Sailing will be interesting, since there are multiple factors (some of which are “known unknowns” at this point). Obviously, wind direction and wind speed matter. So, also, does the type of rig (square sails, fore-and-aft, etc). That rig can have effects on the crew size (lateen rigs in particular require more crew for a given sail size).

WARNING: HIGHLY TECHNICAL (and potentially boring to laymen) DISCUSSION BELOW

One thing I am trying to do right now is work on some mathematical formulas to help me work out ships I’m not terribly familiar with. Part of this has involved learning about block coefficients and hull speeds.

Block coefficient is a way of describing (in a number) the overall shape of the hull underwater. To illustrate, if you multiply the length, beam, and draft of a hull, you get a number that assumes the shape is a perfect cube. However, ship’s hulls are streamlined to some extent, even on barges. The ratio of the actual volume of the hull underwater to the perfect cube is the block coefficient. Most ships are between a .4 (for a sleek yacht) and .8 (for a ultra large crude carrier - the giant oil tankers). This, in turn, ties into the tonnage of the ship, since the volume of water actually displaced has a mass equal to the tonnage of the ship. Being able to estimate block coefficient based on known dimensions lets me estimate tonnage for ships that don’t have a listed tonnage (or, on the flip side, if I have length, beam, and tonnage, I can estimate draft). The polyremes already done have block coefficients ranging from .35 (for the bireme) to .54 (for the quinquereme), averaging .47. This suggests they’re adequately streamlined, and that the bireme and trireme may be a bit light (they’re at .35 and .36, every other polyreme is at .47 or higher). Then again, they are the light warships.

Hull speed is the theoretical maximum speed of a hull, which is directly related to length - it’s 1.37 times the square root of the length of the hull (in feet). Many modern ships can go faster than this through planing or shaping the hull to change how waves form off the bow and stern, but for ancient ships, it’s an adequate rule of thumb for determining maximum speed. In my case, I’m also using a factor based on the block coefficient to figure hull shape into speed - that sleek racing yacht will, for the same length of hull, be faster than the blocky tanker (or, in ancient terms, the galley will perform better than the cog). Based on this, the maximum theoretical speed for the polyremes ranges from 13 knots to 15 knots, so I’m pretty happy with the burst rowing speeds of 9 to 11 knots, since those are under the maximum speeds and the power produced by the rowers may not be enough to get to maximum speed.