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Naval Combat

by Donald Eric Kesler

The following rules are not new rules. They are simply old rules that have been organised in a more logical manner. I found it necessary to do this for my campaign after the player characters acquired a particularly potent war ship. The rules presented here originally appeared in the Rules Cyclopedia, Gazetteer 4: The Kingdom of Ierendi and The Champions of Mystara.

Evasion at Sea

Ships meeting at sea may wish to evade one another. To determine one ship’s chance of eluding another ship, consult the Ship Evasion Table.

Ship Evasion Table

Evading Ship’s Speed (per round) Chance of Evasion
Faster than pursuer 80%
0’-30’ slower 50%
31’-60’ slower 40%
61’-90’ slower 35%
91’-120’ slower 25%
121’ + slower 10%

If evasion is successful, the pursuer loses sight of its prey and cannot find it again or attack it that day. A ship can evade its pursuer by sailing into a baffling archipelago, heading into a concealing fog, hiding itself in a cove and ducking out once the pursuers are past, and so forth.

If the evasion is not successful, the pursuer starts at a distance of 300 yards on a clear day. (At the DM’s discretion, if the weather is impairing vision, the pursuer may start closer.) The pursuing ship closes in.

If the pursuer’s speed is 0’-30’ per round greater than the evader (or actually slower), the rate of closing is 10 yards per round. If the difference is greater than 30’ per round, the pursuer closes at its normal movement rate.

A slower vessel can close on a faster vessel by virtue of superior sailing. If the evading sip missed its roll for evasion on the Ship Evasion Table yet it is faster than the pursuing ship, this means that the pursuer is sailing much more effectively than the evader.

If the DM is using the optional general skills rules, he or she can roll the two captains’ Piloting skills in competition with one another. If the evading ship’s captain rolls his skill better, he evades pursuit; if the pursuer rolls his skill better, he is able to close at the rates described above (RC 100).


Galleys, armoured fireships, and long-ships move any number of hexes up to their full speed. They rely on a combination of oar, and sails and/ or magical technology.

Sail ships move from half their movement rate (rounded up) to full speed because they rely on the winds. A sail ship cannot stop, unless it collides with another ship (GAZ4 30).

Manoeuvring Factor*

Manoeuvring factor measures how manoeuvrable a [sailing ship, sea monster,] skyship or flying creature is. It determines the number of times each round a vessel can perform a manoeuvre, a change up to 60 degrees in horizontal or vertical direction.

To determine the vessel’s Manoeuvring Factor, compare her length in feet from bow to stern, or along her longest axis (excluding any accoutrements such as masts to the Manoeuvring Factors chart. If the vessel is aerodynamic, use the middle column; use the right hand column for non-aerodynamic craft.

Manoeuvring Factors chart

Ship’s Length Aerodynamic Not Aerodynamic
To 2’ 5 3
To 10’ 3 1
To 50’ 1 1/2
To 250’ 1/2 1/3
To 1250’ 1/3 1/5
1251+ 1/5 1/10

Magical Motive Power: Ships moved by magic are treated as one category better on the chart.

Flying [& Swimming] Monsters: Vessels using flying [and swimming] monsters as their Motive Power must take the monsters’ Manoeuvring Factor into account as well as the ship’s.

To find the monster’s Manoeuvring Factor, find its length (or height if it’s taller than long) on the chart. A pegasus [or dolphin], for instance, would fall on the “To 10” line.

Most monsters are aerodynamic. A monster may belong to the non-aerodynamic line if it floats rather than flies [or swims] or if it has a maximum flying [or swimming] speed of 30’ or less per round. [Regarding aerial Manoeuvring Factor,] [m]onsters related to the plane of Air (djinni, for example) or that are nimble in flight (dragons, etc.) rate one category better on the chart. [Likewise, when dealing with aquatic encounters, monsters related to the plane of water (undines, for example) or that are nimble swimmers (sea dragons, etc.) rate one category better on the chart.]

The Manoeuvring Factor of a vessel drawn by flying [or swimming] monsters is the worst of the following; the vessels normal Manoeuvring Factor (based on size alone), one category lower than the monsters’ Manoeuvring Factor (if the vessel is aerodynamic), or two categories lower than the monsters’ Manoeuvring Factor (if the vessel is not aerodynamic). Use the worst monster Manoeuvring Factor if more than one monster is involved (CoM 11)


A manoeuvre is a change in direction by 30 or 60 degrees. On hex paper, 30 degrees changes a skyship’s [or sailing ship] direction from the centre of one hex face to an adjacent vertex or vice versa; 60 degrees changes a skyship’s [or sailing ship] direction from the centre of one hex face to the centre of an adjacent hex face, or from one hex vertex to an adjacent vertex. Changes in altitude, both climbing and diving, are also manoeuvres, see below.

