Deep Diving

Most divers who complete their Advanced Open Water course have been to 30 metres — the target depth for the deep specialty dive in that course. The Deep Diving specialty takes the next step, extending that limit to 40 metres and covering the planning, skills, and awareness needed to dive safely at that depth.

Forty metres is the limit of recreational diving. Below that you’re into technical diving territory with decompression obligations and more complex gas management. At 40 metres the recreational diver has access to everything the sport offers — which around Koh Tao means the bottom of Chumphon Pinnacle, the deeper sections of Southwest Pinnacle, and a handful of other sites that simply aren’t accessible at shallower depths.

The changes you notice at depth are real and worth understanding. Light behaves differently — colours in the red spectrum disappear first, so the reef takes on a blue-green cast that looks nothing like the same site at 10 metres. No-decompression limits shorten significantly, so bottom time becomes a more active consideration.

Nitrogen narcosis — a mild, reversible effect of nitrogen at pressure that some divers compare to a glass of wine — is more pronounced at 30–40 metres than in shallower water. The course covers all of these in theory and gives you the experience of managing them in practice.

The two dives go progressively deeper — the first to around 30 metres to establish comfort and practice the skills, the second pushing to 40 metres at a site with something worth seeing at that depth. Chumphon Pinnacle is the most common choice — the deeper sections of the pinnacle have a different character from the shallower reef and are worth the bottom time.