Getting there
Speedboat or Catamaran to the Similans?
Seventy kilometres of open Andaman Sea, twice in a day. The difference between the two boats is mostly about your stomach.
Check dates and availability ↗Crossing Thap Lamu to the Similan Islands
| Speedboat | Catamaran | |
|---|---|---|
| Typical crossing time | About 60–90 minutes | About 90–120 minutes |
| Ride quality | Fast, can be bumpy in swell | More stable, smoother |
| Seating | Open, compact | Spacious, more shade |
| Best for | Time-conscious travellers, calm days | Families, seasickness-prone, early/late season |
| Distance covered | Around 70 km each way | Around 70 km each way |
The crossing is longer than people expect
The Similan Islands lie roughly 70 kilometres off the Phang Nga coast, which is genuine open water rather than a sheltered hop between headlands. There is no scenic coastline to watch on the way out; you leave Thap Lamu, the mainland drops away, and for the next hour or more you are on the Andaman Sea. This distance is why the park closes in the monsoon, why day trips start early and end late, and why boat choice matters more here than on a Phi Phi excursion where the ride is short and coastal.
What a speedboat actually feels like
Speedboats make the crossing in roughly sixty to ninety minutes and are the most common option by a wide margin. On a flat January morning the ride is exhilarating and gets you to the islands ahead of slower traffic. In any real swell it becomes physical work: repeated slamming as the hull crosses waves, spray, and no comfortable way to brace for an hour. Anyone with back trouble should think carefully, and it is worth sitting toward the middle or rear rather than the bow, where the motion is most violent.
Why a catamaran is often the better call
A high-speed catamaran takes noticeably longer — around ninety minutes to two hours — but the twin-hull design cuts the pitching and rolling that makes people ill. There is more room, more shade and somewhere to sit properly rather than being wedged on a bench. You lose perhaps half an hour at each end of the day; you gain a crossing that most people can eat lunch after. For families with young children, anyone prone to motion sickness, and for trips at the beginning or end of the season, the trade is usually worth making.
Sea conditions through the season
The park's open months sit inside the northeast monsoon, which brings dry weather and calmer water to the Andaman. Conditions are not uniform: December through February are typically the flattest, with the best underwater visibility, while late October and early May sit closer to the monsoon transitions and can serve up choppier crossings. Sea state is the real variable behind boat choice. On a calm day in January the difference between the two is half an hour. On a lumpy day in late October it is the difference between a good day and a miserable one.
Managing seasickness
Take motion-sickness medication before you leave your hotel, not at the pier — most over-the-counter tablets need thirty to sixty minutes to work. Eat something light rather than nothing. On board, stay where you can see the horizon, keep your head still against a headrest, and stay out of the cabin if there is one. Avoid reading and phone screens on the crossing. If you know you are badly affected, book a catamaran and a trip in the calm mid-season months rather than relying on tablets alone.