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SurfLung
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Wet Suit Logic

Sun Sep 24, 2017 11:54 am

Wet Suit Logic
- I dive a 3mm wetsuit in temperatures down to 39 degrees F (and lower) at Fortune Pond. I've been doing it for 5-6 years now and have not died of hypothermia. Usually they are 30-40 minute dives but I have done a few for nearly an hour when we did the last half of the dives at shallower and warmer depths. I've tried thicker suits and other combinations and have formed some opinions I'd like to share.
- Suit Thickness and Warmth - While it is true that thicker wetsuits are warmer at the surface, the advantage becomes less and less the deeper you go. For example, a 5mm suit is compressed to 2.5mm at 33 feet. A 3mm compresses to 1.5mm... So there's only 1mm difference. And the difference becomes less and less the deeper you go. There's been some discussion about how the original "Rubbatex" wetsuits were less compressible than modern suits. I believe compression isn't the only factor and modern suits have several advances that make them better than Rubbatex.
- Other Warmth Factors... Modern suits fit better, so there's less cold water flushing in and out. Modern suits have advanced thermal linings that insulate via the lining properties rather than the suit thickness. Modern suits can be "semi-dry"... I have BARE brand wetsuits that won't drain water out the ankles unless I pull the cuff open to let the water out. I remember one of these suits still had a dry spot inside after a dive.
- Targeted Warmth Strategy... I wear a 3mm hooded vest under my 3mm suit. This gives me 6mm of thickness over my core. But remember this compresses to only 3mm at 33 feet. I think the added thickness contributes, but I also think that the hooded vest seals the hood/suit joint better than just a hood and restricts water from flushing in and out. I've tried wearing the hooded vest on the outside and it didn't help my warmth at all... So, added thickness alone without restricting cold water flush isn't much help.
- After Dive Warm-Up Strategy... I used to unzip and pull off my wetsuit top but leave the pants on between dives. I noticed that I felt coldest AFTER a dive than during the dive. I read an article about the wet suit actually becoming a refrigerant due to the evaporation of water... The article said to get the wet suit off ASAP, dry off and put dry clothes on. Wow, what a difference that made in warming up between dives.
- Why Do I Prefer a Thin Suit? Mainly because there's less influence of suit compression on buoyancy. I can wear less weights. I rarely put any air into a BCD (when I dive one). And, a thin suit is less confining.
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Ron
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Re: Wet Suit Logic

Sun Sep 24, 2017 2:20 pm

While I agree with all of this, and I think many people would, there are 2 points I'd like to add:

1.) Not all wetsuits compress universally IAW Boyle's Law. It is not fact that a 7mm wetsuit will always be 3.5mm at 33 feet. Hence the anecdote that older, less compressible suits were warmer.

2.) This all ends up being a body type thing. I wear a 5mm skin in freediving suit in Puget Sound. Freediving suits are the warmest wetsuits I've ever worn, as they are unlined and exchange almost not water. Sometimes my chest is dry in mine. I last 30 minutes tops in the sound, and it is generally 50 degree sea water. If I work a 3mm with a vest in 39 degree water, I'd get hypothermia in probably about 25 minutes. That's anecdotal, but I've actually gotten hypothermia before (yay Army), so I feel like I have a decent barometer for it. Biology really makes all the difference. I bet when you were a 125 pound teenager that there was no way you could've done this. I'm not a tiny dude either. I'm 6 feet tall and 200 lbs. You either have enough body fat or you don't, so to speak.

I prefer diving in a wetsuit over a drysuit too, but where I live leaves me little choice outside of summer. I think I'm going to get a 7mm Elios-sub for summer diving here next, and it's going to be an unlined suit as well. Unlined wetsuits really are the best ones for warmth. Layering, although accurate in the sense that you are introducing more blown nitrogen to insulate you, introduces coldness as well. Multiple layers of lined neoprene allow water exchange, which introduces both conductive and convective cooling. All things being equal a 6mm wetsuit chest area with 3mm arms and legs is warmer than 2 3mm chest areas that are separate. There is a bunch of data on Rubicon if you are interested.
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luis
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Re: Wet Suit Logic

Sun Sep 24, 2017 6:23 pm

I agree that reducing or stopping the water from circulating is extremely important, but insulation thinness is also very important.
SurfLung wrote:Wet Suit Logic
- Suit Thickness and Warmth - While it is true that thicker wetsuits are warmer at the surface, the advantage becomes less and less the deeper you go. For example, a 5mm suit is compressed to 2.5mm at 33 feet. A 3mm compresses to 1.5mm...
This could only happen if the insulating layer was 100% air and 0% neoprene rubber.

Solid neoprene rubber for the most part doesn’t compress very much at all. You can squeezed / compressed it in one direction and it flows/ expands in the other directions.

The insulating neoprene is expanded with gas into a foam, but it is far from being mostly gas.

I have dove to 4 atm (99 ft) with 7mm neoprene several times and it does compress, but not that much. The buoyancy change and the overall material thickness change are not really proportional. The gas compresses, but the neoprene rubber doesn’t.

