I've often seen the waivers that some people sign for skiing and sailing that clearly state that the sport/activity has some inherent risks and that you agree to accept them.
I used to race on a edge-of-the-environment boat (M1) owned by a lawyer. Even as "regular crew", every one of us had to sign a copy of the "death waiver", every time we set foot on the boat. "Yes, I acknowledge that racing on M1 exposes me to the risk of injury or death."
Kinda silly at the time, but these days? Probably pretty smart.
but you can't waive the right of your health insurance company to recover damages from the owner or his insurance company if you get injured on the boat.
if you are a crew, the only way to make sure that your insurance company doesn't try to recover from the boat owner is to not tell them that you were injured on his boat.