Similan Islands · Thailand · Reef · Pinnacle
Boulder City
Big granite blocks with reef sharks and Napoleon wrasse
Area photo: Reinhard Link · CC BY-SA 2.0
Boulder City is a field of large granite boulders, cliffs and rocks standing on a sand bottom off Ko Payan, Similan Island No. 3. The usual profile runs 10 to 25 m with the site's quoted maximum at 40 m, and the size of the rock is what shelters the fish: reef sharks, Napoleon wrasse and bumphead parrotfish work the gaps while the open sides of the site pull in current.
Where it is and how deep
8.5099° N, 97.6703° EPublished position for this site.
The dive
The site is what the name says: large granite boulders, cliffs and rocks sitting on a sand bottom off Ko Payan, Similan Island No. 3. The usual range is 10 to 25 m with the site's quoted maximum at 40 m, and visibility of 20 to 30 m means the shape of the next block is generally readable before you leave the one you are on, which is how divers navigate a site with no continuous reef edge.
Current is usually gentle here and can turn quite strong, and the site is open and unprotected with nothing to break it. The way it is dived reflects that: stay on the calm side of the boulders, cross the gaps between them in short legs, and make the descent and the ascent on the anchor chain rather than in open water.
The rock holds the fish that need its shelter. Reef sharks and leopard sharks work the sand, Napoleon wrasse cruise the tops of the blocks, and there are large bumphead parrotfish and schooling barracuda through the gaps. Manta rays and whale sharks are both possible at this site, though neither is anything to plan a dive around.
Marine life and season
- Reef sharks
- Napoleon wrasse
- Barracuda
- Manta rays
- Whale sharks
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Prime | Prime | Prime | Prime | Fair | Off-season | Off-season | Off-season | Off-season | Fair | Good | Prime |
Season follows Similan Islands: The park is closed by law from mid-May to mid-October; December to April is the calm high season.
Know before you go
- The site is open and unprotected and current turns strong in places; the standing advice is to keep to the calm side of the boulders and cross the gaps in short legs.
- Descent and ascent are made on the anchor chain, since in current there is no other reference between the boulder field and the surface.
Dive videos
Dive #1: Similan islands - boulder city dive site · Raffaele Guidi on YouTube
Questions divers ask
How deep is Boulder City?+
The typical range is 10 to 25 m among the boulders, with the site's quoted maximum at 40 m. The advanced rating comes more from the current than from the depth.
What can you see at Boulder City?+
Reef sharks and leopard sharks over the sand, Napoleon wrasse and large bumphead parrotfish around the boulders, and schooling barracuda. Manta rays and whale sharks are both recorded here but are a matter of luck.
Sources
- Boulder City dive site — Divezone
- Diving in Thailand — Wikivoyage
- Similan Islands Dive Sites — Dive The World
In The Logbook
- Where to see reef sharks on your first divesBig animals · 14 min read
- Where to dive with whale sharks, month by monthBig animals · 16 min read
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Similar dives elsewhere
A current-swept pinnacle from 30 m to within 5 m of the surface
Sloping reef and island-side pinnacles, dived off a mooring
Swim-throughs and pinnacles from 10 metres, diveable year-round.
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Leopard sharks on the sand under three pinnacles