Continuing an old manoeuvre is not the same as starting a new manoeuvre. Beginning a climb counts as a manoeuvre – continuing the climb in the next round does not. Levelling off to horizontal flight does count as a new manoeuvre.

The first manoeuvre performed in any round is “free” – if the pilot is conscious and the vessel or monster is responsive, the manoeuvre automatically succeeds. The following require a skill check against Piloting or another skill:

· This is the second or subsequent manoeuvre by that vessel or monster in the same round. (This only pertains to monsters or vessels with more than one manoeuvre per round.)

· The pilot, who controls the vessel’s manoeuvres, lost one tenth of his hit point total (or the vessel lost one tenth of her hull points) in the last round.

· The pilot has taken one half of his total hit points or the vessel has lost of half of her total hit points.

· Any flying or flightless creature providing Motive Power have taken half their total hit points, or half or more of the creatures were damaged last round.

· Any circumstance the DM thinks would make manoeuvring difficult – heavy rains or winds, poor visibility, etc. – should also require a check (CoM 23).

Naval Combat

Naval combat between water vessels usually starts with missile fire and magic. When the boats are close enough, the enemy craft is grappled and boarded, and hand-to-hand combat takes place between the two crews. A ship with a ram can do special damage to other ships and large monsters.

Unless noted otherwise, giant sea creatures and magic attacks inflict 1 point of hull damage for every 5 points of normal damage (RC 115).

Missile Combat

The armour class of the ship is the number used to determine chances of success for ram and catapult attacks against a ship (RC 71).

Crews of ships can fire upon one another whenever they come within missile range. Ships armed with catapults will tend to be more effective than those without. Hand missile weapons such as bows and crossbows can damage and kill crewmen, but do no effective damage against the ship itself. A catapult, on the other hand, does its full damage to either ship or living target (RC 115).

Magical Attacks

Most magical attacks do only 1 point of hull damage for every 5 points of normal damage. The attack may have other effects, however.

Fireball and Other Magical Flame Attacks: Wooden- and cloth-framed vessels are susceptible fire unless they have been protected against it. When a fireball or similar magical attack hits, roll d% and compare the result to the total number of hit points damage the attack did (before dividing by five). If the d% roll is greater than the number of hit points of damage, the vessel’s frame does not catch fire. If the roll fails, the hull catches fire, taking 1d4 hull points until the fire is put out.

Other Magical Attacks: DMs may need to use some imagination (mixed with common sense) to determine the effects of other magical attacks on flying [and sailing] vessel[s]. For instance, a clerical barrier spell cast suddenly in a wooden skyship’s [or sailing ship’s] path can be devastating. The spell’s whirling hammers can destroy the results of a woodform spell; a barrier spell will do 5 hull points of damage for every 5 normal points of damage.

The druidic turn wood spell could force a wooden-hulled skyship [or sailing ship] from her course, perhaps pushing her into the ground (at 10 yards per round, not enough to do much damage) and pinning her there for a while (CoM 26).


Wooden structures can be damaged by fire, but take only 1 point per 6-sided die of damage or per 5 points of maximum possible damage, rounded up.

Furthermore, wooden items attacked by fire can be set afire, causing further damage. The chance of being set afire is 5% per point of damage caused by each fire attack. Anything set afire will take 1 point of damage the first round, 3 more points by the end of the first turn, 6 points the second turn and 12 points for each turn thereafter, until destroyed.

Any creature caught within a burning structure will take damage equal to 1d6 per point of structural damage at the same rate. Any flammable structures next to the structure that has been set afire may also catch fire with a chance of +10% for each turn the first structure burns.

If water or loose earth and workers are available, the workers may attempt to extinguish the fire. Each turn a fire is fought, the player should roll 1d6 per 10 workers. This is the number of points of structural fire damage extinguished that turn. If the number is greater than the fire damage for that turn, the fire is extinguished. Only ten people may fight a fire for each thirty feet of structural damage. Each fire fighter suffers 1 point of damage per point of structural damage caused for that turn. If the fire was caused by special catapult shot or a dragon, fire fighters can extinguish only half the normal number of points.