I get cold easily and I always used to wear a two piece 7mm + 7mm (farmer john) + a 3 mm hooded vest. The hooded vest on top of the farmer john, but below the jacket provided a great water stop to prevent any water exchange.

Now my favorite cold water wet suit is the Aqua Lung SolAfx. It has 8 mm on the core, an attached 7 mm hood, ankle and wrist seals, and a extra barrier under the zipper to avoid water circulation. I still wear a 3 mm vest under it, some times.

It is by far the best wetsuit I have ever used. In the water it is almost as warm as my dry-suits. But I will still wear a dry-suit when the air temperature is cold. Changing out in cold air when it is cold can be brutal.

http://www.aqualung.com/us/dive-gear/wetsuits/solafx

BTW, in the spring, when the air temperature is warm but the water is cold, I have been known to use electric heat (Thermalution vest) under my SolAfx wetsuit. Did I mention that I can get cold easily.

Under the ice I have only used dry-suits with nice heavy undergarment. When I traveled to Washington state and dove in Puget sound I only took a dry suit and some medium/ heavy undergarment.


Here is some general data for future use.
Density of solid neoprene
0.05 lb/cuin = 86.4 lb/cuft
Specific gravity about 1.38

Thermal conductivity
Air 0.024 W/(m K) = 0.0139 Btu/(ft*h*F)
Neoprene 0.05 W/(m K) = 0.0289 Btu/(ft*h*F)
Water 0.58 W/(m K) = 0.34 Btu/(ft*h*F)

Some other materials thermal conductivity, just for reference to compare.
Aluminum 205 W/(m K) = 118 Btu/(ft*h*F)
Concrete 0.7 W/(m K) = 0.4 Btu/(ft*h*F)
Cork 0.07 W/(m K) = 0.0405 Btu/(ft*h*F)
Timber Oak 0.17 W/(m K) = 0.098 Btu/(ft*h*F)
Water 0.58 W/(m K) = 0.34 Btu/(ft*h*F)



This looks like an interesting article, but it cost $25 to download it. I may buy it when I have some time to read it
http://thermalscienceapplication.asmedi ... id=1469410

Here is the Abstract
The purpose of this paper is to present a correlation for predicting the thermal conductivity of foam neoprene at varying ambient pressure. In a previous study, the authors used well-known upper and lower bounds to develop the form of a semi-empirical correlation for the thermal conductivity of foam neoprene as a function of increasing ambient pressure. The correlation was in terms of three constants, which were determined by performing a nonlinear regression on experimentally measured thermal conductivity values of foam neoprene insulation at varying ambient pressure. In this present paper, we show that the three correlation constants can, alternately, be determined by using values of the constituent thermal conductivities (e.g., air and rubber) and the effective thermal conductivity at one pressure point only (reference pressure). Values predicted using the correlation were compared with previously measured values of the effective thermal conductivity of foam neoprene insulation under increased ambient pressure, up to 1.18 MPa. It was found that there was a maximum difference of approximately 14% between the predicted and measured values. It was also found that the accuracy of the correlation did not depend strongly on the reference pressure used. It was therefore concluded that the effective thermal conductivity of foam neoprene, as a function of increasing ambient pressure, can be predicted if the constituent thermal conductivities are known (air and rubber), as well as the effective thermal conductivity at one reference pressure.
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SurfLung
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Re: Wet Suit Logic

Wed Sep 27, 2017 1:33 pm

Cold Management Plays a Role
- I'll use the example of sitting in a deer stand to illustrate: You can get really cold sitting in a deer stand. It breaks your spirit and you forget how bad you want to shoot that big buck. But then you get out of the stand and start hiking back to camp and by the time you get there, you're hot and sweating. Increased blood flow from the exercise of hiking? I remember thinking once, "Why can't I just turn this heat on when I'm freezing in the deer stand?" Nowadays I "manage" the cold by bringing a thermos of hot coffee and snacks... The hot drink helps my core temp but also gives me something else to think about besides cold. And usually if I can last until 9:00 AM the urge to go someplace and warm up subsides and I can last the rest of the day.
- Second example is diving in Fortune Pond. When you start a dive, you head down through the thermocline and the exposed areas between your mask and hood will actually ACHE from the cold... Until you get used to it. At this point in the dive, I feel the cold on the rest of my body from incoming water in my suit. Again, I "get used to it" and then I can be diving comfortably for 30-40 minutes. BUT... If I ascend above the thermocline and feel the warmer water, going back down to the colder water gives me a chill that I can't get used to, and I need to get out.
- Third Example is that I'm actually comfortable at the end of a 40 minute dive but start to shiver with cold as I start taking off my gear and suit in the breeze. I learned from a dive magazine that at this point, the wet suit becomes a refrigerant... Evaporation cools. Getting the suit off, toweling off, and getting dry clothes on cuts this shiver time down to just about zero.

