Island hopping is the reason most people come to Thailand in the first place, and it is genuinely one of the easiest places in the world to do it. What catches people out is not the boats. It is the two things nobody plans for: picking the wrong coast for the season, and losing all signal at the exact moment they need a ferry ticket, a map, or a Grab. This guide covers how to build a sensible route, how the ferries actually work, and how to stay connected across islands where the signal is far less reliable than it is in Bangkok.
The one rule that shapes every trip: two coasts, opposite seasons
Thailand's islands sit on two different coasts, and they run on opposite weather clocks. This single fact decides your whole itinerary.
The Andaman coast on the west (Phuket, Krabi, Railay, Koh Phi Phi, Koh Lanta, and far-south Koh Lipe) is at its best in the dry season from roughly November to April, with the clear, calm water Thailand is famous for. From around May to October the southwest monsoon brings rough seas, ferries get cancelled more often, and the Similan and Surin marine parks close entirely.
The Gulf coast on the east (Koh Samui, Koh Phangan, Koh Tao) runs on a different schedule, generally good from around January to September and wettest from October to December.
Two things follow from this. First, there is usually good island weather somewhere in Thailand at any time of year, so let the season pick your coast. Second, and this is the big one: there are no direct ferries between the two coasts. To go from Samui to Phi Phi, you return to the mainland and cross over, usually a short flight (Samui to Phuket or Krabi is about an hour) or a longer bus. So unless you have two weeks or more, pick one coast and explore it properly rather than burning days crossing the country.
The two classic routes
The Andaman loop. The easiest and most scenic western chain runs Phuket to Koh Phi Phi to Krabi (Ao Nang and Railay) to Koh Lanta, with ferries connecting all of them in high season. Rough journey times are Phuket to Phi Phi around 2 hours, Krabi to Phi Phi around 1.5 hours, and Phi Phi to Koh Lanta around 1.5 hours. Phi Phi is spectacular but heavily touristed, so many people prefer to use it as a stop rather than a base and settle on the quieter beaches of Lanta or the limestone scenery at Railay. Far south, tiny Koh Lipe sits in a marine park with some of the clearest water in the country, reached by speedboat from Pak Bara in around 2 hours.
The Gulf triangle. The eastern circuit is tighter and easier: Koh Samui, Koh Phangan, and Koh Tao form a natural triangle, with crossings between them generally under two hours. Samui to Phangan can be as little as 20 to 30 minutes. Samui is the developed one with the airport and resorts, Phangan has the beaches and the Full Moon Party, and Koh Tao is the cheap diving base. Because Samui is the only one with an airport, most people fly in and out through it and day-trip or hop to the other two.
For something quieter, the eastern islands near Trat (Koh Chang, Koh Mak, Koh Kood) and Koh Samet are the closest to Bangkok and can be reached without flying.
How the ferries actually work
The network ranges from slick high-speed catamarans with assigned seats to older wooden boats, run by operators including Lomprayah, Seatran, Raja Ferry, Songserm, and Andaman Wave Master. A few things save you time and stress:
- Book through an aggregator. 12Go Asia is the most comprehensive platform and shows multiple operators with real availability. Ferryhopper and Klook also work, and many operators issue e-tickets you show on your phone.
- Book ahead in high season. Around mid-December to mid-January and near Full Moon Party dates, reserve popular Lomprayah and Seatran routes a week or two in advance.
- Arrive 45 to 60 minutes early for boarding, luggage, and seating.
- Do not plan tight flight connections. Delays happen even in good weather, so leave a buffer after the last ferry before any onward flight.
Where your signal actually disappears
Here is the part that matters for esimindexer readers, and the part generic ferry guides skip.
On the populated parts of the big islands (Phuket, Samui, Phangan, Tao, Phi Phi, Lanta) coverage is genuinely good, usually 4G and often 5G near the beaches and towns. The trouble starts in three specific situations.
On the water. Signal drops out mid-crossing on longer routes, especially the longer Andaman speedboat runs. Your ferry e-ticket, your onward transfer details, and your map need to work without a connection while you are between islands.
On the smaller and remote islands. Coverage thins fast once you leave the main tourist islands. Places like Koh Lipe, Koh Kood, and Koh Mak have basic coverage with real dead zones, particularly away from the main beaches, and the Similan and Surin islands have little to none. This is where the network your eSIM uses starts to matter: AIS has the widest rural and island coverage in Thailand, so an eSIM that routes to AIS is the safer pick for a trip built around remote islands. There is more on the AIS versus True difference in our full Thailand eSIM guide.
In a crowd. Coverage and capacity are not the same thing. During the Full Moon Party, Koh Phangan absorbs tens of thousands of people onto one beach, and the network gets so congested that data can crawl even where the signal bars look fine. Agree a meeting point and time with your group in advance rather than relying on being able to message on the night.
Your pre-departure connectivity checklist
Do these before you leave the mainland for each island group, while you still have a solid connection:
- Download offline Google Maps for each island and its surrounding waters. This alone solves most island connectivity problems.
- Screenshot or download your ferry e-tickets and QR codes so they open without data.
- Keep your TDAC arrival QR code saved offline too, since you fill that form in before you even land (details in the main Thailand guide).
- Choose an eSIM that includes AIS if your route features remote islands, and install it at home so it is live the moment you arrive.
- Download offline translation and any dive or ferry apps you plan to use before you are out of range.
The short version
- Pick one coast based on the season. Andaman (Phuket, Phi Phi, Krabi, Lipe) is best November to April. Gulf (Samui, Phangan, Tao) is best January to September.
- There are no ferries between the two coasts, so do not try to do both on a short trip.
- Book ferries through 12Go Asia, arrive an hour early, and leave a buffer before any onward flight.
- Coverage is strong on the big islands, patchy on remote ones, and drops out on the water. Download offline maps and save your tickets offline every time.
- For a remote-island itinerary, an AIS-based eSIM is the more reliable choice.
Ready to sort your data before you go? Compare Thailand eSIM plans on our Thailand page, and read the full Thailand eSIM guide for the complete network breakdown.
This guide is for general information only and does not constitute travel, legal, or telecoms advice. Ferry routes, schedules, prices, network coverage, and entry requirements change regularly and seasonally. Verify current details with ferry operators, your eSIM provider, and official Thai government sources before you travel.
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