Cold weather diving

[dutchman]

So what do you do to keep warm during a surface interval?
Is there some technique or method you use when it is 37 degrees at the surface?

[MSilvia]

I leave my drysuit on... that seems to help quite a bit. When I was diving wet though, I'd make sure to get out of my wetsuit to mitigate evaporative cooling, and "prime" my suit with a thermos full of warm water before putting it back on. I'd also usually drink a few cups of hot tea, both to warm me up now, and so that I'd be able to "re-warm" myslef during the dive, if you take my meaning.

I wrote an article about cold-water diving for a local shop last year, so Ill provide a link to it and repost the content.

The article is about half way down this page. It's also reproduced below.

[MSilvia]

New England is famous for the changes of the seasons, and for most local divers the first signs of cold weather mean the end of diving and the start of a long, dry, winter. Even those folks who bravely splash right past Labor Day and take advantage of the relatively warm waters of early autumn have mostly hung up their fins before the first snow falls. For those of us who dive year round however, the end of what’s generally accepted as “dive season” means a whole new set of dive opportunities, and the fun and satisfaction of building a set of skills that allow us to safely and comfortably dive locally in all but the worst cold.

Hey, this is New England. Sometimes it’s cold here whether you dive or not, and just like on land how comfortable you are when it’s cold outside depends on how prepared you are to keep yourself warm. Remember, the majority of divers in the world never dive in water colder than 70 degrees. If you wouldn’t cancel a ski trip due to cold weather, there’s no reason you can’t have every bit as much fun on a winter dive. All it takes is some nice warm exposure protection, a little know-how, and some simple preparation.

If you already dive locally, the odds are good that you already have a decent cold water suit. For those who dive in a drysuit, applying some simple stay-warm strategies can give you the ability to dive locally all year long with no trouble. So long as you are wearing a warm enough undergarment (and dry enough suit!), you should be able to stay comfortable in even the coldest water. Even if you dive with a wetsuit though, you can still take advantage of many of the same strategies and enjoy diving for most of the year.

The Benefits
Okay, so it’s possible to dive in New England in the winter. It’s also possible to spend the winter wrapped up in a blanket in front of a warm fire with a cup of cocoa, so why should anyone in their right mind deliberately jump in the ocean when even the fish think it’s too cold to stick around?

While it’s true that there isn’t as much marine life around when the water turns cold, this has its positive side. Sure, there aren’t many lobsters running around in January, and most of the fish have headed for more temperate waters, but there are a lot of sea creatures you may be pleased to see have gone. They’re called plankton, and you may recognize them as the tiny, sometimes microscopic, creatures that float around everywhere for most of the year. They don’t like the cold much, and when they’re gone, the visibility can increase dramatically! Not only does a reduction in animal life not mean there’s “nothing to see”, but it can actually mean that you can see quite a bit more when the conditions are favorable. While there aren’t as many charter boats operating in the winter months, there are those that do, and if you charter a boat (especially one with a heated cabin!) for a wreck dive when the winter conditions are favorable, the unusually clear water can be a real treat.

The end of dive season also conveniently corresponds with the end of tourist season, and that means something that should be music to the ears of shore divers: Easy Parking. The lack of crowds coupled with the lifting of parking restrictions during the off-season means that even on a Saturday afternoon at the most popular sites, it’s often possible to pull right up and take your pick of the best parking spots without fear of being ticketed or towed. With the transient nature of New England weather, that can sometimes mean getting prime dive parking on a very nice day. Just recently the air temperature was 67 degrees in Boston, beautiful weather for a dive in December!

Staying Warm
Winter diving can be great fun, but with the cold comes additional safety concerns that must be taken seriously in order to stay safe and comfortable. The primary concern of cold water divers should be avoiding hypothermia, a medical term meaning reduced body temperature. Shivering is usually the first sign of hypothermia, and a shivering diver should immediately abort the dive as a safety precaution. Other signs may include loss of coordination, weakness, and poor decision making. As hypothermia worsens, a victim will usually stop shivering and feel suddenly warmer as a result of blood rushing to the skin. This is a dangerous sign, as the body’s core temperature can begin dropping rapidly at this point, and may lead to loss of consciousness and death.
Once a diver becomes cold, it’s nearly impossible to warm back up underwater, so the first and most important thing you can do to stay comfortable when diving in cold weather is to avoid losing the heat you already have. This means retaining body heat not only during, but also before the dive, as body heat lost while preparing to dive is often a major contributor to the onset of hypothermia.
Again, the whole point is to have fun, and it’s no fun to get cold. Wearing proper exposure protection is the key to enjoying cold water diving.

