Just a correction...

When you're in the water, the air in the suit does not contract (significantly) due to cooling. Rather, the air is compressed by the surrounding pressure in the water. If you put your feet straight down, you'll notice the suit is tightest at your feet since pressure increases with depth in the water. This is called a suit squeeze and shouldn't be of concern to sailors. Divers, on the other hand, must add air to thier drysuits to counteract the compression as they move deeper. The lack of inflation/deflation valves on sailing suits means you can't use your sailing suit for diving if the thought ever crossed your mind.
-Robert