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GURPS/Naval Combat

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This is a set of rules for playing out combat situations among naval vessels. Unlike characters, ships can vary wildly in resistance, speed and power, and a naval combat can be decided very swiftly if the difference between vessels is too big.

A ship’s attributesEdit

Like characters, a ship has attributes which influence its combat performance. Most of these are very much known, others are specific to vessels:


The average skill level in “sailor” of the ship’s sailors. This influences all rolls and is the base attribute against which a vessel rolls to all of its actions. Specific skills possessed by the ship’s officers are accounted for through the “Expertise” attribute.
For instance, a ship’s gunner has his “Gunnery” skill at level “IQ+2”. When rolling to fire, the roll is made at the ships “Expertise+2”. The gunner’s skill is actually performed by the sailors, and he only coordinates their action.
A ship is only as good as its sailors. Veteran sailors are a boon to any vessel, but they also cost more to maintain.


How much hexes a ship can move in one turn. Each hex in a naval combat map is considerably greater than the usual "1m radius" of tactical combat hexes. In general, a ship always occupies 2 hexes on the map, and has a movement in hexes which equals its nominal speed (in kph) divided by 7. This doesn’t mean that the ship’s size actually occupies 2 hexes, but this is a ship’s range when it comes to close combat.
Ships whose move is less than 7 kph can still move, but they must take note of their move in fractions: 1/2, 1/3, 1/4 and so on. This means the ship moves 1 hex each 2 turns, or each 3 turns, etc.
Round the ship’s move to the nearest integer or the nearest "simple" faction (a fraction whose denominator is an integer less than 10). Ships that move less then 1/10 do not move on combat. For clarifiation:
 If the speed is between   and   then Move is 
 24,5   31,5   4 
 17,5   24,5   3 
 10,5   17,5   2 
 5,25   10,5   1 
 2,916666667   5,25   1/2 
 2,041666667   2,916666667   1/3 
 1,575   2,041666667   1/4 
 1,283333333   1,575   1/5 
 1,083333333   1,283333333   1/6 
 0,9375   1,083333333   1/7 
 0,826388889   0,9375   1/8 
 0,738888889   0,826388889   1/9 
 0   0,738888889   1/10 


The ship’s DR. A ship’s entire DR is ablative: for every 5 damage points that go through DR, reduce HP by that amount AND reduce 1 point of DR.


The ship’s structural hit points.


This is how much damage each one of the ship’s cannons can cause. A 100mmm breechloader cannon causes 5dx10.


Most cannon damage is pretty high, as well as ship’s HP (a basic ship can have 40000 points of HP). To facilitate calculus, a ship’s damage, HP and DR is divided by a power of 10 when calculating attack. This is a ship’s “Scale”. Nearly all ship’s scales are 10, but huge ships can have a greater scale.

Num of CannonsEdit

How much cannons there are in each side of he ship, and on the front. It is noted as four numbers: Left, Right, Front and Back. For instance: A ship with: 10/10/4/3 would have 27 cannons, 10 to either side, 4 to the front and 3 to the back.
When rolling for damage, multiply the damage of the ship by the number of cannons that fired. ALSO multiply the target ship’s DR by the same amount, and only then account for damage.


The range of a ship’s weapons in hexes. This is usually 5.


It takes 1 turn of combat to reload a cannon. It takes 2 crew members to reload 1 cannon. So, for instance, if a ship has 10 cannons on its left and right, it could reload one of its sides in a turn. However, while doing that, it could not also fire the rest of the ship’s cannons.

Size ModifierEdit

A ship’s size modifier greatly influences combat. All attack rolls between ships are modified by the difference in size modifiers. A size +5 ship attacking a size +3 one has a -2 penalty in all of its attack rolls, and the +3 ship has a +2 bonus in all of its attack rolls.


This is the number of crewmembers in a ship. There are “crew” and “skeleton crew” values. “Crew” is the ship’s actual number of crewmembers. “Skeleton crew” is a number which the ship’s crew cannot go below, or the ship will not be able to move or attack in a given turn. If a ship’s crew equals its “skeleton crew”, it can only move at half move, OR attack in a given turn (not both).

Officer AttributesEdit

A ship’s leaders can influence combat, for better or worse.