Warm and Wet
There is little question that the most popular choice of exposure protection with divers worldwide is the wetsuit, and it’s no different here in New England. If it fits well, is sufficiently thick, and properly designed, a wetsuit can keep a diver warm in surprisingly cold water. A 7mm thick suit is generally advised for wetsuit diving in our area, and while in the recent past a 2-piece “farmer john and jacket” suit would be the best wetsuit option for diving in the colder months, there are some new innovations in insulation and suit lining that have created viable options for single piece suits as well. Regardless of which type of wetsuit you choose, there are some important things you should know if you plan to dive one when it’s cold outside.

The first, and perhaps most important of these things is that you need to protect yourself from evaporation during the surface interval. As you’ll remember, your wet suit works by allowing a thin layer of water to be warmed up by your body. While this can keep you relatively comfortable for some time underwater, it is not designed to have the same effect on land. Once you leave the water, the wet exterior of your suit will rapidly rob you of body heat through convective cooling. After your exit from a winter wetsuit dive, it’s important to change into warm dry clothes as soon as is possible, ideally (though not necessarily) in a heated location like a boat cabin. If a repetitive dive is planned, at the very least strip off the top of the suit and wear a warm jacket or pullover during the surface interval to protect your body core from heat loss.

Comfort in the water is important too, and the trickle of cold water into your suit when you begin your dive can be quite an unpleasant surprise. This problem can be dealt with by “priming” your suit with warm water. Bring a thermos full of very warm (not hot!) water with you, and before you make your entry, pour some of that water into the suit. By using this strategy, the layer of water against your skin will already be at a comfortable temperature, and you will not waste valuable heat energy in warming it up. It’ll also prevent the suit from filling with cold water when you get in, so the transition into the underwater world will be a much more comfortable one.

Priming is also an especially welcome comfort-enhancer on repetitive dives. When you go to put on that wetsuit you peeled off an hour ago, remember that it’s damp and has been sitting in cold air. Slipping back into it after it’s had a nice warm dousing from your thermos will be a much more inviting experience. I’ve been on boat dives where the wetsuit divers with no warm water opted out of the second dive for not wanting to change out of their warm clothes into icy wetsuits. I don’t blame them a bit. When repetitive diving in cold water, it’s a good idea to give yourself plenty of time to warm up during the surface interval. If you can’t start a second dive warm, you may want to consider not starting it at all.

Remember though that it’s a big cold ocean, and no matter how well your suit fits and how warm the water you primed it with was, you’ll cool as you dive. Don’t be surprised to find that on cold water dives it will probably be temperature and not your pressure gauge or NDL that will determine when it’s time to turn a dive. When you start to feel cold, it’s time to head back. There are some divers who will extend their comfortable time on wetsuit dives by staying well hydrated so that they can “re-prime” their suit when their skin feels cold and bladder feels full, but I’ll leave such delicate matters to your discretion.

Extremities
Since heat loss can occur rapidly from the head, hands, and feet, your extremities must not be neglected. It of course goes without saying that a good hood is a necessity for diving in New England waters, as is a warm pair of wetsuit boots, so you probably have those covered already. You probably have a pair of gloves too, but for cold water you may want to consider purchasing a pair of “3 finger” mitts instead. Unlike conventional gloves, diving mitts allow several of your fingers to be next to each other, where they can share warmth. It makes a bigger difference than you might guess, and since your index finger will still be independent of the others you won’t sacrifice much of your ability to grasp and manipulate things by wearing them.

Your hands are likely to be one of the places you notice the cold first, and if they get cold enough that numbness sets in, the loss of dexterity while diving can add danger to the simple unpleasantness of being cold. You want to make sure you have the ability to work your inflator and to get yourself out of your gear post-dive, so keeping your hands as warm as possible is important.

