Wadya know, they are both dive boats...
A 15' RIB would be sea worthy for the fjords or the North Sea wouldn't it? I've been out in 10 footers with a buddies RIB. I felt plenty safe and we were hitting the waves hard chasing a big black Zodiac that had twin 50's (SIB) taking pictures of it.
I did have to get a few stiches above my eye though when we hit the bottom of a trough hard and my underwater camera housing came up and hit me hard. Other than that moment I felt safe in the 10 footers...
Are you wearing a Poseidon Unisuit under the PFD? Cool photo circa early 70's?