If you head offshore beyond a reasonable swim to the beach, then you need to have a survival suit for every person on your boat. Think that’s too strict? I’ll give you a pass only if you sail the tropics—and only during the summer. (The waters off Key West were 69 degrees in January. Think you’ll survive in waters less than 70?)
The rest of you should have survival suits onboard. They may not be required for pleasure boats, and I know they are expensive, but you could say the same things about EPIRBS. The minimums aren’t always enough.
What is a survival suit?
They go by a few names: survival suits, quick-donning immersion suits or gumby suits. No matter what you call it, a survival suit is typically not a dry suit (though some models come close). Survival suits are not designed to keep all water out; they are designed to keep heat in. They do this by providing a layer of insulation, typically 5mm of neoprene, and restricting the flow of water next to the body.
Also unlike dry suits that are designed for constant wear in adverse conditions, survival suits (of the less-than-$400 variety) are designed to be put on within a minute, right over your clothes and shoes. Donning in the water is difficult and borders on unlikely in bad conditions, but it can be done, and any water inside will be heated by the body.
Survival suits also provide adequate flotation. That feature, along with insulation from cold water, allows them to dramatically extend survival times.