And What About Modern Linings?
- The latest advanced lining from BARE Wetsuits is called Celiant Infrared Technology. And it claims to turn heat into infrared energy that reflects back into the diver. Studies show infrared energy increases blood flow... Hmmm sounds like a way to turn on the heat in my deer stand! BARE is combining this with better sealing 'No Stitch Technology" to make a suit warmer.
- I also heard awhile back about some wetsuit company actually using Merino wool in their linings. It claimed not to increase buoyancy but I don't know how.
- And Sea Hunt Jerry had a suit with smooth skin inside that had some sort of heat reflective coating. What about that?
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Re: Wet Suit Logic

Wed Sep 27, 2017 7:59 pm

When I dive wet up here I normally keep a few plastic thermos with hot water in the car. I always prime my wetsuit with hot water (or at least warm water) before I enter the cold water dive. I do this unless the actual water temperature is relatively warm and I am only using a very light wetsuit.

Priming the wetsuit cuts the initial thermal shock, but what is far more important is that it cuts the total amount of calories spent at the beginning of the dive (needed to heat the water).

I also save at least one thermos of hot water to fill my wetsuit when I get out. This hot water heats me back up and allows me to change out of my wetsuit in comfort. Only when the air temperature is cold and breezy it becomes a problem, and I dive dry.



I am always very skeptical when I read or hear about advertising claims of clothing that reflects radiant heat back to your body. They rarely pass the straight face test, for an engineer with heat transfer and thermodynamics background. I am not saying there no contribution, but when you are in direct contact with the clothing, conduction at this temperatures is the dominant form of heat transfer. And I am talking in air… in water, in a wetsuit…

I am not totally ruling them out, but I am very skeptical about the claims.

Radiation heat transfer is used in many heating systems, but you may notice that the heat source is normally very hot. It is a great means of heating a person without heating all the air around us. This would be a lengthy subject to explain so I will have to come back to it.

The Merino wool liner and the smooth inside skin do seem to help a lot in very different ways. The smooth skin basically sticks to the skin and prevents water circulation. They are a pain to put on though.



BTW, another interesting point about staying warm. When we are in the outdoors we always talk about moving and exercising will warm you up. That is very true in air, but not in the water. Whenever you are submerged in water, if you move, you will increase the convection heat transfer. The more you move the more heat you will lose due to convection into the water.

The increase heat generated by exercise is no match to the increase heat loss by moving in the water.

Many people will argue that they feel warmer and I will never argue with perception, but that is just a perception. It has been proven again and again that survival in cold water is extended by staying still. It doesn’t matter what type of insulation or even survival suit one may be wearing. That is why the Coast Guard insist that the flotation of a PFD will save lives. You can stay still and save energy.
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Re: Wet Suit Logic

Wed Sep 27, 2017 8:30 pm

So that's what it's called - "Priming the wetsuit." I've been doing that for years. One of our So. Cal. dive boats has an onboard hot tub. Great for dumping a bucket of hot water into your suit just before the giant stride into the briny deep.
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Re: Wet Suit Logic

Thu Sep 28, 2017 10:39 am

ScubaLawyer wrote:...One of our So. Cal. dive boats has an onboard hot tub...
Oh man... An on-sight hot tub would be the perfect solution at Fortune Pond. Check this out: https://theoriginalnomad.com/collection ... coil-combo
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Re: Wet Suit Logic

Thu Sep 28, 2017 11:16 am

SurfLung wrote:
ScubaLawyer wrote:...One of our So. Cal. dive boats has an onboard hot tub...
Oh man... An on-sight hot tub would be the perfect solution at Fortune Pond. Check this out: https://theoriginalnomad.com/collection ... coil-combo
Found a pic of the hot tub I spoke of on-line. We always get a ration of caca from somebody who chastises us for soaking in hot water following a day of diving. Something about drawing micro bubbles out and putting us at risk for DCS. Maybe true, but damn, does it ever feel good. :D
https://s3media1.fl.yelpcdn.com/bphoto/ ... Q/180s.jpg
"The diver who collects specimens of underwater life has fun and becomes a keen underwater observer. .. seek slow-moving or attached organisms such as corals, starfish, or shelled creatures." (Golden Guide to Scuba Diving, 1968) :D

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Re: Wet Suit Logic

Tue Oct 10, 2017 9:33 am

Modern Wet Suits Fit Better?
- On our last trip to Fortune Pond, it occurred to me that I might try my Sea Hunt wetsuit from Elios. It's only a 3mm like my regular BARE. But it's the vintage style front zip two piece with beavertail. I wore it with my 3mm hooded vest underneath and I have to say I was just as warm as I usually am with the BARE. I'm thinking that is in no small part due to better fitting technology of modern suits.
- The Elios suit truly fits me "like a glove". Elios has made a name for themselves making sleek smooth skin free diver suits and triathlon competition suits. So, I now realize that this is a REAL wetsuit and not just for the Sea Hunt Re-enactment shows.
- I think I'm settling on a conclusion that the main thing with wetsuit warmth is how well it seals from excessive water exchange.

Note to Self: To keep the smooth skin Elios from snagging when overhead donning twin 38s, try spraying your back with DIY wetsuit lube (50/50 Baby Shampoo and Water). At Sea Hunt Forever in Silver Springs, I smeared Vaseline on my tank bands to avoid snagging and tearing the suit.
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