You need to know 4 or 5 things usually...

1. Ship speed, hardness/armour, size
2. Weapon Range & Damage
3. Adjusted Attack Rolls for Cannon-Like devices
4. Weather/Conditional Modifiers (e.g. a moderately moving ship would probably reduce the effective range of a bow/spear by a range increment)
5. Wind effects on projectiles (e.g. a very strong wind would probably reduce effective range of all weapons by 3 range increments or more)

That should point you out to find what you need to know. I'd be suggesting that purely magical attacks would ignore conditions, but cause problems for casting (% fail chances or similar)