Modifying Ships

After doing some light research, I’ve discovered that it is quite possible that the cargo loads of ships in ACKS are overstated by about an order of magnitude. If I were to reduce the cargo capacity of ships to a tenth of the listed values, what would the follow-on effects in the game be? For instance, how would it affect the profitability of ships, and would that alter other values?

Hi faoladh! What leads you to conclude the cargo loads are overstated? 

If you look at B/X D&D, the cargo loads are 1/10th of what they are in ACKS. I increased them because my research showed that B/X D&D had understated the cargo loads by an order of magnitude. It's possible I made a whopper of an error so please fill me in.

To answer your specific question, it makes a huge difference. It would affect the profitability of ships, meaning the rate of return from mercantile activities. That would in turn suggest the rate of return on other actitivies might need to be different. It all cascades...


As Beedo (of Dreams In The Lich House) was looking into the matter, a significant and important difference between dead weight and displacement tonnage became apparent. Displacement tonnage is largely a matter of volume, having to do with flotation, and is the usual measure for describing ships, while dead weight tonnage is what we normally think of as “tonnage”, being the actual weight of cargo (and what you seem to be using as cargo capacity, based on the use of stone weight). Examination of the hauls of pirates and privateers seemed to indicate that cargo capacities were in the lower range, closer to B/X, rather than the higher ones you chose to use. I mentioned ACKS, and he reiterated the lower values. I said I’d write and ask, and here I am!

I figured that there would be a lot of follow-on effects, which is why I am asking. :wink:

Beedo's analysis is interesting, but it doesn't mean the data in ACKS is wrong.

Here is an example of the historical evidence of what the ships could actually carry:

"The capacity of ancient merchantmen may be judged from indications of their cargo or their dimensions. The stone for some archaic masonry was carried by sea; there are surviving statues of more than 20 tons and blocks of more than 30. Round ships could carry considerably more. Gifts of grain to Athens in the late 4th century BC are attested in quantities of 300 medinnoi (120 tons) and less frequently of 4000 medimnoi (160 tons) and they are plausibly whole shiploads. The 3000 wine jars that were the cargo intended in Demosthenes 35 are likely to have exceeded 100 tons. A decree from Thasos of the 3rd century BC excludes ships carrying less than 300 talents (80 tons) from one harbor and ships carrying less than 5000 talents (130 tons) from another. There is evidence of much larger cargoes. Prvileges in the Roman period were available in respect of vessels carrying at least 50,000 modii (340 tons) of grain and there are wrecks of the Roman period with more than 400 tons aboard. The vessel that bought the Vatican obelisk to Rome must have been able to carry around 1300 tons (see Pliny, Naturalis Historia, 16. 201); vessels with such dimensions seem from the tone of Pliny's reference to have been unusual enough to provoke wonder. The largest vessel that is known from antiquity was built in the 3rd century BC for Hiero of Syracus; its size has been estimated at around 2000 tons. It is not until the 19th century that ships became substantially larger." p.654, Ships and Shiping, "Ancient Greece" by Nigel Guy Wilson

In light of the above, consider that in ACKS, a large sailing ship can carry 150 tons and a small sailing ship can carry 50 tons. That does not even push close to the upper limit of what actual ships in antiquity could carry. B/X D&D, putting them at 15 tons and 5 tons, was absurd when actual Roman ships have been found carrying 400 tons of cargo.


OK, but the original question still stands. What values in the game would be affected by reducing ship carrying capacities, and in what ways, should one choose to do so? This could also apply to people who intend to include larger ships with 300-400 ton carrying capacities.

Maybe that’s too big a question for forums, but it’s the one I have right now.

On an upfront cost versus net profit basis, sea trade is currently competitive with land trade, and has better range. That makes sea trade more attractive than land trade by an adequate margin, even between nearby cities. Building a coastal or riverine city makes sense!

If capacity is reduced, the upfront cost balloons (see below), and sea trade becomes non-competitive with land trade at short ranges . . . and at long ranges, the reduced capacity means you can’t keep the crew fed.

Coastal cities start to make less sense than land-locked cities close to each other and natural resources. Riverine trade becomes less useful than overland travel.

Take a small sailing ship.

Capacity is 10,000 stone (crew is an invisible 1,800 stone). Six months of food and water uses up 2,000 stone, leaving 8,000 stone for cargo.

Halve the capacity to 5,000 stone (crew is still an invisible 1,800 stone). Six months of food and water uses up 2,000 stone, leaving, er, 3,000 stone for cargo. Halving the capacity almost triples the upfront and monthly cost per ton of cargo. Worse, traveling any length of time at all eats into your cargo so much, you’ll have difficulty paying the marines out of the profit - short range trade is the only viable option, and for that, land travel is less expensive.

Reduce the capacity by an order of magnitude to 1,000 stone and you can’t travel more than a month or two and still have any cargo at all.

On the other hand, ships the size of a small sailing ship in ACKS aren’t, as far as I know, making multi-month voyages without re-supplying, especially for water and “green stuff”. When I run saltbox games, I assume no more than a few weeks at sea without having to resupply (by mundane or magical means). If nothing else, it lines up with the period of iron rations’ edibility.

