OED Wilderness Rules Draft: Carrying Capacity

More suggested refinements to OD&D wilderness adventuring mechanics. Notice how in this installment we use modern research to establish a mathematical formula between real-world creature weight and carrying capacity (in line with our observations last week). So: It's simultaneously more realistic, and also (perhaps more importantly) simpler to judge and to generalize. Comments?

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Carrying Capacity

Animal carrying capacity is shown in the table to the right, as well as average weights for such mounts. All weights are given in stone. Light load (full move) is considered to be up to 20% of the animal’s weight; heavy load (half move) is set at 40% of animal weight.

Vehicle and ship capacity is given in the next table; units here are in tons (160 stone). Note that as a convenient rule-of-thumb, the capacity of the vehicle is its cost (from Vol-1), divided by 100, in tons. Galley types are the exception, with a capacity half normal by this rule (or in other words, about 1 ton per crewman; see Unger p. 176). Do not count normal crew against the cargo capacity given here (although any added soldiers, pilgrims, horses, etc., will be counted). Treat longships as small galleys, and warships as small merchant ships for this purpose.

Of course, in reality both animals and ships vary continuously in their size, weight, strength, carrying capacity, etc. As DM you may wish to permit a range of sizes for each (and load capacity can be fairly easily found by the rules-of-thumb above). This is easier to do with ships (likely only one owned by a given party), and harder to do with beasts (where many may be owned per party). Maximum constructable size for a merchant ship (cog) may be up to around 400 tons capacity in this time period.

For simplicity, assume that an unarmored man weighs about 10 stone, and medium or heavy horse with one week of hay and water weighs 1 ton.

Note and References

• AD&D gives higher load rates than we do here, but also ranks weight of armor and other equipment generally higher than we do. In principle, mules should have higher endurance than horses, but that is not dealt with here (DM’s option).
• Comments on medieval army move rates, with supply carts and weather, here: https://www.quora.com/How-far-could-a-medieval-army-march-in-a-day
• Wikipedia articles on types on mounts (includes size, weight figures; multiple sources say capacity 20% dead weight, 30% live weight): https://en.wikipedia.org/wiki/Mule, https://en.wikipedia.org/wiki/Draft_horse, https://en.wikipedia.org/wiki/Horses_in_warfare
• Japanese researchers find horses lose symmetric gait at about 30% live weight: http://www.thehorse.com/articles/31900/how-much-weight-can-horses-comfortably-carry
• On horse carrying capacity (include saddle & pad, 25 lb.): http://www.equinews.com/article/horses-weight-carrying-ability-studied, http://maverickhorsebackriding.com/2016/03/29/what-is-the-carrying-capacity-of-a-horse/, http://www.horsechannel.com/horse-experts/horse-vet-advice/safe-weight-horse-carry.aspx, http://www.horseclicks.com/horse_advice/how-much-weight-can-a-horse-carry-/283
• Cal State study (20% weight load only slows horse speed from 7.4 to 7.0 mph, i.e., about 5%): http://equusmagazine.com/article/weight_carry_062608
• Camels can go 5 days without water in summer, up to 6-7 months in winter while eating green herbage: https://www.reference.com/pets-animals/long-can-camel-water-b03da9e312a48695, https://en.wikipedia.org/wiki/Camel
• Wagon design and loading (1, 1.5 ton cargo): http://www.humanist.de/rome/rts/wagon.html
• The “ton” considered here is the UK “long ton”: https://en.wikipedia.org/wiki/Ton
• Details on shipping: Unger, Richard W., The Ship in the Medieval Economy 600-1600. (esp. Ch. 3-4, AD 1000-1400).

Update

After great observations in playtests from our patrons, we revisited the issue of horse carrying capacities and became convinced from modern research that 30% body weight -- or say, 1/3 for a simple fraction -- is a better cutoff for the point where horse mobility starts to fall off. (Or in other words: the modern 20% rule-of-thumb is highly conservative, kind to the animal, and has a large safety overhead built-in). This results in our 60-90-120 stone horses having light-load cutoffs at 20-30-40 stone, which seems to work pretty well, and happen to be quite close to the Original D&D numbers. See here for more.