Does water in a wetsuit help or hurt. A myth to be BUSTED or CONFIRMED

[dumpsterDiver]

Yep. But I don't think it was ever claimed that the water was a source of heat, just a reservoir of heat.

Right. Or, rather, 37 degrees (C)

The reason for the calculation was that I didn't believe that there was enough water trapped inside the suit to effectively work as a heat reservior, like archman claimed it could. And my numbers supported that belief. I looked at the problem from an idealized best (for archman's claim) case POV and didn't consider the fact that I first had to spend heat to heat that water to body temperature, which only serves to make the deal even worse.

Yes you and I completely agree, the "biologist" is full of crap on this one. And I was trying to clarify the inherent assumption in your calculation.. namely that you were as generous as possible in trying to verify archman's argument....

---------- Post added August 22nd, 2013 at 04:56 PM ----------

The whole question as presented by the OP was silly, of course letting cold water into your suit does not warm you up (or keep you warm).

However, I have heard a more interesting argument that is related. The argument goes like this... pre-filling your well fitting wetsuit with very warm water immediately before a dive will cause you to be chilled faster. I know it sounds counter-intuitive, but the argument was that bathing the extremities in a thin layer of very warm water, cause vasodilation in these areas. So even though the warm water feels good at first, it reduces the body's natural reaction to conserve heat by shunting blood flow to the extremities and thus reduces your ability to withstand cold water for a long time. I guess their experience was that by the time the skin felt cold, you had lost more heat than was added by a thin layer of warm water.

This has some similarities to the situation where people are cautioned not to drink excessive alcohol when subject to very cold air temperatures because even though the alcohol may deliver a feeling of a warm "flush" the alcohol causes excess blood flow to the skin and this accelerates heat loss.

I know for a fact that if you keep adding a new supply of externally heated water to your suit, you will stay warm longer..but this was described as pre-filling the suit only one time with warm water..

 

[redacted]

I know for a fact that if you keep adding a new supply of externally heated water to your suit, you will stay warm longer..but this was described as pre-filling the suit only one time with warm water..

Priming the suit with warm water is a good start when your neoprene is just not up to the temperature at hand. Adding a chemical heater or two can make an otherwise very cold dive quite comfortable.

 

[dumpsterDiver]

When I used to commercial scuba dive all day in sub 50 degree water in a wetsuit, I used a chemical heat pack and had a cooler of hot water to keep adding to my suit. Both techniques can extend your time by a large margin.

 

[johnmckenzie]

I want to thank all those that posted for the help. I am very impressed with the intelligence of the dialogue. It is so unlike the stereotype of forum posts. I will take the replies and try to come up with a summary to take to the experts and agency execs who prompted this question. I will keep an eye on this post for anything new, post back my summary and share anything more I learn.

---------- Post added August 22nd, 2013 at 11:20 PM ----------

p.s. I don't want to presume I am the best person to summarize this. In case anyone is inspired to summarize... I want to end up with an short, accurate, practical and understandable statement (non-condescending) that we can all use to help the broad range of students and other divers clearly understand this issue in a way that the myth becomes a thing of the past.

 

[Panama Jones]

----- Post added August 22nd, 2013 at 11:20 PM ----------

I want to end up with an short, accurate, practical and understandable statement (non-condescending) that we can all use to help the broad range of students and other divers clearly understand this issue in a way that the myth becomes a thing of the past.

Let's trust the BSAC on this. Al of their water is cold and we all know that anything said with that fine British accent always carries a fair weight of credibility so here's two credible BSAC sources.

Essential items you will use in scuba diving.
Wetsuit or drysuit
Depending on where you dive – in warm or cold water – you will need a protective layer of clothing. In warmer waters, a wetsuit is used, which is made of a layer of neoprene rubber. This acts as insulation by trapping a thin layer of water next to the skin which the body then heats up. The colder the water, the thicker the wetsuit.
http://www.crabbsac.org.uk/articles/A024.htm
Myth: Wetsuits work by trapping a layer of water between your skin and the suit, which warms up
Fact: The insulating in a wetsuit is done by the gas trapped in bubbles in the neoprene. Water conducts heat very well. The less of it you get in your suit, the better!

 

[drbill]

I can't answer the question definitively for wetsuits, but I sure can tell you that 4-5 gallons of water trapped in a dry suit does NOT keep you warm!

 

[Insta-Gator]

I always let some water in. Allows the suit to move into a comfortable pisition.

Sent from my SCH-I535 using Tapatalk 4

 

[eponym]

Not scientific data (as requested by the O.P.) but . . .

My local waters are at best 70F, and usually in the 55F-40F range.

If I'm diving wet, I can choose my 5-mil suit, 7-mil suit, or 6.5-mil semi-dry suit.

