So this could be a case of me missing several times in a row with a Level 70 Galleon against several low-level ships ( which would be very cruel ), or I've discovered a bug which somehow went unnoticed after all this time.
While fighting the Cutthroat Ships near Isle of Dogs for the Party Barge quest, I decided to use the Fulminate Horn to deal with the swarm of ships that would pile up for fun. Well, upon using the ship power, it puffs out smoke, lightning strikes, but no damage is inflicted on the ship or ships. Not even a miss that normally pops out if your attack doesn't land. I thought this was only for the Cutthroat ships, so I tried it on the Armada ships nearby, and the same thing happened. It doesn't do any damage to them at all.
I guess I'm not too surprised this bug went unnoticed as it's a pretty hard drop to get, and usually you're at a disadvantage if you try to fight several ships alone.