As AC-DC says think of a dry suit. I am not sure exactly how they differ from an immersion suit but I suspect they are far more comfortable. There is a good range designed specifically for sailing and available from most chandlery shops. I suspect they are easier to get in / out of and there are even breathable ones available. Their warmth is a factor of the clothing worn underneath. With a few layers they work well even in very cold water. . .. .I would be interested if anyone knows precisely the differences between an immersion suit and a dry suit having used the latter but not the former.. .. .I am not sure about your comments regarding the weight of a life raft. 4 man self inflating rafts are available which weigh around 8 lbs.