I take on almost no water at all in the semi-dry (S'pro Nova Scotia) and I can do a heck of lot more diving in that suit than in a traditional 7-mil wetsuit before I start calling the dives due to cold.

I have seen several students who bought semi-dry suits demonstrate the same thing on cold-water training dives.

My conclusion: the less water in the suit, the longer I can go before I'm too cold to continue.

-Bryan

 

[Frosty]

I dunno about scientific stuff on this subject just personal experience.There is a layer of warm water between me and my suit when I'm diving.
How that happens I dunno.

 

[Foxfish]

Not real sure why this is so confusing. 'billt4sf' pretty well nailed it in his comments post 26. To reiterate, heat is transferred by conduction, convection and radiation. Radiation can be discounted as negligible since it mainly occurs at high temperature. You can feel the heat transferred through radiation by standing in front of an electric radiator heater or the coals of a fire.

If you hold a steel bar at one end and heat up the other, eventually the heat will travel through the steel bar to your hand providing the bar is not too long. That is conduction. If you wind the windows down when starting off in a car that has been sitting in the hot sun the hot air gets blown out and replaced with cooler outside air. That is convection. If the bar in the heat transfer by conduction example was long enough then you'd find that a lot of the heat would be dissipated into the air by convection and there would be little if any temperature increase at the hand holding the bar.

Now how does this apply to the various dive suits? Your body is typically at a higher temperature than the water so heat flows from your body to the water.

A wetsuit minimises heat transfer by conduction and convection. It provides at least some insulation. If you want to be technical, the wetsuit has a lower conductive heat transfer coefficient K (W/mK) than the boundary layer would provide at the skin/water interface. In addition the wetsuit serves to minimise the water movement at the skin/water boundary layer and so reduces heat transfer due to convection. Some water will still flush through the wetsuit which means that there will still be a significant amount of heat transfer through convection. That cold blast of water you feel down your back is the cold water is convection ie. cold water displacing warmer water. Not a bad thing for those who pee in their wetsuits. Some people wear an extra layer under their wetsuit to stay warmer. That will reduce the heat lost through conduction but if you still have water flushing through the suit it probably won't make as much difference as you would hope.

Enter the semi dry. I've got a 6.5 mm Nova Scotia semi dry and turn the ends over at the ankles, neck and wrists to provide a seal at these locations. The zip is also a better seal than a typical wetsuit zip and is aligned horizontally across the back which reduces the amount of water flowing in past the neck seal. I used mine on the weekend in water that was 19 degrees C. As I took the suit off after a dive about half to one litre of water poured out of the suit. You can feel the water is warm water and no I didn't pee in the suit! It gets heated up because it is trapped and close to your body. The heat transfer through conduction won't be a lot different to a wetsuit the same thickness but the convective heat transfer will be a lot less because there is less flushing of water through the suit.

A dry suit is potentially the warmest which is why they are worn in frigid conditions. There is no heat transfer through convection if the various seals hold. I've never worn a dry suit. An air gap will certainly reduce the heat transfer through conduction but my guess is that the suit would to some extent cling to the diver and at those locations the air gap would be minimal. Wearing an undergarment would help to maintain the air gap and hence improve the insulation properties of the suit and minimise heat transfer through conduction.

My guess is that most of the heat loss is through convection ie the action of water flushing through a suit but I'm still uncertain on this one. The deeper you dive the more the wetsuit is compressed. This will reduce the suits insulation properties and increase the heat transfer through conduction. I'd probably be cold in water at 18 degrees C at a depth of 25 m in a 2 mm semi-dry (if such a thing existed). A 2 mm dry suit is not uncommon and I'd be interested to hear if divers find this adequate or would need an undergarment in these temperature. It seems likely that the material in a dry suit provides better insulation than a semi dry suit. It seems to me that water can permeate through a semi dry suit which would explain the better insulation of a dry suit but I'd need to have that confirmed.

On the question of the relatively high heat capacity of water, that would only be a benefit in a semi dry suit. My experience is that the dive suit reaches thermal equilibrium fairly quickly. If the heat loss through conduction is relatively small then increasing the reservoir of water trapped inside the suit won't provide a lot of extra warmth. It wouldn't be hard to let in a bit of extra water into the suit and see if it this makes any difference. You'd be colder for a lot longer at the start as the water inside the suit heated up. I've never seen any discussion that doing so provides any significant benefit.

---------- Post added August 25th, 2013 at 11:36 PM ----------

The short answer is as follows:

Heat is lost through the water that flows through a wet suit or semi dry suit. The less water flowing through the suit the warmer it will be. That is why a semi dry is warmer than a wetsuit. Water is not a good insulator. Air is. That is why dry suits are warmer than wetsuits or semi-drysuits.