I wouldn't like to guess. But it's something I'd guess they've balanced out.

Would it be worth trying to make some house rules for chain shot. If aiming for sails/masts flip a coin (maybe per gun section? Eg 3 flips for a broadside; front, middle, rear) to see if you deal any sail damage - if yes take how ever many damaged sail counters. If you're aiming for the hull, take an agreed amount of damage counters. That sounds fair.