Re: Good sleeping bag for sailing
Herve, "warm" is a relative concept. I'd agree with fleece being the best thing on a boat. Down is useless when wet, and the fiberfill type bags also keep and hold a lot of moisture. If fleece will do the job, use it. Two or three layers, or a bag topped with a blanket, and you've got a lot of flexibility. Easy to wash, easy to dry.
If it needs to be waterproof, look for military surplus GoreTex "bivvy sacks" or "ECW" extreme cold weather shells. The shells are sold separately, bags with waterproof outer layers are still somewhat rare and expensive. And as noted, not always a good idea unless you really need them.