Just south of Koh Samui
Koh Tan and Koh Madsum sit off the south coast of Koh Samui. They are close enough for a half-day or a fuller boat day, depending on how you travel and how long you stay at each stop. This is a nearby-island outing, not a northern crossing like Tao or Phangan.
People go for quieter water, a second shoreline, and — on Madsum — the pigs that gave the island its nickname. The useful visit is a beach-and-snorkel loop, not a wildlife show.
Koh Tan
Koh Tan is the larger of the two in most visitors’ minds: a small inhabited island with local life, shoreline, and time in the water when conditions allow. It is a place to walk a little, swim if the sea is friendly, and see Samui from the other side of a short channel.
How much of the island you see depends on landing point, time ashore, and the boat’s plan. Do not expect a full village tour unless that is what you booked.
Koh Madsum, also called Pig Island
Koh Madsum is the smaller stop associated with free-roaming pigs on the sand. The pigs are part of the visit for many boats. They are not a performance, and they are not guaranteed to walk into the water on cue. Keep a little space, do not feed unless the people looking after the place that day say it is allowed, and do not treat the animals as a prop.
The beach and the short time in the water are still the point if the pigs are resting or elsewhere. A good Madsum stop works even when the photograph you saw online does not repeat.
Snorkeling and the beach
Snorkeling happens where the boat and the water allow it. Clarity, current, and how close you can stay to the sand change with the tide and the weather. Some days are easy swimming days. Some days are better as a look from the boat and a short walk.
This is not a deep-reef day in the Tao sense. Think of it as a south-island swim and shoreline day.
How you get there changes the day
Private longtail boats and speedboat trips both run in this direction. A longtail is often a smaller, more local-feeling boat. A speedboat is usually faster between points. Shared and private programs exist. Routes, stop time, and whether both islands are included belong to the product, not to a single island-pair rule.
Tide and weather matter more here than on a ring-road sightseeing day. A landing that is easy in the morning can be awkward later. Operators change the order or skip a stop when they need to.
Local fees and a light pack
Island or local fees may apply. Check the booked trip for what is included. Bring sun protection, water, and shoes that can handle a wet landing. Cash is useful for small local expenses.
If you want pigs-and-a-swim without a long crossing, this pair is the nearby option. If you want a full marine-park day, look at Ang Thong instead. If you want a northern snorkeling day, look at Tao and Nang Yuan.
SamuiToday can help you compare current south-island boat trips when you are ready. Decide first whether you want a private, unhurried boat or a faster shared day — then let the sea have the last word.