Instead of having whales just attack the knarr or rowboat why not take this as an opportunity to add some flavor to the game. Give the whale a delayed aoe cone attack in front of itself. Anything in the cone after a second or two takes massive damage including the knarr. Pretty much some sort of animation for a body slam on the knarr and riders. This gives the driver of the knarr the responsibility of keeping the group safe from drowning.
Contrary to popular opinion I do believe a whale should be able to damage a knarr, however I don’t think it should constantly damage it or do it quickly. Give the hearthlings a chance if they’re in open water. Seems like a good opportunity to add in new combat properties.
But jorb probably can’t draw a whale doing a body slam just like cave spiders.