Diving Dry
For those who want the utmost in comfort when diving in cold water, there’s nothing quite like staying warm and dry while you do it, and it’s for this reason that many avid cold water divers choose to dive in a drysuit. It’s also worth noting that as you dive deeper, a wetsuit will lose more and more of its ability to insulate, but a drysuit will not. This is because a drysuit diver is able to add gas to the suit as needed to maintain it’s volume, and to keep loft (also known as fluffiness) in the insulating undergarment that keeps drysuit divers warm. If well maintained, a drysuit can keep a diver warm enough for diving in extreme conditions like under the ice! Scientific research divers even use these suits to explore beneath the polar ice caps!

Aside from keeping a diver dry though, there are several other advantages drysuit divers have in cold water. One of these is the option of using dry gloves, which protect the diver from the aforementioned problems related to cold hands, and another is the ability to use argon as an inflation gas. Argon does not conduct heat as well as air, so it’s a more efficient insulator against losing body heat to the cold seawater. For this reason, some dry divers will get a small (6 cubic foot or so) scuba tank specifically so they can fill it with argon and use it solely to inflate their suit.

Drysuit diving can present a whole new set of challenges for a diver though, and it takes some practice to get used to using one. A drysuit class can be helpful in ironing out some of the initial difficulties that come with managing a suit that has a big gas bubble in it. If diving dry is something that interests you, talk to your local dive shop about it!

Warm Clothes
Lets not forget it’ll still be cold when the dive is over, and it’s as important to have warm clothes to change into as it is to stay warm during the dive. It may be even more so. Be sure that in addition to street clothes and a towel, you pack a hat, gloves, dry socks, and weatherproof coat. You may want to consider purchasing a waterproof dry bag to keep your clothes in, as things sometimes get wet near dive gear, and dry clothes will keep you much more comfortable. Adding a chemical heat pad to your bag before the dive can keep those clothes nice and warm for you, and having an active heat source for your hands can be a great help after a cold dive too.

Since I mentioned the heat pad though, I should mention that if you’re a drysuit diver with heat pads, it could be tempting to slip one (or several) into the suit before you dive. Do so with caution! Most readily available pads react with oxygen, and are designed to work in typical atmospheric conditions. I’ve heard several stories about divers who used these pads in their drysuits while diving with oxygen-enriched nitrox, which they were also using to inflate their suits. In a 36% oxygen environment instead of the usual 21% found in air, the pads got VERY hot, and the divers had to be treated for some fairly serious burns. It’s worth keeping in mind, if only as a cautionary tale you can tell others.

Regulators
About Regulators
Aside from the concerns associated with keeping yourself warm, another major consideration when cold water diving is the prevention of regulator free-flow. Free-flow is what happens when ice crystal form inside the first or second stage regulator, jamming it open and causing gas to rush out uncontrollably. Obviously, this can lead to the rapid depletion of your available breathing gas, and is not at all desirable. It happens because of the cooling effect of rapid depressurization of the air in your tank.

As all divers know, the air in a scuba tank is highly pressurized. Your regulators, of course, are responsible for reducing this pressure to a degree that makes it usable, and depressurization causes cooling. You may have seen this effect yourself if you’ve ever drained a scuba tank, grill propane tank, or other pressurized container quickly and noticed frost forming on the container. The opposite is also true, as anyone who has ever gotten a rapid “hot” tank fill will tell you.

The first stage regulator reduces the pressure from that in your tank significantly, and as always, a reduction in pressure causes cooling. In fresh water that’s already close to the freezing point, this further cooling can cause ice to form on and around the first stage, and that ice can interfere with the proper function of the regulator. This can be especially problematic if the air in your tank is not completely dry, as any moisture in the compressed air will also freeze and contribute to the problem.

If the first stage freezes open, the second stage regulator is designed to open as a failsafe feature. This rapid air flow can in turn lead to icing of the second stage, but it’s better that your demand regulator starts delivering unwanted air than the alternative, which would be to blow out hoses or unexpectedly inflate your BC or drysuit. Even on land, taking a “test” breath from your regulator in near-freezing temperatures can cause the moisture in the atmosphere and your breath to cause icing in the second stage, so when it’s cold, you should always wait to breathe through your regulator until already submerged. Even a quick press of the purge valve in cold air can cause your regulator to start roaring like a jet at takeoff, so be sure to avoid that as well.

