I have cannons in the setting, just cos I wanted the players to be able to use them, cos fun! I’ve developed a way of doing ship-to-ship combat that has been working quite well.
I balance the encounter with a manageable number of enemies to match the party, and maybe one or two named NPCs. They battle it out while the two crews fight around them. The crews go in with a set strength rating that translates to a modifier. At the start if each round, both crews roll a d20 and the loser takes one away from their modifier. I determines the starting mod for the players by assessing morale if the crew, how well fed and we’ll armed they are, etc. I use the results to add flavour to the battle. So it’s like the party are fighting some of the crew, but I’m simulating a larger battle around them. If their crew is losing, the PC cam use their actions to affect the larger battle and swing it back in their favour.
Each turn, each ship can move its movement speed and fire cannons/ballet’s on either side. The players can use their actions to do these things or, if they have enough crew left, they can give orders to have them do it.
Makes are still very useful aboard ships cos they can do stuff like create a gust of wind for a burst of speed, or create a fog cloud for visual cover. Also fireballs!