Koh Tao Open Water Course Lessons, Part 4 | Dive Environment

Previously in this series of mini lessons from the Koh Tao PADI Open Water course we’ve looked at the following topics:

Now in part 4 of Simple Life Divers’ micro lessons we’ll take a look at the environment which we’ll be diving in, and discuss the factors which affect our diving around Koh Tao. Here we go….

PADI Open Water Koh Tao Lesson 4: Introduction

When you look at a swimming pool, conditions are very controlled – usually the water is flat, still & clear, the bottom composition is consistent, and the temperature is normally kept steady.

But out in the open ocean all those factors are beyond our control, and will affect our diving delivering different experiences from day to day. Let’s take a look at some of the biggest influences and how they affect our Koh Tao open water dives:

1. Water Temperature

Since you lose heat much faster in water than air, it’s important that you wear the right kind of exposure suit to keep you comfortable whilst scuba diving. However diving around tropical Koh Tao we’re very comfortable – the water is steady at around 29C, and very rarely drops below 27C so it’s a very comfortable temperature for scuba diving. Most people are sufficient in a shorty wetsuit, or even a pair of shorts and a rash vest.

But there’s another issue with water temperature which isn’t so obvious – ’Thermoclines’.

Image: A rough sketch of the thermocline diving Koh Tao‘s famous Chumphon Pinnacles dive site

In the ocean water often sits in layers. We sometimes find a sun-heated layer of warmer water near the surface, covering a cooler layer of water which rests on the seabed. Very little mixing takes place between these layers. Descending down from the warmer layer into the deeper cooler layer, you sometimes feel the chill, as the water temperature drops by a couple of degrees.

Even more interestingly, light can be refracted as it travels through the boundary between the layers, causing a visual distortion. And even more importantly, our experience diving in Koh Tao is that the top warmer layer usually has excellent visibility, often crystal clear. Yet when you descend down into the cooler layer, visibility can drop to zero, so you can barely see your hand in front of your face. Sitting above that layer, it’s kind of like being stood on a mountain, looking out over a misty valley.

So how deep is the thermocline diving in Koh Tao? This varies from day to day, but a good average might be 24 – 30M depth. Probably the best site to experience the view of a thermocline is Koh Tao’s famous Chumphon Pinnacles dive site. A giant granite pinnacle rises up from the seabed at 30M, to within about 14M of the surface. The bulk of the pinnacle is surrounded by the clear, warm upper layer. Yet around the base of the pinnacles, and on the sand sloping downwards away from the dive site, you’ll be able to see the ‘misty’ cooler bottom layer below the thermocline.

What makes it even more fun, is that on some occasions you’ll get to see one of the large sharks swimming up out of the zero visibility cooler layer to check out what’s going on – fantastic!

2. Underwater Visibility

We’ve touched a bit on this in the last factor. Visibility means the distance which you’re able to see in a horizontal direction underwater, and makes a massive difference to your diving experience.

Although it can sometimes be quite amusing swimming around in zero visibility murk, generally speaking most divers prefer to dive in good visibility as you’ll obviously be able to see much more and navigate around the dive site more easily by picking out landmarks. Visibility changes from day to day, depending on things like:

Wind, Waves & Water Movement: Big waves stir up the seabed, distributing fine sand or silt throughout the water which can cause a drop in visibility

Rain: Not so important, but if you’re diving near a large landmass, heavy rain can cause run off from the land which washes sediment into the ocean, again causing a drop in visibility.

Bottom Composition: If the seabed is made from hard substances like rock, coarse sand or a continuous coral reef, there’s very little material which can be disturbed to cause a drop in visibility, so you’re more likely to have good diving conditions. But diving over a fine sand or silt covered bottom, you’ll want to be really careful fining to make sure you don’t kick up a mess and disrupt visibility.

Image: Navigating around the White Rock dive site west of Koh Tao, much of the bottom is made from hard granite rock boulders and hard corals

So how about the visibility scuba diving in Koh Tao? Again we’re very lucky – located in the Gulf of Thailand, Koh Tao is relatively sheltered so year round we get little rain, wind or waves. On a good day visibility above the thermocline can be upwards of 30M, which to a diver appears like crystal clear blue water.

The ultimate best conditions are when the sea is dead flat, it’s hot and sunny and there is little water movement – that’s when we’ll be hitting maximum visibility.

Image: That’s how we like it – ocean as flat as a pond as we’re scuba diving Koh Tao in the Gulf of Thailand

3. Currents

Oceanic currents can be very strong, so it’s important that we take the current into consideration when planning our dives.

Ignoring the effects of rocks and islands, in the Gulf of Thailand the current are easy to explain. As the tide is rising, water is moving up the Gulf, towards Bangkok in a northerly direction. Then as the tide drops, water moves south exiting the Gulf of Thailand into the South China Sea.

The best time for us to dive is when the tide is slack – that is neither coming in nor going out so there is no water movement. Yet it can sometimes be fun to plan to dive when the current is running – rather than attempting to swim against the current we can plan to make a one way drift dive, dropping in at one spot and exiting the water elsewhere. An especially good Koh Tao dive site for this is Shark Island, off the south tip of Koh Tao.

Generally speaking though, diving Koh Tao the currents are pretty mild, and many of our dive sites are tucked into bays which shelter us from the current. This means we get to enjoy nice, relaxed dives, and can conserve our air supply and enjoy long bottom times!

Image: PADI Instructor ‘Woody’ avoids exerting energy whilst swimming in current by using a DPV (dive propulsion vehicle)

That wraps up our quick look at some of the factors affecting our dives, and relating those to the Koh Tao diving environment. More to come in part 5 of our series of lessons from the Koh Tao PADI Open Water course – check back again soon.