nights. Budget and mid-range boats share bathrooms and take more divers; more expensive boats have private cabins, fewer guests and better food. National park fees, equipment rental and nitrox are often charged separately, so add them before comparing.
| Option | Price per person (THB) | What to check |
|---|---|---|
| Day trip by speedboat from Khao Lak, 2–3 dives | 5,500–8,500 | Transfer from Patong, park fee, number of divers on board |
| Liveaboard, 2–3 nights, Similans only | 15,000–28,000 | Number of dives, cabin type |
| Liveaboard, 4 nights, with Koh Bon, Koh Tachai, Richelieu Rock | 25,000–45,000 | Whether Richelieu Rock is on the plan |
| Liveaboard, 5–6 nights | 35,000–60,000 | Itinerary and guide-to-diver ratio |
| National park entry and diving fees, per trip | 1,500–2,500 | Often not included, paid on board |
| Equipment rental, per day | 400–800 | Size and condition, dive computer included or not |
| Nitrox for the whole trip | 1,500–3,500 | Nitrox certification required |
What level do you need for a Similan liveaboard?
An Open Water certificate is the minimum on almost every boat, and some ask for a minimum number of logged dives. Advanced Open Water is strongly recommended: many sites go below 18 metres, currents are common and descents are often in blue water. Most liveaboards can run the Advanced course on board, using the trip dives. If your last dive was a long time ago, do a refresher in Phuket before you go.
Not certified yet? Start with our guide to learning to dive in Patong: a 3 to 4-day Open Water course before the trip works well, as long as you keep a day in between.
Liveaboard or day trip from Khao Lak?
A day trip is cheaper and needs no cabin, but from Patong it means a pickup around 5 am, two hours on the road, more than an hour by speedboat each way and only two or three dives, at the same time as the other day boats. A liveaboard costs more but gives you four dives a day, early dives before the crowds and the northern sites a day trip cannot reach.
- Choose a day trip if you have only one day, if you are not sure you will like it or if you get seasick at night.
- Choose a liveaboard if diving is the main reason for your trip and you want Koh Bon, Koh Tachai or Richelieu Rock.
How do you choose a liveaboard?
- Read the itinerary day by day and check which northern sites are included.
- Ask how many guests the boat takes and how many divers each guide leads.
- Ask whether park fees, rental, nitrox and transfers from Patong are included.
- Check the safety equipment: emergency oxygen, first-aid kit, radio, and a crew trained to use them.
- Ask what happens if the park closes a site or the weather cancels a day.
- Make sure your insurance covers liveaboard diving.
For the dive sites you can reach on day trips from Patong, including the King Cruiser wreck, see our guide to scuba diving from Patong.
Frequently asked
- Can a new Open Water diver go on a Similan liveaboard?
- Yes, most boats accept Open Water divers, but you will get much more from the trip with Advanced training or at least 15 to 20 logged dives, because many sites are deeper than 18 metres and have currents. Many liveaboards run the Advanced course on board during the trip. If you have just certified, tell the boat so they can place you with a guide who takes small groups.
- Can non-divers join a Similan liveaboard?
- On many boats, yes, as snorkellers, often at a lower price than divers. The Similans have good snorkelling in the shallow bays, but at offshore sites such as Koh Bon, Koh Tachai or Richelieu Rock there is little to see from the surface. A Similan day trip by speedboat from Khao Lak can suit a non-diving partner better.
- When is the best time to see manta rays and whale sharks in the Similans?
- Sightings are most frequent from February to April, mainly at Koh Bon, Koh Tachai and Richelieu Rock, when plankton in the water attracts them. They are wild animals and never guaranteed: some trips see several, others none. Choose a trip of four nights or more that includes the northern sites if they are a priority.