You want to paddle a kayak in a river?
or sail on a yacht in the Bay of Thailand, with your own captain?
On most any beach, you can rent a boat for an hour or a day with crew. A few places run booze cruises to the islands in the Winter.
On some beaches, you can rent jet ski's by the hour.
The daily island tours can be purchased at most hotels and guesthouses. Tickets are currently $15. This includes pick-up from your hotel between 7 and 8am, a small breakfast on-shore, a trip in a local fishing boat to one or more islands, lunch on an island, and snorkeling. Returning by 4pm or so. These can be on fishing boats holding 10 people, or bigger 2 story boats holding 50 people..
Sun Tours and Party Boat are both bigger boats and smoother rides. They cost $25 - $30 and you eat a buffet lunch on the boat. Great time!
You can book your speedboat online here
You can also check out the Scuba Diving page.
Hurricane Windsurfing - rents wind surfers on Otres Beach
Sunny Boat - Day tour of the Islands
CC Blue Sea Tours - Private Speed Boat and Daily Island Tour Boat.
Nautilus Island Tour - Private Speed Boat and a Daily Island Tour Boat
Chasing Tail Sport Fishing Charters - Inshore, offshore and estaury
Aqua Trip Cambodia - Crystal (see through) Kayaks on Otres Beach and island trips.
Golden Silver Gulf International Tourism Resort - Boat rentals to the island or just around the Gulf.
Captain Mike's - Big Game fishing trips and private island trips.
Also, check out the Cambodian Islands website
Many Cruises to SihanoukVille come from Saigon or Bangkok as part of a larger cruise tour. They usually stop here in the morning, and leave in the evening the same day.