[Paddlewise] Layering wetsuits

Math has never been my strong skill, so work with me here.  I've participated
in various discussions about wetsuits and layering, and I'm concerned, as we
in the mid-Atlantic get into the transition months where cold water protection
is needed but drysuits might be overkill, that I don't get the math!
Specifically, is it the opinion of members of the list that layering a two mil
thick vest and a pair of rodeo shorts --- and let's use neoprene and not the
new Malden fabrics for the sake of argument --- over a two mil longjohn yields
the protection of a four mil wetsuit in the core body areas? I had always
accepted the idea that it did --- but then I started thinking about the way
these things work.  

When we swim, roll, low-brace, etc., water replaces the air between the suit
and the body whenever and wherever it can inside the base layer longjohn.
Physics is physics.  The process continues until the air is fully replaced by
the water --- let's say for a swimming kayaker --- and, unless the suit is
loose or is exercised in to a significant degree, the water will not flush in
and out of the suit a great deal, is warmed by the body, and a possibly
degraded but relatively stable body temperature can be achieved, with the body
continuing to produce heat to warm and hopefully stabilize the water inside
the suit.  The neoprene longjohn now acts (1) as an insulator from the outside
colder water mass which would otherwise quickly suck all the heat from the
body and (2) as a tight barrier, keeping a heat-stabilized water mass of a
minimum size against the skin.

But what about that second two mil vest and shorts over the longjohn.  The
ambient temperature (cold) water replaces the air between the neoprene layers
but, unlike the layer next to the skin, there is no direct contact with the
body to warm this water layer.  If the baseline longjohn is thermally
efficient, body heat should not be transferred through the neoprene's
insulating layer; obviously, the insulating powers of two mil neoprene are
limited, so some amount of heat will escape, potentially be captured by the
water between the two layers of neoprene, and, in turn, be insulated from the
outside water mass by the second layer of neoprene.  But does this second
layer have anything close to the same insulating capability as the first?
Seems to me it's very unlikely that there could be any measurable increase in
thermal efficiency from the vest and shorts over the thermal efficiency
provided by the longjohn.  Having always accepted that there <was> a value in
layering neoprene, I'm now concerned that the idea was bogus all along.


So, does two plus two really equal four?  Or does it equal two point one five?
Or three?  I'm pretty sure it's not anywhere close to four!  This isn't an
idle question --- it's getting colder on the Chesapeake.  I've been working
with a premise that I now think is flawed.  This isn't an idle how-many-
angels-can-stand-on-a-pinhead question --- nor is it designed to fill the
current information vacuum on PaddleWise. Any thermal engineers out there?
Divers?

Jack Martin
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