The top speed when using oars for propulsion doesn’t matter much for travel because crews can’t sustain it for long, despite one trip being done at 8 knots (which we can have our swaggering hero achieve because he’s awesome). Ships would travel under sail for a trip of any length, with the oars being saved for a battle or a crisis. With favorable winds, a ship can do 2-3 knots while an unfavorable wind is half that (1-1.5 knots). For more details on calculating travel times, consult the next section.
Surface currents on rivers are arguably stronger than those on larger bodies of water due to the narrowness of the channel. The narrower the river, the faster the current, but depth can also make it faster. A river is not uniformly wide or deep and will become wider, and therefore slower, the longer it flows. This means river speeds farther inland are faster. A river’s course also affects speed. Water flows faster in the center of a straight channel, but when it curves, the outer corner is fastest and the inner one slowest. Characters who are inexperienced sailors might be unable to utilize the currents well unless they happen to be keen observers and figure this out. How fast do rivers typically flow in knots? The extremes are almost 0 knots to 6 knots, but we’ll typically want to aim for 1-4 knots for travel. Faster than 4 knots on a river might mean it is treacherous.