Leadership (IQ/A)Edit

The ship’s commander relative skill level in Leadership is the greatest bonus that each other officer can grant to its rolls. A commander whose leadership is “IQ+2” has a leadership of “+2”. No other officer can grant a bonus to the ship’s rolls that’s greater then +2. A ship’s commander can also perform another of the roles below, if his skill level in one of the skills below is good enough.
If no commander is present in a vessel, then the default gunner level is -5.

Gunnery (IQ/A)Edit

The gunner’s ability to attack enemy ships. The basic attack roll of a ship is: “Expertise”+”Gunnery”.
If no gunner is present in a vessel, then the default gunner level is -5.

Navigation (IQ/A)Edit

A good navigator knows how to use wind to his favor, and how to best make use of a ship’s sails. A ship moves a number of hexes per turn which equals its speed / 20, plus 1 hex per relative skill level in “Navigation”. If the relative skill level in navigation is below IQ, then the ship’s navigator ability diminishes the vessel’s performance.
If no navigator is present in a vessel, then the default navigator level is -5. If a ship’s “navigation” takes its move to 0, then the actual move is 1/2. If it’s -1, then the actual move is 1/3. If it’s -2, then the actual move is 1/4, and so on.

First-Aid (IQ/H)Edit

On-demand patch jobs can get a crew working during a crisis. If a ship has a surgeon, he can prevent 1 crewmember from going out of combat, per turn, per relative skill level of “Surgery”. A surgeon can instead choose to use its relative skill level bonus to prevent one crewmember from dying, per point of level, per turn.
Healing Spells in naval combat
If a ship has a mage with healing spell capability, he can prevent crew loss in addition to what a surgeon can. This is even true if the surgeon is the mage himself.
Calculate how many healing spells the mage is able to cast at full strength. These spells cost 4 energy points, and thus this number equals the mage’s fatigue points divided by 4 (plus any powerstones, if he wants to use them).
This is a number of crewmembers that he can save during a combat, one time only. However, these crewmembers can be brought from “dying” to “combat-ready” in the same turn.
For instance, if a mage has 15 fatigue points, he can cast 3 healing spells at full power. This means that 3 times during the combat, he can prevent one crewmember from dying and fully recover him, allowing him to continue acting on the next combat turns.

Tactician (IQ/H)Edit

An officer with “naval strategy” can add their relative skill level to all boarding rolls made by his ship’s crew. He can also use his positive bonuses outside of boarding actions: he can increase any other officer’s bonuses using his own. A tactician with “Strategy (naval)” at IQ+2 could, for instance, add +1 to navigation and +1 to gunnery for the combat. He can shift his bonuses as he sees fit on every turn.

Naval Combat MechanicsEdit

Like tactical combat, naval combat is resolved in turns. Before any action takes place, initiative is rolled.

Initiative rollEdit

All naval combatants roll 1 die and add to it their ship’s movement (modified by the ship’s navigator). This is their initiative value for the combat. As a ship loses movement during combat, its place in the initiative scale will also change.
Ties are resolved by the greatest navigation bonus of a ship. If these also match, then the players go first.
A turn of naval combat is resolved by going through every ship in their initiative order. The actions that a vessel can perform in its turn are “move” and “attack”. However, a vessel can do both of these if its crew allows. Whether it attacks before it moves or it moves before it attacks, or attack while it moves, is up to the controlling player.

Vessel MovementEdit

A vessel can move up to its “move” +”navigation” per turn. Whenever it moves, it can also turn, but a ship can only turn if it also moves.
If a vessel is going to turn, it must move first and turn later. The correct way to go about this is “move->turn”, and not “turn->move”. Each hex of movement allows for 60 degrees of turn in any one direction.
A ship turns relative to its back hex. Ships occupy 2 hexes on the map: when a ship turns, the back hexagon does not change, and the front hex is the one that turns.


A ship can not attack with all of its cannons at once, only cannons that are facing an enemy. Cannons placed at the side have a 60-degree arc of fire, while cannons placed at the front or back have a 30-degree arc of fire. There are always some “blind spots” in a ship’s attack arc.
When a ship is going to attack, it rolls its “Expertise” modified by Gunner level, if any. If no gunner is present, then the default gunner level is -5. Also modify this roll by the difference in size modifiers between the opposing ships.
There are no “active defenses” against a ship’s attack. If the roll succeeds, then the opposing ship takes damage. If the roll misses, the opposing ship STILL takes damage, but only half.

