This post was submitted by Luca Malaguti. Luca dove with a 3 mm suit in the cold water of the Pacific for the longest time. In this article he shares some tricks to stay warm.
The Canadian Pacific Northwest is a stunning place for scuba diving, freediving or snorkeling. It offers some of the cleanest waters in the world, fantastic underwater landscapes and unbelievable marine wildlife. The only issue for many people that wish to take part in these activities around Vancouver, the Gulf Islands or Victoria, is that for most of the year the water is quite cold.In the summertime, the Howe Sound can have surface water temperatures that range between 14 to 20 degrees Celsius. However, it’s always cold below the thermocline.
Staying warm while freediving is an art, especially in colder waters. During a normal 2-hour dive session you can easily lose more than 700 kcal just on heat loss, and if you lose heat too fast, your dive session will be cut short. Here I’ll share some surprising information about the performance of your wetsuit, and what you can do to stay warm in the water.
High heat loss despite a wetsuit
Conductive heat loss is something we can calculate. I am not going to try to bore you too much with the details, so here is the condensed story.
How much heat you lose through conductive heat transfer depends on four things. 1) The temperature difference of your skin and the water around you, 2) the thermal conductivity of your wetsuit, 3) the thickness of your wetsuit, and 4) the surface area of your body.
Wetsuits contain up to 94% nitrogen bubbles. The nitrogen is what prevents heat loss. The neoprene itself is actually quite conductive. Nitrogen compresses just like air, so at depth the suit becomes thinner and the overall heat conductivity increases.
Conductive heat transfer does not include water sloshing through your wetsuit. It is simply the amount of heat you lose if you were to be still, in still water.
Here are some interesting results based on conductive heat transfer alone:
A diver in a 3 mm suit and 25ºC (77ºF) water loses more heat than a diver in an 8 mm suit in 8ºC (46ºF) water
Heat loss at 20m is 4 – 5 times as high as at the surface
Heat loss at 40m is 7 – 8 times as high as at the surface
You will commonly lose at least 500 kcal of energy during a 2 hour dive session
At 40m depth, you can lose as much heat as a medium sized space heater generates (3000W), depending on the thickness of your wetsuit
Planning your dives so you stay warm
When I initially calculated the difference in heat loss between cold and warm water divers, I thought I made a mistake. How on earth can a diver in 25ºC water with a 3 mm lose as much heat as a diver in 8ºC water with an 8 mm suit? I know from experience that I can spend all day in warm water, and only a couple of hours in cold water.
The answer is that conductive heat transfer is not the full story. If the sun is directly above you (midday on the equator), it will supply the earth surface with >1000 W/m2 of heat. Those 25ºC waters we talked about earlier get much more direct sunlight. In a 3mm suit you only lose ~300 W at the surface, so the sun is instrumental in keeping you warm.
The sunlight hits regions farther from the equator such as Canada and New Zealand at an angle (see also: solar irradiance). Because of that, the sun supplies much less heat to the freedivers that call these waters home. In these regions, if you want to stay warm you need to plan your dives when the sun is high. That is not difficult in the summer, but in spring and fall you should try to dive in the afternoon, preferably on days without cloud cover. In the winter… may Poseidon be with you.
Wind and evaporation
Part of your body is above the surface during your breathe up. If the apparent air temperature (apparent air temperature takes into account wind chill) is lower than the water temperature, this will cause you to lose heat faster. The increase in heat loss can be as much as 10%, if you dive during a 0ºC day.
More important is the effect of evaporation. When you are above the surface, the water on your suit will evaporate. During evaporation, liquid water extracts heat from its surroundings. Unfortunately its surroundings are you, or rather, your suit. Evaporating water costs a lot of energy, and how cold you become during a dive might be directly proportional to the rate of evaporation. Wind will increase the rate of evaporation, and so does heat. If you have a smooth skin suit, there will be less water to evaporate than if you have a lined suit.
Diving style and getting in and out of your wetsuit
Diving style is another big part of staying warm. Our muscles are very inefficient, and about 80% of the energy we use is lost as heat. A more active diving style will keep you warm for longer. You will of course sacrifice some performance.
Lastly, what you do before you get in the water will also affect how warm you will be. Make sure to store your wetsuit in a warm(ish) place before a dive session, and try to stay warm while you change. I know one diver that changes in a bathing robe, and transports his wetsuit in a cooler with jugs of hot water. The jugs of hot water do excellent service as a post-dive shower.
Try to dive when the sun is high if you are far from the equator
Try to dive in low winds
Check the weather forecast and wear a (thicker) suit if there is cloud cover
Adjust your diving style to suit the water temperature. Long line diving sessions, deep targets and hangs are for the summertime
Stay horizontal at the surface, to allow your entire body to be heated by the sun (if there is some)
Try to stay as warm as you can before you get into the water
Diving with a smooth skin suit is warmer than diving with a lined suit of the same thickness
The first wetsuit I ever used for freediving was a surfing wetsuit. The finest cheapest I could find. It came from Decathlon in France, and had a 5.5/4.5 mm longjohn and a 5.5/4.5 mm jacket. Combined I had 11 mm of neoprene on the core, and 4.5 mm of neoprene on my limbs. That wetsuit lasted forever. It was also about as flexible as a wooden board, and very heavy.
My next wetsuit was an actual freediving wetsuit, a 3mm speardiver from the freedive store. I still have it, although the original 3 mm neoprene now is about 1.5 – 2 mm thick. The wet suit has an unlined inside, commonly referred to as ‘open cell’, meaning that there is no lining on the rubber. Rubber against skin. That whole story of having a thin layer of water to help you stay warm? Total nonsense. If you have less water and/or water flow in your suit you are going to stay much warmer. Compared to my surf suit, diving felt like a trip to heaven and back. I then got a suit from Oceanos in Greece. Not the best suit I ever bought. It was a cheap custom suit, but the fit was not perfect. After a year of diving, the original 5 mm has compressed to about 3 mm.
I now dive with a suit from Azure Passion (review here). It is 8 mm thick, and so far (after 6 months of diving) it is still 8 mm. I take a lot more care with this suit, because it feels like a second skin, and, I really should stop buying a new suit every 8-12 months.
Simple tricks to make your freediving wetsuit last
Make sure the neoprene does not compress
Store your suit on a shelf without folds (My pants are folded once, and of my top the sleeves are folded at the shoulders). Do not put anything on your suit. I repeat. Do not put anything on your suit. Not your divelight, not your mask, and not your diving weights. Especially not your diving weights. If neoprene compresses it will lose its insulation. Not a big deal if you dive with a 1.5 mm in the tropics, big deal if you dive in BC in water that can be below 5 °C.
I stuffed my first suits into the smallest bag I could stuff them into. It was handy, especially when I lived in my van for 8 months. But it definitely was not good for the neoprene. Now I use a huge bag for my suits so that they have plenty of space. The quality of the neoprene is another factor. Yamomoto and Heiwa neoprene are currently the best available to my knowledge.
Make sure the neoprene does not stretch
You can keep a wetsuit on a hanger but some neoprenes tend to stretch if you do this.. This doesn’t happen instantly but it sure does happen. If it does you have created space for water to slosh around and this will keep you cold. This is part of the reason I keep mine lying on a shelf.
Take care of the small nicks and cuts as soon as you can
If you have an unlined wetsuit, don’t breathe at it! Chances are you’ll create a hole. These suits are fragile. Even a fingernail can create a small cut. That small cut will turn into a tear very soon. Keep neoprene cement in your diving bag (put 2 ziplocks around it in case it leaks) so that you can mend your suit on the go. Make sure you can put your suit on and off without having your fingertips against the rubber.