There is no regular boat service for visitors to the island, and during the low season months of May-October boats may stop running altogether depending on the weather conditions. Thap Lamu Pier, in the Thai Muang district of Phang Nga province, is the nearest launching point to the Similans, with boat trips taking about 3 hours.
More adventurous travellers may try to hitch a ride with some of the local boats heading out there - just be sure to allow lots of time since there's no guarantee that there will be a ride back on any given day. Note that a park entry fee of 200 baht is charged.
Daytrips from Phuket and Khao Lak are also possible, with travel time of 45 minutes to 3 hours depending on the boat used. A popular way to go, especially for divers and game fishers, is by joining a liveaboard boat trip from Phuket, which usually run for 4 days. There are many Phuket-based liveaboard operations offering varying levels of luxury and facilities.