Your boat capsizes but remains afloat what should you do?

Stay with the vessel as long as possible. It will present a larger target for search and rescue assets. If you have the ability to get out of the water and climb on the hull, it is MUCH better to do so. This will greatly increase you chance at survival if it appears you may be there for a while. Even if the air is freezing and the water is not, you are going to survive longer OUT of the water. Think of Jack and Rose, who survives, who doesn't.