Similan Islands

Nearly everyone dives the Similans from a boat that also sleeps them. Liveaboards leave the Khao Lak coast for two to four nights and settle into a rhythm of four dives a day, one before breakfast, two through the middle and one after dark, with the crossings made while divers eat or sleep. Speedboat day trips reach the same islands but lose an hour or more each way on top of the road transfer, so they fit two or three dives into a very long day. The park closes from mid-May to mid-October, so the season runs in one stretch from the autumn reopening to the following spring, and the calm December-to-March months fill up well in advance.

Which side of the chain you dive is decided on the morning by wind and current rather than by a fixed schedule. On the boulder sites the interest sits low down, where granite meets sand and the gaps between blocks form corridors you swim through rather than over; navigation is done off rock shapes because there is no continuous reef edge to follow. Water moves back and forth through those gaps even when the surface is flat, which is what makes the tighter passages awkward rather than the depth. The eastern slopes are shallower and easier, and take most of the check dives, night dives and camera work.

Few trips dive only the nine islands. Standard itineraries continue north to Koh Bon and Koh Tachai and, on longer trips, to Richelieu Rock, and that northern leg is where the current gets serious and the odds on big animals improve. Two boats both selling Similan trips can differ by several sites, so it is worth reading the route before booking. National park entry fees are collected on arrival and are usually charged on top of the boat price.

Boat life does most of the filtering. Entries are back-rolls from the dive deck or a tender, ascents often finish in blue water without a reference, and once aboard you dive whatever the schedule offers. A little drift experience goes a long way, and this works well as a first liveaboard because crossings are short and in-season seas are usually flat. Photographers get an unusual amount of structure to work with, and the east-side coral gives the macro-minded somewhere to go. Divers set on wrecks, dedicated muck sites or dependable big-animal encounters should treat those as things the trip may not deliver.