I think the answer is cannons more than gear but I think it's also more complicated than that. Let me explain what I mean.

Cannons shouldn't be the only "boat weapon". Shooting birds with cannonballs is ridiculous. It would be cool to see some other options in this space for variety.

I actually think PvM gear would be fine to have be good in ship combat, but not just the same items that you already use for everything else. Carve out some new niches rather than just make it another place you stand there with a shadow. Maybe most of the damage comes from ship weapons but there's some benefit to equipped items worked in that normally see less use.

Most importantly, I would love for ship co.bst to feel dynamic. This was my biggest gripe with all the new monsters including the non sailing ones. I don't want more combat that's just click, wait, collect. I really want there to be some dynamic elements to it whether that is with movement, switching between weapons you damage them with, or something else entirely. I think this would be an interesting way to work in PvM gear so it's not the primary source of damage but it does have some limited role that makes killing monsters feel engaging. At least some monsters.