So you’re off on a dive trip and worried that you haven’t got a thing to wear – or, at least, nothing suitable for your destination. But how do you know what will be suitable? John Bantin explores the minefield that is scuba dive suit selection.
I sat at the aft deck of the Red Sea liveaboard, contemplating my fellow-passengers. Most were pulling from their bags skimpy 3mm wetsuits without full-length arms or legs. I looked at my rather chunky 7mm semi-dry and wondered if I had somehow got things very wrong.
I had not. For the second dive I opted to wear my hood as well. During the week’s trip, some of the other divers missed dives because they were getting just too cold.
We have long since left behind the days of The Deep, when Nick Nolte dived after Jacqueline Bisset in nothing more than his swimming kit, or Lloyd Bridges flexed his muscles in Sea Hunt. Today we routinely dive deeper and for much longer than the pioneers of scuba such as Hass and Cousteau. We expect our experiences to be as apparently comfortable as the film-makers of the ’60s would have us believe their heroes were.
I have never felt too hot during a dive, but I have been too cold. Different people have different tolerances to the heat loss that occurs when you are immersed in water. It’s a question of how much discomfort you are prepared to tolerate, and for how long and how deep you want to dive. Water might initially seem warm, but everyone gets cold eventually.
For British divers, the drysuit has become almost standard issue. The question is more how much insulation, in the form of an undergarment, to wear. However, in the late ’80s, I and many others used a 7mm semi-dry (with a 7mm jacket over it) extensively for diving off Britain’s south-west coast. The sea temperature of around 14°C proved quite bearable, though I always made sure I had a dry and warm suit to put on for the following dive.
Why the Right Dive Suit Matters
I never stop marvelling at those people who swim in the sea off the coast of Britain in summer wearing nothing but bathing costumes. Then again, members of the Moscow Swimming Club take a pride in getting into the river at Christmas. Not me, I’m afraid. I want to be comfortable, and when you get too cold, you stop thinking properly.
Each of us has made up our own minds about how we tackle the business of scuba dive suit selection, but when travelling to a new part of the world, how do you anticipate your scuba dive suit selection? We are subject to a great deal of misinformation on this. Much of what is put out in the press, national or specialist, seems to be the result of making phone calls and surfing the web rather than personal experience, and this received wisdom is then regurgitated by the experts in dive shops.
Some travel agents are just as bad. I went to Mexico’s Sea of Cortez for the first time and asked the British agent what suit I would need. She described it as “hotter than hell” out there and said a Lycra dive-skin was quite sufficient. I took one, together with a 3mm one-piece suit and a 7mm jacket. I ended up wearing all three and borrowing a hood, because, although the air was hot, the sea was icy. The presence of those elephant seals should have given me a clue!
Even one’s own experience cannot be relied on. While I remember it being very cold, the next time I went to that destination, I found that a close-fitting 5mm one-piece alone was sufficient.
How Cold Water Affects Divers
It’s not just a question of suit thickness. The first time I went to the Maldives, I took a thick 7mm long-john that allowed water to flush freely around my armpits. For the first 30 minutes of each dive I was fine, but then my air-consumption would suddenly go up as I used energy to keep warm. The blood supply at the arteries near the surface was being cooled.
Get cold and you need to metabolize more oxygen to make energy – you use more air. The next time I went I took a 5mm one-piece (complete with arms and legs) and it did the job.
It’s no surprise to find that you need a drysuit with a warm undersuit, hood and thick gloves for use in British Columbia or Newfoundland, but you might be surprised to find that your scuba dive suit selection should be similar when diving off the coast of Monterey, California. The west coast of the Americas is subject to cold currents, which keep at bay the warm, tropical water found on the other side of the Pacific.
The water temperature in the Galapagos islands and including the northern islands of Darwin and Wolf means that a full 7mm semi-dry suit and hood is almost essential. I used a 5mm one-piece with a 3mm under-vest and hood in the Cocos Islands, and I was using a lung-warming closed-circuit rebreather, too.
Cool Waters
Hoods are important, because you lose a lot of heat through your head, though they are often forgotten when looking at your scuba dive suit selection. They are also a little restricting, however, so there are times when I might trade mine off against a thicker, warmer suit to encase the rest of my body.
Ocean currents are usually cool. On a recent trip from the Seychelles to Aldabra I noted how the lightweight suits that were obviously adequate in the waters of the inner islands gave way to thicker suits and hoods as we found ourselves exposed to the ocean flow.
In the same way, the water inside the atolls of the Maldives will always be a lot warmer than that on the outer reefs with the big fish.
In South-east Asia, if you stay within the warm inner seas a thin one-piece suit might be OK, but if you are diving in Indonesia, for example, stay out of the Indian Ocean proper if equipped with nothing more.
Similarly, the Canary Islands lie on the same latitude as the Sahara desert, but the Atlantic Ocean surrounding them can be quite chilling for the unprepared.
Regional Scuba Dive Suit Selection Examples
The Caribbean is warm. It doesn’t really have a cold season, although locals might think otherwise. The suit that works in the summer there, a 3mm or 5mm one-piece, works equally well in the winter season too. The Bahamas are more subject to the will of the Atlantic but it stays pretty warm there too, unlike Bermuda, way out in the ocean, where a thicker suit is more appropriate.
The Mediterranean might get as warm as a bath at the surface during the summer, but waiting below the thermocline is a body of water that stays at a steady 14° – 17°C all year round.
The sort of suit you need will depend on where, when and how deep you go affects the sort of suit you need. I think a drysuit is essential outside the May-to-October period.
Both South Africa and Australia are very big places. The sort of suit you need varies from drysuit to 3mm one-piece, depending on where and when you are diving.
