Constanzi Stern of the Queen Mary 2

I've read accounts where things like that have been used for different reasons, including limiting squat on an old boat so it would go a bit faster.

But I thought you touched on the reason for those earlier: that they helped to reduce roll. Compared to the displacement of the whole ship they can't be adding much if they're barely in the water as you seemed to indicate. That means that as the boat rolls they represent an immediate change in displacement to resist same.

Maybe it's a bit like a stabalized monohull, resisting rolling but since the added displacement isn't much compared to overall the result isn't a fast rolling motion (like with a catamaran or trimaran)? Just reduced and maybe only a bit stiffer.