A wet suit works by trapping a layer of water next to your skin and letting it warm to your body's temperature and act as insulation. It always fits skin-tight, and comes in thicknesses; typical light ones are 2-3 mm, standard is 5 mm, and 7 mm is heavy. They work well in colder water and warmer air; there is no evaporative cooling while you are in the water, and once you are back in the warmer air/sun, the cooling is actually beneficial.



When it's sure-nuff cold, a drysuit is the only way to go. It actually keeps you dry, and most are quilted or lined for warmth as well. They do not fit skintight, and are better for really cold water temps and cold air conditions.



Spray- or semi-dry suits are similar to raincoat material; never quilted but sometimes with thin lining. They are meant to keep the wind off, and work really well in cooler air/warmer water situations as well as for an outer layer over a wetsuit, to cut down on wind-induced evaporative cooling.



hope this helps; I sail in Texas and own a shorty wetsuit and a full body spray suit as well as a spray top. First line of defense is the spray top over a t-shirt; next line would be spray top and shorts over the wetsuit, then spray suit over wetsuit, then I suppose spray suit over fleece over wetsuit...then it's too damn cold for me, and you can go sailing by your own self if you're that crazy! of course, water temps in the 40 are not something I have experienced, and my yacht club (mostly monodulls, admittedly) will not start a race if windchill is below freezing.



good luck, and

sail fast