Interrupted attacksEdit

If a ship has its cannons at the ready, enough crew to man the cannons, and an opponent moves through its range of attack in its turn, then the ship can perform an attack in the opponent’s turn. This is resolved as a normal attack.
When two ships move in range of each other and both are ready to fire, they can both do. However, in this case, resolve the attack of the ship whose turn it is first, and then move on to the attack of the ship which interrupted the other’s movement.
After an interrupted attack takes place, the ship of the turn can continue with its movement, if it has any.


In order to get a ship to attack, its cannons must be loaded. After an attack takes place, they have to be reloaded, and until that happens, those cannons can no longer fire.
2 crewmembers are necessary to fire and to reload a cannon. If a ship has twice its number of cannons in crewmembers, then it can reload those that fired while others are still attacking. Otherwise, the crew has to be split in order to perform one or another action, as the commander sees fit.


Damage to a ship has three consequences: structural damage, crew damage and mast damage.

Structural damageEdit

Structural damage is resolved as noted. The attacker rolls its cannon damage times the number of cannons that fired. Enemy DR is multiplied by the number of cannons that fired. Excess damage reduces the ship’s HP. If a ship’s HP drops to 0, it sinks.
If a ship’s HP drops to half its usual level, the ship loses 1 movement point. If it drops to one third, the ship loses 2 movement points. If it drops to one fifth, the ship loses 3 movement points. This affects the ship’s initiative.

Crew damageEdit

Every 20 full points of damage that a ship takes reduces its crew in 1. This is crew damage. When crew is damaged, half of the crew losses (round down) are deaths, and these crewmembers are gone. The other half are wounded and will need surgery to return to action (the kind of which takes a recovery time longer than the combat’s duration). A ship’s surgeon can use his “First Aid” relative skill level to prevent crew from going out of combat OR to prevent crew from dying, as he chooses.
For instance, if a ship takes 100 points of damage, 5 crewmembers will go out of combat: 2 dead and 3 injured. If the ship’s medic has First Aid in level IQ+2, he could prevent the 2 deaths, though all 5 would be injured, or he could accept the 2 deaths and prevent 2 injured from going out of combat on that turn. He could even split his bonus to prevent 1 death and 1 injured.

Mast damageEdit

Every 100 full points of damage that a ship takes reduces its speed in 1. If a ship’s base speed (without being modified by the navigator’s relative skill level) drops to 1/10, then the ship lost its masts and cannot move any further.
A ship’s navigator can prevent damage to the masts. He can forfeit 1 of his bonus points from his navigation skill and prevent the loss of 1 point of movement. That effectively decreases the ship’s movement and initiative standing for 1 turn of combat. A navigator can only use his positive relative skill points in that manner.


If a ship moves head-first into another’s hex, it rams into the opponent. Ramming causes a brutal damage to a ship’s hull and also damages the attacker.
The attacker damages the target for a number of hit points which equal the attacker’s DR plus the number of hexes it moved in a straight line, times 100.
Ramming damage = (Attacker’s DR + moved hexes) * 100
The attacker also takes a number of points of damage which equal the target’s DR plus the number of hexes it (the attacker) moved in a straight line, times 20
Ramming collateral damage = (Target’s DR + moved hexes) * 20
This damage is modified by the ship’s scale, if they differ. Otherwise, it happens on the ship’s scale (i.e., if the ship’s scales is 10, divide these damages by 10).
Ramming damage does not reduce crew or mast.
After a successful ram, either the target or the attacker can start a boarding action.


When two ships pass side by side, or when one rams the other, either one of them can start a boarding action. The ship’s crew takes up arms and tries to take control of the other ship by force.
When boarding, none of the ships can move. One of them can attempt to disengage from the boarding, but that will give it a -3 penalty in their boarding roll on that turn. The ships can still fire their cannons at each other, if they have crew to do so and cannons at the ready.
On a boarding, both ships roll their “Expertise” + “Tactician” level. The margin of successes of this roll is added to the damage that each crew causes each other. Each crew causes a number of points of damage to the other which equal one fifth its number of active crew members, plus the margin of successes on the boarding contest, plus the highest damage modifier of the weapons they are using. The result number is a damage to the enemies’ crew.
Boarding roll: Expertise + Tactician relative skill level
Boarding damage: (Crew / 5) + Weapon damage modifier + Boarding contest margin of successes (if positive)
Only add the results of the boarding contest to the victor’s damage.
Crew lost during a boarding follows the same rule as for normal naval damage: Half is dead, half is injured and may recover with surgery. A ship’s surgeon can change that normally (and thus, prevent crew loss during a boarding).