I think you have to be careful about gauging things from, eg, the haul from the Cacafuego, because the value of the cargo is another limiting factor is what was on that ship. That is, it’s not just the weight of gold that mattered, but how much gold from the Spanish treasury was available to be transported. There’s also a concern of density of cargo (is a bunch of gold so heavy in so small an area that it stresses the beams of the ship). But assuming the uniform distribution of weight (which may not be optimal for sailing), the displacement tonnage and the dead weight tonnage are inextricably linked: Whatever the difference between your unladen and safely laden water lines is marks the volume of water’s weight you can carry, right?

Just to reply to myself, Beedo references cogs, and cogs are really tiny little merchant vessels that sail near the coast.

Thanks for taking up the question, fellas. I’m focused on a later period, but I’ll put the question another way - the builders old measurement for calculating tonnage is [length in feet x breadth x height of hold / 100] to get ship capacity in tons, the traditional figure used to calculate volume capacity for charging harbor fees. Using the measurements of a galleon, let’s accept the capacity comes out to be 400 tons.

The first issue I have is recognizing that a ship like that might have 50+ cannon, ranging from a 1/2 ton to a ton in weight each, plus ordnance. A galleon could have a crew and marines in the 200-250 person range, plus the necessity of accounting for provisions and water for a long journey. A first problem is identifying a reasonable cargo capacity after assuming that full load of armaments, crew, and ordinance - or doing the tedious thing and calculating out load… for everything.

It is a question that could apply to ACKS shipping - as Thomas points out - though not as extreme, without all those bronze and iron cannons and gunnery crews. The ACKS-oriented question might be how much to reduce cargo capacity for crew and their provisions.

You would think it wouldn’t be that hard to find sources from the 16th-17th centuries that discussed actual galleons, loaded with crew, cannons, provisions, etc, and managed to relate what kind of trade cargoes they could still carry over and above. I’m sure they’re out there, just not in the books I’ve had access to thus far. Still looking.

I also find myself questioning the measures because of the ambiguity between ton as a unit of weight, and ton as a historic volumetric measure (where a ton was used to mean a 250 gallon barrel or so). Tons of grain (volume) seems a much different animal than tons (weight) of precious metal. However, those anecdotes about the Roman stone hauling are super interesting. I’d like to see how they loaded a 30 ton rock on a ship.

I had another thought on the ship size question on the way to work… If a hypothetical sailing ship can carry 150 tons of treasure, how big is the actual ship in terms of displacement tonnage?

The simple (non specific) answer - it’s as big as it needs to be… Not wholly satisfying, but I’m not sure a relationship between actual dead weight tonnage and volume capacity can actually be determined, unless maybe some of the folks building replica wooden sailing ships have made some empirical observations.

This is a very interesting observation, actually. One of the characteristics of sea voyages in late antiquity and the pre-Renaissance in general is that they did not last for very long. This is a likely reason that the New World was not “discovered” until a much later date (except, of course, in voyages in the North Atlantic, which allow for a series of much shorter voyages to get there). So, what is needed is an examination of sea travel and trade in other areas than Europe in order to develop a clearer model of what was going on. My suspicion at the moment is that the much larger designs of Chinese vessels (for instance) allow for longer journeys, even with larger crews, due to the greater cargo capacities possible.

So, that’s one way to ensure that the PCs won’t be making around-the-world journeys.

This post makes use of some material in's_Old_Measurement.

To determine the displacement of a ship, we multiply its length by its breadth and the draft, all in feet. Then we multiply the product thereby obtained by the block coefficient of the hull (which averages 0.62). This yieldst the hull volume in cubic feet. We then multiply this figure by 64 (the weight of one cubic foot of seawater) to get the weight of the ship in pounds, which is e.g. the weight of water it is displacing.

In ACKs, a Large Sailing Ship has a 100’ to 150’ length, 25’ to 30’ beam, and 10’ to 12’ draft.

A Large Sailing Ship with 100’ length, 25’ beam, and 10’ draft therefore has a displacement tonnage (weight) of (100 x 25 x 10 x 0.62 x 64) 992000 lbs, or 496 short tons.

A Large Sailing Ship with 150’ length, 30’ beam, and 12’ draft has a displacement tonnage (weight) of (150 x 30 x 12 x 0.62 x 64) 2,142,720 lbs, or 1,071 short tons.

London shipbuilders assumed that a ship’s burden (tonnage of cargo) would be 3/5 of its displacement. Therefore the Large Sailing Ship’s tonnage of cargo would be 297 tons to 643 tons.

From this we can conclude that ACKS has likely underestimated the cargo carrying capacity of Large Sailing Ships.

And we can calculate backwards to answer Beedo’s question: “If a hypothetical sailing ship can carry 150 tons of treasure, how big is the actual ship in terms of displacement tonnage?”

150 tons of treasure = 300,000 pounds
Ship’s Burden = 3/5 x Ship’s Displacement
300,000 = 3/5 x Ship’s Displacement
5/3 x 300,000 = Ship’s Displacement
500,000 = Ship’s Displacement
500,000 = 250 tons

That’s really great Alex, thanks. I hadn’t seen that assumption of 3/5ths displacement as a factor for calculating burden, that was a missing link.

I found some books that should provide insight on variances by hull types, more detail than is necessary here, but as they’re out of print ($$$) I’ll have to wait until after the holidays. This is enough for most purposes.

Cool! Let us know what you discover. I did not extensively research ships for ACKS, just enough to notice that B/X was off!