So how do you find out whether your scuba dive suit selection is right for where you’re going?
It’s a mistake to look at the map and decide that two places have the same water temperature simply because they share the same latitude. After all, you don’t expect that of London and Moscow.
Friends who have been to destinations will often give you the wrong steer rather than admit that they got it wrong. The best idea is to find out what the local dive-guide is using.
Layering Dive Suits for Flexibility
Another good solution when it comes to scuba dive suit selection is to take a suit that can be built up in layers. You could choose a 3mm or 5mm one-piece as a base and have a jacket to go over it (or a vest to wear under it) and a separate hood. You can always peel one layer off if you really do find it too hot or restricting. Wear a suit that fits properly and is neither a trauma to get on nor so loose and full of water that you swim within it.
In the UK you are most likely to wear a drysuit, but even here there will be a choice of insulating undergarments. Their effect is to fill the cavity between you and the outer wall of the suit so that a layer of insulating air can be maintained, rather than using a thin layer of water as in a wetsuit or semi-dry.
Materials that do not bridge the air space and thereby conduct heat away from you to the outer membrane are used. Thinsulate and Flektalon are two proprietary brands of insulating material, while other suits use assorted microfibres to fill the space. The outer layer of the undersuit is normally some type of hard-wearing man-made fiber, while the inner layer is usually a material with a high wicking property that will soak up cooling sweat and draw it away from your skin.
Neoprene drysuits use the outer shell as an insulating layer but they are still more often than not used with some sort of lightweight undersuit.
Crushed neoprene is just another material, a very tough one, used for some membrane suits. Compressed neoprene allows you to hedge your bets with scuba dive suit selection and split the task of insulating your body between the outer shell and an inner lightweight undersuit.
Wearing too much lead means filling the suit with more air than would otherwise be needed. Under water it tends to form a bubble at the upper back, distorting the suit by pulling it tighter round the lower legs and actually making you colder!
Whatever your scuba dive suit selection, it’s important that the suit fits you properly. A suit that’s a struggle to get on in a hot and sweaty tropical destination can confuse you into not wearing a suit at all. A membrane drysuit that is too big can be very resistant when it comes to swimming through the water, and unnecessary folds of material can cause sore spots where it rubs. If you are an unusual size, take the time out to get a suit made to measure.
Coming Up Short
You will have noticed that I have not mentioned the 3mm shortie as a sensible scuba dive suit selection. This is because, even in the warmest waters, you will find you need some protection from stinging hydroids and plankton, and climbing the ladder of the boat can often result in bruising on unprotected limbs.
In my opinion you can keep those skimpy suits for surfing and pool-training. Keep warm and you’ll find you can go a whole hour without taking a pee, in exactly the same way you do when you’re not diving.
Why Cold Makes You Want To Pee
Who’s warmer? A diver in a Lycra suit diving in water at 28°C, or a diver in a drysuit with a good undersuit, diving in water at 12°C?
Water conducts heat about 20 times more efficiently than air. Get air in your central-heating system and you’ll soon notice the difference. So people immersed in water that is colder than their skin temperature soon get chilly. We use insulation to try to retain as much body heat as we can, but heat-loss is a universal problem for divers, regardless of the ambient water temperature. People get cold diving in the warmest conditions. Unless the water temperature is more than 32°C, you will lose heat.
The human body core must maintain a constant temperature to work efficiently. The response to a drop in core temperature is complicated. The extremities are starved of blood, as the vessels narrow and shift it to the core. This is interpreted by the brain as over-hydration, and in response it shuts down production of the anti-diuretic hormones, causing in the diver a desire to urinate.
Does this sound familiar? If you find you need to pee in your suit during a dive, perhaps your scuba dive suit selection needs some work, and you need to look at something warmer.
There is significant heat loss with urination, not to mention the risk of dehydration and important consequences regarding decompression illness. Shivering occurs at first only if the diver is not swimming vigorously, so we suppress it by heavy activity.
If you are on land, in air, you can try to keep warm by exercise. Even on the coldest day you can work out until you perspire. Under water, alas, heavy exercise simply masks what’s really happening. The water efficiently drains away any heat produced in this way, and does so faster than you can produce it, so you lose more heat than if you simply stay still and shiver.
The effects of breathing nitrogen under pressure (narcosis) can inhibit shivering too. How many times have you heard trainee divers in tropical places, probably learning to dive without the aid of a suit, ask: “Why does diving make me so tired?” Heat loss can be so slow and gradual that you don’t notice it. The net result is a cold, tired diver and a reduced bottom time.
Have you noticed that on a long series of dives, the sort you might make during the course of a stay on a liveaboard dive boat, you get more tired towards the end of the trip? The effect of heat loss is cumulative, too. So the first thing we have to do is insulate the key areas of our body from the conductive effect of the water.
Frequently Asked Questions
What type of wetsuit do I need for scuba diving?
The right wetsuit depends on water temperature, dive depth, and personal tolerance to cold. Common options range from 3mm tropical suits to 7mm semi-dry suits.
When should I wear a drysuit instead of a wetsuit?
A drysuit is ideal for cold water diving (below ~15°C), where insulation layers can be adjusted to keep you warm and extend dive times.
Do I need a hood when scuba diving?
Yes. A hood helps prevent significant heat loss from the head, especially in cooler waters, improving comfort and air consumption.
Why do divers get cold even in warm water?
Water conducts heat away from the body 20x faster than air, so even tropical dives can cause gradual heat loss and diver fatigue.
What’s the best way to prepare for different dive destinations?
Check local dive guides’ recommendations, pack layerable suits (e.g., 3mm with an over-jacket), and remember that ocean currents can make water colder than expected.
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