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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Actually, I'm pretty sure that due to wavemaking and the way oars (and propellers, for that matter) work, it's more like a cube root, so half power gets you most of the speed.
Though, when I was trying to work out real life battleship ranges to get fuel consumptions, and wanted an estimate of their ranges all at the same speed, I found that the numbers came out all over the place, but seemed to average about a 2.5 power.
One of the problems is that engines (and oarsmen) have an optimal output and lose efficiency outside that, in some cases enormously. Another is that ships have several sources of drag, and they scale differently with speed, and some matter more at low speeds, others at high speeds. To make matters worse, just how they scale and which one matters more depends on the size and shape of the ship, not just the speed.
TL;DR Ship performance is very complicated.