For divers with a redundant gas supply, shutting off the tank valve and cutting off the air supply to the regulator might allow it to warm enough to function properly after a few minutes. If this happens underwater, breathing from your buddy's octopus while you do this is not a good solution, as that regulator is likely to be close to free-flowing too, and increasing the air flow through it by adding the demands of a second diver’s breathing is only going to result in another free-flow. The best remedy to free-flows is prevention. For this reason, there are a number of regulators that have been designed with heat sinks, environmental sealing, or other features that make them resistant to this problem.

Using a cold water regulator is a good idea, but next to that the best thing you can do to minimize the chance of a free-flowing regulator is to minimize the demand on it. You can do this by avoiding heavy breathing, adding air to your BC in small bursts, and avoiding using your regulator for things like inflating lift bags.

Give it a try
Diving in the colder part of the year can certainly be a challenge in New England, but armed with a little know-how and the proper gear, it can be quite rewarding. Even if you can’t picture yourself heading to the beach with snow on the ground, these tips should help to keep you diving comfortably through most of the autumn and spring. Stay warm, be safe, and above all have a great time!

Happy diving,
Matt Silvia

[cummings66]

I might get out of my drysuit and put a jacket on over the under garments and wear a hat, but that's about it.

[SkuaSeptember]

The only thing that I would add is that if my SI is going to be short ie just changing tanks I don't bother stripping down but instead just throw on a hat and a parka thats big enough to go right over my suit - wet or dry. For about $20 at Goodwill or the SA store you can get something big, insulated and windproof.

[navyhmc]

Usually, I leave the wet suit on, add a heavy coat. The cocoa is a good thing. Before you go in again, warm water in the suit is a must.

[dutchman]

Wow Matt, that was excellent data. Thank for sharing.

[cummings66]

I might be brief, but I assume in 37 degree water that any sane person is in a drysuit. It'd be foolish to be in a wetsuit in those temps. I have found through trial and error that how warm you feel in the drysuit during the SI really depends on the squeeze more than anything else. If you got chilled it really does help to get out of the suit and wear more layers. The drysuit is dry and you won't get cold putting it back on so there's nothing to lose by taking it off. If it's raining, sleeting or snowing I leave it on. If it's just cold I take it off and put a jacket on over my under garment.

I have dove this way down to about 0 degrees F, 36 degree water and have never found it to be a problem. When it's 0 or below freezing I will try to minimize the SI and get back under water ASAP. If I must have a long one and it's cold out it depends really on whether I can get back in the car or have to stay outside.

Before my tank comes off by the way, the suit gets inflated. It does help to make it real roomy inside, you've got to allow the under garment to air in order to warm up. I still feel adding another layer on top works better than just airing the suit.

In the end you do what you can to stay warm, I try to avoid fires and heaters for fear of melting a hole in my drysuit.

In the finest tradition of the Internet I've posted a long clarification in order to say what I do varies depending on temps and conditions. There is no magic mojo that helps. PS, it was 33 degrees outside when my avatar was taken. My daughter hopped out to get the pic and then back in. I stayed in the water floating during most of the SI's because it was warmer than the air temp.

[navyhmc]

Absolutely true Matt, there is no magic mojo. Me personally, I enjoy cold weather. Within reason, the colder the better. I also enjoy diving cold weather. My first ice dive were in a wet suit and it was years before I went dry on ice dives. In fact those in dry suits were initially referred to as whimps. Now, I call them the smart ones.

I have found though that those who enjoy the colder weather and colder temps far tolerate the cold water better than others.

I do a some winter camping and have done a few winter exercises with the USMC and I have always told my folks that cold is an attitude! If you look at the thermometer and say "Cool! -15*!" you do a lot better than the person that says "Holy Crap!!! it's 15*!!!!" Being prepared is another part of it too.

[dutchman]

OK, I understand the point about using warm water for priming. Like the mitt glove idea although I have never seen these. Understand about possible free flow. I assume you would never put warm water on the 1st & 2nd stages before diving !!! Still, I dive wet with the new Pinnacle Extreme semi dry. If you are at a lake, do you bring a tent, heater, chair, etc or just make a mad dash to the car? I would think a heavy blanket on shore would be beneficial when exiting the water. The hot coffee or mocha would be a real treat. Maybe even mint tea and some trail mix. It sounds like very little socializing due to trying to stay warm.