Originally posted by Trike:

Have yet to discover what kills you in the ocean on a raft, but okay.

Well I don't want to spoil you so I won't mention anything specific. But ships can capsize under certain conditions, and rafts are the most prone to it. Karves are less prone to capsizing, but it is still possible. I've never seen a longship capsize, I don't know if it can happen.

Rafts are also by far the slowest, so it's good to upgrade just for the sake of your sanity. It's a big world out there.