Inspired by a thread on hull health by @HaxxorSauruz here: https://www.seaofthieves.com/forum/topic/51190/ships-need-a-health-system-to-promote-better-naval-combat
I think a good way to incentivize good cannon hits over the standard barrel + board, and also make the attrition-heavy naval combat a bit more interesting, would be to penalize you for having to plank repeatedly. If you are getting severely outgunned you shouldn't be able to keep afloat just by planking at the same rate you get shot.
For example, every time you plank the same hole it could take 50% longer than the previous patch - or, it could require you to plank it over twice (the first time cuts the water flow by only 50%). Next time require three planks, still leaking after the first two. Three planks is also a magic number because if you have multiple tier 3 holes, you have to hit up your supply barrel after each set of patches which makes it even more likely you'll sink unless you dedicate more crew members to patching.
This way in a galleon vs sloop situation where the sloop is wailing on the galleon with cannons and not getting hit much in return, eventually the galleon won't be able to keep up with repairs and sink. Right now it's too easy to have one guy on patch duty and just keep repairing until one ship runs out of supplies or a barrel gets snuck on board, which isn't super exciting.
You could represent this in game by having three or more "tiers" of hole that gets more ragged and/or noticeably larger each time. A tier 3 hole requires substantially longer to plank (and/or 3 planks), and each time the same hole is ripped open it upgrades to the next level. Give an option at Outposts to repair your ship and make it good as new. To discourage "drive by" repairing a galleon during a chase, the shipwright could require you to keep your anchor set within range for 60 seconds with no additional damage while she works on the hull.
Bonus: this might teach me to be a better driver if it takes longer to plank each time I beach myself on an island ;)
