Ship Cannons in Lamentations of the Flame Princess

Note: I am basing this very heavily on a combination of rough estimates, Wikipedia, The Sealed Knot, and some helpful forum posts by other LotFP players.

As they soon plan to acquire a ship, my Lamentations of the Flame Princess group has raised questions about ship cannons. Although Rules & Magic includes rules for ships and ship combat, the latter only uses catapults and the like, not modern gunpowder weapons, and it would be faintly ridiculous in 1643 for my player characters to sail along in a galleon armed with catapults.

I have been asked how many cannons can the ship types in the Rules & Magic book carry, what types, how much do they cost, etc. The only real rules for cannons in Rules & Magic are the rules for “artillery” in the gunpowder appendix. Rather than provide a list of discrete types of artillery, artillery is an abstraction which scales up damage, size, and cost as you buy bigger and bigger pieces of artillery. That’s fine, but means that you can’t simply take a list of historical ship armaments and directly obtain the game stats for them.

For that matter, historical ship armaments, like other ship stats, were extraordinarily variable. There was no “standard” armament for a galleon or a frigate or any other ship type on the list in Rules & Magic. In the early modern era, warships were loaded with as many cannon as they could carry whilst remaining upright. In a few famous cases (e.g. the Vasa), warships were so overloaded that remaining upright proved impossible. With that as a disclaimer, we can still use historical ship armaments to get a vague idea of what a ship of each type could conceivably carry. We can also use the cargo capacity of a ship to estimate how many cannons and barrels of gunpowder it can carry, since a ship is essentially trading cargo space to carry weapons.

The problem is that LotFP uses an abstract encumbrance system for determining how much a person or a horse can carry, but ships carry cargo in tons. Rules & Magic specifies that each size category of artillery translates to 25 Encumbrance Points. Since my campaign is set in the English Civil War, what better resource to use than the Sealed Knot’s website to look at artillery size? Of these, the smallest two are too light to correspond to even the first size category of artillery in LotFP rules terms – since it takes 2 horses to comfortably pull the falcon, this is a good place to start as the “size category I” cannon. The LotFP forum posters probably came to a similar conclusion since “Falcon” is listed as the Size Category I cannon. The weight of a Falcon is estimated at 700lbs. An Imperial Ton is 2240lbs, so we could roughly say, therefore, that:

3 Size Categories of Artillery = 1 Ton of Cargo Space

Rules & Magic says that it takes one barrel of gunpowder per size category to shoot an artillery piece. This is a huge amount of gunpowder! In reality, the amount of powder used per shot depended on the weight of the shot, and the Sealed Knot has this at about 2/3rds the weight of the shot consumed in powder (other reading suggests that earlier on, a 1:1 ratio may have been used). A standard barrel of gunpowder (which didn’t really exist of course) in LotFP is 4 encumbrance points and gives 2500 measures of powder for musket fire. If I estimate the weight of a barrel of gunpowder by encumbrance points I would get approximately 110lbs, and if I estimate the amount of gunpowder contained by the number of shots, I get approximately 80lbs. These are completely uneducated estimates on my part as I have no direct experience with gunpowder, but broadly seems OK to me, although the barrels must be heavy. So, in terms of how much gunpowder a ship can carry:

20 barrels of gunpowder = 1 Ton of Cargo Space

And using the 3:2 ratio which is generally used:

1.5 Tons of Shot require 1 Ton of Powder

Armed with these three facts, players can estimate how many guns, powder, and shot their ship can carry. But what damage can they actually do? And for that matter, what ranges can the different cannon be used at? For this, I am modifying the final table given in this wonderful thread by the poster “Cutter” and adding how many “cannonballs” of ammunition for each of the cannons listed can fit into 1 ton of ship cargo space:

SizeTypeDMG (SHP)Short (‘)Med (‘)Long (‘)Shot per TonShots/barrel

Finally, the artillery rules do not provide prices for shot – just the artillery piece itself and gunpowder (by the barrel). So, extrapolating based on the price of a bag of shot (interchangeable for all firearms in LotFP) and how many musket balls there are in a ton, an estimate price for a ton of shot is:

1 Ton of Shot = 650sp

(This means that, by weight, shot is nearly as expensive as cannon themselves – this might need to be revisited since it seems counterintuitive)

So, we can resolve the question of how many guns and how much ammunition a ship can carry based on the cargo capacity in Rules & Magic. How many could the ship mount for use in combat? I think there are two options here – one is simply to research historical examples of armaments for the specific ship type being used, and the other, to embrace the over-optimistic spirit of the age with respect to quantity of armaments and sea worthiness. Following the logic of the latter, the ship can mount for combat all the guns it can carry (after all, wooden ships can be reconfigured with a little carpentry), once ammunition, gunpowder, rations, water and other vital supplies are also accounted for from the maximum cargo capacity. If you want to put to see in a ship bristling with guns and filled with gunpowder and shot, but with no food and water, so be it. That sort of decision has its own consequences, of course.


Ships can carry and use as many guns as they can carry, provided they also have powder and shot, based on their cargo capacity:

  • 3 Size Categories worth of artillery = 1 Ton of cargo space
  • 20 barrels of gunpowder = 1 Ton of cargo space
  • 20 barrels of gunpowder fires 1.5 Tons of shot; or
  • 1 Ton of shot requires 13 1/3 barrels of gunpowder
  • 1 Ton of shot = 650sp
  • All other prices as per Rules & Magic
  • Gun ranges (and shots per barrel and per ton) as per the table above

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