JcoldwaterIL:
Ive read that some drysuit undergarments will keep you warm even if your suit floods. does anyone have any experience with this? I'm sure a slow flood would be better than a fast flood as far as having an undergarment that keeps you warm while wet, but will it really work? And if it does work, to what extent at what temperatures? Anyone have any expereince with this?
Drysuit undergarments generally work in one of two ways. Either they "trap air" (or argon) which functions to insulate the diver, or else they use "thermal reflectivity" to reflect the diver's body heat. An example of the first category would be something like a Weezle or a garment made from polarfleece layers. An example of the second category would be thinsulate layers which can look like an aluminum foil laminated to a mylar or other polymer layer, generally sandwiched in between other fabrics.
Conventional wisdom (which can either be considered true or urban myth debunked, depending on the diver's susceptibility to cold, how cold the water truly is, and how long the decompression obligation is that requires the diver to remain submerged regardless or risk a hit that might put them in a wheelchair) holds that in cases where the diver who tears a seal in cold water but has mandatory deco to do should dive with a thinsulate undergarment. The rationale is that a flooded drysuit with an undergarment that requires loft to insulate the diver will, once that undergarment is flooded, lose that loft and hence will no longer offer any thermal protection to the diver.
In contrast, a thinsulate undergarment that reflects the diver's body heat back inward should in theory - even if the suit floods - continue to reflect at least a portion of the diver's body heat, thereby retaining at least some of its thermal protective properties.
In reality, hypothermia will kill the diver just as quickly as a DCI hit given too long a mandatory deco obligation with a flooded suit in extremely cold water. Given too many extremes, it likely doesn't matter what sort of undergarment the diver is wearing.
Still, it very well may be true that in moderately cold water a diver with a considerable deco obligation and a flooded suit may be significantly better off with a thinsulate undergarment. (We're not talking here about a recreational diver who, despite a slow leak in their suit, can continue their dive awhile and then get out of the water whenever they become uncomfortable. Instead we are referring to a situation where the diver MUST stay in the water due to a substantial mandatory decompression obligation. My definition of "extremely cold water" would be something in the 30s (fahrenheit) or low 40s. Say Lake Superior, for example.) In terms of experience, my own includes a 40 minute sojourn in a flooded Viking drysuit wearing a Weezle. I redefined my own definition of the word "cold" that day, and when I return to the PNW I will be diving a thinsulate undergarment...
Your mileage may vary.....
Doc
