Quote:
Originally Posted by Rupert
... or make some more detailed rules that allow for 'hiking', 'running', and 'sprinting' speeds.
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Quote:
Originally Posted by johndallman
At constant speed, thrust from rowers is equal to drag. And drag is proportional to velocity squared. So if you halve the number of rowers, you divide speed by sqrt(2).
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I previously worked out an alternative system for towing, poling, and rowing vessels,
here. The tl;dr of the final system is:
Step 1) Divide the weight of the vessel by its length in yards. That value works as-is for rafts and square barges; for a vessel with rounded lines, multiply by 0.7; for a vessel with long lines, multiply by 0.5. This is "effective weight" (
eW).
Step 2) (
poling/rowing only) Combine the BL's of all polers/rowers. For poling (and paddling, basically any "arm only" option), use 30xBL for sustained poling (functioning similarly to Hiking), 70xBL for more rapid poling (comparable to Jogging), and 150xBL for full-speed (comparable to Sprinting). For rowing, these values are instead 50xBL, 100xBL, and 200xBL, respectively. The end result is "power" (
P).
Step 3) For towing, use eW multiplied by Move squared as encumbrance (spread out over all characters/creatures involved). For poling/rowing, divide P by eW, then take the cube root of the result to determine maximum Move. That is:
Towing: eW * Move^2 = encumbrance
Poling/Rowing: (P/eW)^(1/3) = Move
In all cases, Move is relative to the flow rate of the body of water. If you need to tow a vessel on a river, subtract the flow rate from Move before squaring it if traveling downstream, add the flow rate to Move before squaring it if traveling upstream. If you need to pole/row a vessel on a river, add the flow rate to the determined maximum Move if traveling downstream, subtract it if traveling upstream.
As an example, let's take a 10-yard raft, and load it up to 1000 lb (including its own weight; note I'm just pulling numbers out of the air, here). It has an eW of 100 lb (1000/10). Towing it at relative Move 1 reduces the half-ton load to 100 lb - with 5 people of average ST, they'd each be right at Light Encumbrance (20 lb), and could comfortably move at Hiking speed. Towing it at a relative Move 2 means that half-ton load is instead 400 lb (multiply by 2^2), meaning either Extra-Heavy Encumbrance (and the characters cannot get up to Move 2 anyway; they might be at this level if towing upstream, however) or needing more people (or stronger animals) doing the towing. (EDIT: Also, note that in this case, if you need to move much faster than 3 yards/second relative to flow rate, you're better off just carrying it - the break-even point is the square root of 10, or around 3.16) Five people poling or rowing it means a combined BL of 100. Poling at a "hiking" rate means a P of 3000 (30x100), a P/eW of 30, and thus a maximum Move of 3.1 (cube root of 30). Poling at a "jogging" rate means a P of 7000, a P/eW of 70, and maximum Move of 4.1. Poling at a "sprinting" rate gives a P of 15000, a P/eW of 150, and a maximum Move of 5.3. For rowing, the maximum Moves are 3.7, 4.6, and 5.8, respectively.