Stone will not burn, but wooden parts of stone constructions will burn (roofs, floors, doors, etc.) fire damage is the same as for wooden structures, but only 10% of the total hit points of a stone building may be burned (RC 116).

Close-Quarters Combat

When ships come close to another, they normally try to ram or board one another.


To ram a target, the ship must bring its bow into contact with the enemy ship – in other words, it must close until it touches the enemy ship. Ships can also ram large sea-monsters. Small targets are impossible to hit with a ship. They can easily outmanoeuvre a ramming vessel.

The ram attack takes place in the missile phase of the combat round in which the ships touch. The ramming ship’s pilot rolls to hit as if he were a 1st level fight attacking the target ship’s armour class. The DM can modify this for weather conditions, manoeuvrability, and other factors. The ram, if it hits, does damage to the ship’s hull points (or if it hits a large sea creature, to the creature’s hit points).

Each successful ram attack does damage according to the size of the ramming vessel as shown on the Ram Attacks Table.

Ram Attacks Table

Ramming Vessel Opponent Damage
Small Galley Ship 1d4+1x10 (50-80)
  Creature 3d8 (3-24)
Large/War Galley Ship 1d6+5x10 (60-110)
  Creature 6d6 (6-36)

On the same round the attacker has rammed the defender; it may decide to grapple during the hand-to-hand phase of the combat round. If its crew does successfully grapple, they can begin to board on the next combat round’s movement phase.

Grappling and Boarding

Ships’ crews attempt to grapple at a distance of 50’ or less. If both ships’ crews want to grapple, grappling is automatically successful. Both crews throw out their grappling lines, both sets of lines connect, and the ships are drawn together. If only one ship’s crew wants to grapple, roll 1d6 every round; a result of 1-2 indicates success while a 3-6 means that the other crew successfully cuts and casts the grappling lines free.

After the ships are grappled, the boarding battle is fought just like any other large hand-to-hand combat. Characters boarding an enemy vessel have a penalty of +2 on armour class and -2 on all attack rolls during the combat round they board; the difficulty of climbing over two sets of ship’s rails and finding footing on an enemy deck puts them at risk. The battle continues until the crew of one ship surrenders or dies.

Damage to Ships

A ship’s ability to remain afloat after taking water or damage is measured by a number called hull points. Hull points for a ship are very similar to hit points for a character; when a ship reaches zero or fewer hull points, it will sink in 1d10 rounds (RC 71).

Each 10% of hull damage reduces the ship’s speed by 10%, until the ship is repaired in port. Each 10% loss of rowers reduces a ship’s rowed speed by 10% also. When the ship has suffered 75% of its hull points in damage, the ship is dead in the water; it cannot move until at least makeshift repairs are made. When the ship has taken all its hull points in damage, it sinks, and repairs are no longer possible (RC 115).

If a ship is reduced to zero or fewer hull points, it can no longer move under its own power or attack with ship-mounted weapons. The DM can decide whether any onboard catapults are then destroyed ( he can choose to roll 1d6, with a 1-4 indicating that the weapon is wrecked); the crew may use personal weapons normally (RC 71).


A ship’s crew may repair up to half the damage the ship has taken. Five or more crewmen must be assigned to repair duty for repairs to be effective. A repair crew can repair one point of hull damage per full turn of work. These repairs are makeshift and will fall apart in 6d6 days; for permanent repairs, and to get the remaining hull points repaired, the crew must get the ship to a port.

Repairs and attempts to put out fires take place after the ship sustains its damage for the turn. Repair and fire crews cannot fight or do anything else while performing these tasks (RC 115).

Permanently repairing damage requires 1/3 day in dock and 150 gold pieces per hull point of damage being repaired. A carpenter needs to be on hand to supervise repairs. If the ship has sustained a loss of more than 50% of its hull points, a shipbuilder or an engineer will also need to also be employed in order to affect repairs (GAZ4 35).

*I apologise if the section on Manoeuvring Factor is confusing. I will admit it could be more elegant, but I wanted to keep as much of the original language intact as possible. The CoM was a set of rules designed to work with flying vessels. I have adapted these rules to work with aquatic vessels.

Gazetteer #. Series of books describing the countries of the KW (OD&D).
Rules Cyclopedia. Compilation of the old rules, with Mystara extension (OD&D).
Champions of Mystara. Campaign extension describing the area between the KW and the SC, and skyships (OD&D).