Boarding ExampleEdit

The crew from “Jahara’s Jewel” is boarding “Kartazian Sun”. Jahara’s Jewel is using 50 crew members all armed with knives (for -1 damage). It has a Tactician of skill level IQ+3, and the crew’s expertise is 12.
The “Kartazian Sun” is defending with 30 crew members armed with swords (for +2 damage). Its tactician has skill level IQ+2 and crew expertise is 14.
Turn 1: Jahara’s Jewel rolls 9 against a total of 15 (12+3). Kartazian Sun rolls an 8 against a total of 16 (14+2). The margin of successes is 2 in favor of Kartazian sun.
Jahara’s Jewel damage is 1/5 its crew (10), plus weapon damage (-1): 9 crew members. Kartazian Sun’s damage is 1/5 of its crew (6), plus weapon damage (+2), plus the margin of successes (+2): 10 crew members.
Turn 2: Jahara’s Jewel rolls 12 against its total of 15. Kartazian Sun rolls a 10 against its total of 16. The margin of successes is 3 in favor of Kartazian sun.
Jahara’s Jewel crew is now 40. Its damage is 1/5 its crew (8), plus weapon damage (-1): 7 crew members. Kartazian Sun’s crew is now 21. Its damage is 1/5 of its crew (4), plus weapon damage (+2), plus the margin of successes (+3): 9 crew members.
Turn 3: Jahara’s Jewel rolls 7 against its total of 15. Kartazian Sun rolls an 11 against its total of 16. The margin of successes is 3 in favor of Jahara’s Jewel.
Jahara’s Jewel crew is now 31. Its damage is 1/5 its crew (6), plus weapon damage (-1) , plus the margin of successes (+3): 8 crew members. Kartazian Sun’s crew is now 14. Its damage is 1/5 of its crew (3), plus weapon damage (+2): 5 crew members.
Turn 4: Jahara’s Jewel rolls 10 against its total of 15. Kartazian Sun rolls a 4 against its total of 16. The margin of successes is 7 in favor of Kartazian Sun.
Jahara’s Jewel crew is now 26. Its damage is 1/5 its crew (5), plus weapon damage (-1): 4 crew members. Kartazian Sun’s crew is now 6. Its damage is 1/5 of its crew (1), plus weapon damage (+2) , plus the margin of successes (+7): 10 crew members.
The Kartazian Sun`s tripulation, in spite of its efforts, was reduced to 2 crewmembers. Against Jahara`s jewel`s 16, they see no option but to surrender.

Player actions during a boardingEdit

Player characters can enter a boarding action and usually tip the scale in their favor. When players enter the fray, their actions are resolved separately then the boarding roll. The enemies that they face are removed from the enemies’ boarding crew, and a secondary combat takes place, along with the main boarding actions.
At every turn, the number of enemy sailors that the players face may change according to how many enemies choose to attack them. This can greatly alleviate the pressure that their own forces face, especially because one player can usually take care of more than one enemy at a time.
Every turn of boarding is 3 turns of combat for the players.

Sample ShipsEdit

These ships were built using GURPS Vehicles for the Third edition, and converted for use with these rules. They are all TL5 ships:

 Name   Sloop   Schooner   Tern Schooner   4-Mast Schooner   Brigantine   Brig   Barquentine   70-gun military 
 Scale   10   10   10   10   10   10   10   10 
 Top Speed   12.9 kph   16,1 kph   16,1 kph   19,3 kph   16,1 kph   17,7 kph   14,5 kph   14,5 
 Move   2   2   2   3   2   3   2   2 
 DR   1   2   2   2   2   3   3   5 
 HP   450   900   900   900   900   900   1120   1870 
 Damage   5d   5d   5d   5d   5d   5d   5d   5d 
 Cannons   4/4/0/0   5/5/0/0   5/5/2/2   6/6/4/4   6/6/4/4   7/7/1/0   15/15/5/5   30/30/5/5 
 Range   5   5   5   5   5   5   6   6 
 Size Modifier   +8   +8   +8   +8   +8   +8   +8   +8 
 Crew   8   10   21   27   28   23   132   701 
 Skeleton Crew   4   5   5   5   6   6   8   50 
 Ship Weight   132 tons   236 tons   294 tons   365 tons   306 tons   358 tons   623 tons   1437 tons 
 Ship Price   $181075   $267450   $354925   $466600   $374400   $387400   $661150   $1616150 

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