Could you provide your final set of rules? If not, I have access to those rules and will cobble it together.
Either way, thanks for the ideas.
Can do.
Introduction
Understand that by default 3.5 rules, ship to ship combat is all about "holing" sections of a ship, so the captain is forced to make a sinking check. Larger vessels have more sections, and so you'd need to hole more sections to make it sink. Also, depending on the size of the ship, the ship will have a limited number of weapon mounts, which determine how many cannons/ballistas/catapults the ship can have. But if you want to play out a battle between many ships, it takes way too long to roll all those attacks and track all those sections. The battle would take forever and be really, really boring. My homebrew rules simplify these elements into general stats, so that each ship has only one health pool and one attack (which is based on their original stats). No sinking checks or holing of sections. These rules can also be applied to seamonsters. Just treat them as a ship.
CR (Challenge rating)
This mechanic is borrowed straight from Pathfinder's Mass Combat (in which it is called ACR). It uses the character level of an average crew member on the ship and the total size of the ship's crew, to come up with a rating that determine's the overal strength of the ship's crew as a single unit.
| Crew Size | Number of Units | CR |
| Fine | 1 | CR of individual creature –8 |
| Diminutive | 10 | CR of individual creature –6 |
| Tiny | 25 | CR of individual creature –4 |
| Small | 50 | CR of individual creature –2 |
| Medium | 100 | CR of individual creature |
| Large | 200 | CR of individual creature +2 |
| Huge | 500 | CR of individual creature +4 |
| Gargantuan | 1,000 | CR of individual creature +6 |
| Colossal | 2,000 | CR of individual creature +8 |
Hitpoints
The hitpoints of the ship and its crew are basically one and the same in this system. A ship's HP equal its CR × the average hp value of 1 HD of the ship’s crew (3.5 for d6 HD, 4.5 for d8 HD, 5.5 for d10 HD, and 6.5 for d12 HD). Note that only damage from other ships (and seamonsters that are treated as ships) can reduce a ship’s hp; a non-ship attacking a ship is mostly ineffective, though you can treat the attacker as a Fine Unit if you want to determine the outcome of the attack. As with standard effects that affect hit points, abilities that reduce hp damage or healing by half (or any other fraction) have a minimum of 1 rather than 0.
Defense
CR + 10 + any bonuses from ship upgrades and/or special effects.
Attack
Added to D20 attack rolls. Equal to CR + the arms of the ship.
Add +1 for each light weapon mount, and +2 for each heavy weapon mount.
Attack rounds
Each ship deals damage by rolling D20+the ship's attack, minus the target ship's defense. If the result is more than 0, the ship deals the difference in damage+any damage modifiers. If the result is 0 or less, the ship deals no damage at all. Natural 20's are ignored, but on a 1 the ship will not be able to attack in the next round (due to some setback, misheard order, etc). All of the attacks take place simultaneously, which means two ships might destroy each other during the same round.
Morale
This number represents how confident the crew of the ship is. Morale is used to determine changing battle tactics, whether or not a ship routs as a result of a devastating attack, and similar effects. Morale is a modifier from —4 (worst) to +4 (best). A ship’s starting morale is +0. Morale can be further modified by the captain and other factors. If a ship's Morale is ever reduced to —5 or lower, the ship flees and you no longer control it. The DM can decide which events affect morale. Seeing an allied ship get destroyed may lower morale, while defeating an enemy ship may increase it. Seeing a seamonster rise from the depths may lower morale too (or seeing any monster with a frightful presence).
Rout
A rout is a chaotic and disorderly retreat of a ship, usually from fear or when overwhelmed by a superior opponent. If a ship’s hit points are reduced to
equal or less than its CR, its captain must attempt a
DC 15 Morale check. If the check fails, the ship retreats from battle. If it cannot retreat, it surrenders and is captured. When a ship routs, all ships in the battle can attempt one final Offense check at the fleeing ship as a parting shot before it escapes. (Normally, only enemy ships do so, but an aggressive or evil fleet might strike at a fleeing allied ship out of anger or frustration.)
Strategy
On the first phase of combat, the ship's captain selects a strategy from one of five options on the strategy track. Strategies adjust the ship’s defense, attack, and damage modifier. Once each Combat phase after the first, the captain may alter the ship’s strategy. Adjusting the strategy 1 step up or down is automatically successful and doesn't require a check. If the captain wants to adjust the strategy more than 1 step, the ship attempts a
DC 20 Morale check. Success means the strategy changes to the desired level. Otherwise, the ship’s current strategy doesn't change.
| Strategy | Damage | Attack | Defense |
| Defensive | -6 | -4 | +4 |
| Cautious | -3 | -2 | +2 |
| Standard | +0 | +0 | +0 |
| Aggressive | +3 | +2 | -2 |
| Reckless | +6 | +4 | -4 |
Maneuvres
For special maneuvres the rules from Stormwrack are used, which usually use the captain's profession (sailor) skill.
Special ship qualities
This is where the DM can add special qualities/upgrades of the ship (or sea monster). These are innate qualities that a ship may already have.
A few examples:
Ship of the line: +2 on defense
Ghostship: 50% miss chance, +2 to the DC of enemy morale checks, can board on a ramming attack.
Harpoon attack: Can grapple ships with a ranged attack.
Submersible: Underwater movement is only visible from the air or below sea level.
Ram: +4 on ramming attacks and damage.
Armored +2 on defense.
Mines: Can lay naval mines once. (Mine impacts count as attacks)
Kooghan Firepower: +2 to attack, due to special cannons.
Kooghan Superstition: The crew is more susceptible to fear from the supernatural.
Opportunist: +2 on raking attacks and damage against bow or stern.
Close-hauled: Can sail against the wind.
Necromancy: +2 to attack when boarding, and can turn a captured vessel into a fully crewed allied vessel.
Cruelty: Will pursue fleeing ships.
Scrying: Can scry on enemy vessel.
Fireships: Can unleash Fireships and obscure the battlefield with chemical clouds.
Nightmarish Visions: +2 to the DC of opponent's morale checks through the use of illusions.
In conclusion
If this seems like a lot to take in, understand that most of this is merely preparation. During an actual session, combat flows quite quick with this system, because it eliminates a lot of dice rolls, without ignoring the qualities that make certain ships unique. I created small stat blocks for each ship, and pasted them on cardboard, so my players could easily keep track of their entire fleet. The players do not need to understand the system, they just need to know what to add to their rolls.
