Heat Pack vest?

[driebel]

I took my new drysuit out recently, and discovered that my insulation is insufficient for the 5C water I found. I'd like to beef it up, and in particular I'm thinking about adding an "active" heating layer. I'm envisioning a sort of vest with some chest area pockets that I can store a couple of chemical heat packs in. I've done some casual window shopping, does anyone have a favorite solution for this? The electric heaters are out of my price range, but some $15 heat packs and a $40 sweatshirt/vest isn't. Thoughts?

Dave

[Akimbo]

Here is my take on the priority for improving drysuit performance.

1. Always maximize insulation first. It is the simplest, most reliable, and least expensive in the long run.
2. Add an Argon bottle to purge and equalize the suit. This should yield about 30% lower conductivity — essential on Trimix. However, that will only save about 30% of the 50% heat loss through the suit. Respiration accounts for about 50% of our total heat loss. The downside is the ongoing cost and inconvenience of filling the Argon bottle plus the weight. Personally, I tend to add more insulation and lead on the belt to compensate for it unless on Trimix.
3. Active heating. There are lots of problems with active heating. Heat distribution, the BTU/Calorie to weight and cost rations, the time limitations, and the reliability all make it less attractive than the first two options.

The only active heating system that I have ever seen that counters this argument is the hot water heated wetsuit that commercial divers use. About 2½ GPM of 110° salt water enters the suit and is fed from the surface through an umbilical. Perforated tubes distributed the water throughout the suit and also heats breathing gasses.

[PfcAJ]

Be cautious of those heat packs. I've heard (never experienced, though) that they can get VERY hot due to the increased pressure. YMMV.

Investing in a proper undergarment (400g Thinsulate), a thick, quality hood (Wetwear, for example) and in your case drygloves are probably in order. Those measures plus argon (with purge) should help out. past that, a heated vest is in order (Santi makes one, as does Silent Planet and Golem Gear, and DUI is working on something), but they come at highly increased cost, risk, and complexity.

[driebel]

Good points, both of you. Thanks! Round two is this Saturday, and it probably hasn't gotten any warmer We'll add a (passive) layer or two and see how that goes.
PfcAJ, just wondering, what's with the He atom?

Cheers,
Dave

[asha]

+1 for upgrading your insulation. I resisted this for too long and was never truly warm as a result.

After a long struggle with being too cold in my drysuit, I think we've finally solved the problem with the Fourth Element Halo 3D. I do have a low-tech heated vest that helped but didn't really get me all the way there. It's made by Quiksilver, cost about $100, and is designed for surfing. I would strongly recommend this over chemical heaters because it has two heat levels and can be turned off through the drysuit if necessary. Once I bought the Halo (I was formerly in an MK1), I started leaving the heated vest on the boat because it made me too hot (!) in 12C water.

Layering sounds good in principle but can really affect your mobility. In a thermal shirt, the heated vest, and the two layers of MK1, I struggled to reach my valves. It's a lot easier in just the shirt and the Halo. I don't know what kind of insulation you're currently diving, but if you can, I would upgrade that first. Budgets are budgets, but like pretty much everything in diving (I'm slowly coming to learn), trying to compromise on price often results in a compromise on quality or performance.

[mathauck0814]

Heating the skin increases the risk of DCS by increasing bloodflow to an area that otherwise wouldn't have bloodflow. This becomes particularly concerning with chemical heaters as they're warm at the beginning of the dive (or series of dives) and cold toward the end. The risk becomes that early in the dive the warm skin allows those tissues to load inert gas and through cooling and decreased bloodflow those tissues become "slower compartments" that retain inert gas. It's largely theoretical, but DAN has a few articles to substantiate why localized skin warming is a bad idea. You're better off achieving warmth through heating your core internally by controlling heat loss. Saving a thousand dollars by not buying the correct equipment and taking a chamber ride will cost you in the end - even with something as minor as skin bends.

[Wantonmien]

driebel,

I'm a wetsuit diver, but with waters chilling last year, I invested in heated Tshirt for me, and heated vest for my divng better half from www.thermalution.com

On a recent dive trip, guys in 5 & 7 mm suits were cold in and out of the water, but wearing a 3mm, hood and the heated vest, no problem, warm as can be - has 3 levels of heating, though the lowest level is normally plenty.

Pricey yes, but for me the best bit of extra dive gear I ever invested in.

Cheers

[driebel]

That's a really interesting point about the localized skin heating and DCS that I hadn't thought of, but makes intuitive sense. For the record, I'm currently diving a DUI CLX450 suit, with the DUI hood and zip-gloves (dry). My insulation is a set of IceBreaker 260g wool thermals underneath the 4th element Xerotherm. In 5C (40F) water, I was shivering quite badly after 30min. After our surface interval, I added my sweatshirt (nothing fancy, just a sweatshirt, like from target) for dive 2, and was better (though not exactly comfy) for a quick 25min dive. My plan for this weekend (same dive site) is to start with the sweatshirt/pants from the beginning. Part of my discomfort on dive 2 was certainly residual from dive 1. That Halo-3D does sound nice, and it gets good reviews. Maybe next winter...

[mathauck0814]

The Xerotherm is pretty light weight and the thermals are better suited for skiing than diving (if they're the ones I'm thinking of). I'm not surprised that you're cold in 40F water. I find that I'm constantly negotiating between warm enough and having enough mobility. Try a bunch of undergarments on with your suit on if you can and have a look around at craigs list or the classified ads here - people are always selling their undergarments as they trade up. I've settled on a two piece DUI fleece undergarment but it's honestly not as warm as i'd like it to be - it's just the best compromise I've found that gives me the mobility to do the necessary tasks safely.

[ddmattos]

Xerotherm: Xerotherm Thermal Base Layer | Fourth Element
Arcitc: Arctic Extreme Performance Undersuit for Diving | Fourth Element

They should be layered in 40F water. Throw on the drybase if you still feel a chill.
Otherwise go with the xerotherm, Subx combo.

Darren