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Paizo has no clue about ship propulsion systems.
Also, there is a difference between tactical movement (where galleys outpace sailing ships ridiculously, plus they can move in any direction they want regardless of the wind) and large-scale movement (where a sailing ship going with the trade winds can sail at 6-8 knots for at least 6-8 months, whereas the galley crew's arms fall off from exhaustion at 6-8 hours, and they all die of thirst in 6-8 days if they don't beach and drink some water)
Overland movement rates assume people travelling by foot for 8 hours (maybe 12) and sleeping for 8 hours. Sailing ships can go round-the-clock because their motive force doesn't suffer fatigue.
And this is even before we get into the difference that winds and currents can make.
But unless your players are Age of Sail aficianados, I recommend just assuming that the Paizo speeds are "average". Add/subtract a random factor based on the weather (and realize that unless the players can control the weather, sailing often involves really amazing amounts of maniacal patience as the winds do whatever they want, particularly if you're close to shore instead of in the open ocean.)
Recommending reading: the opening chapters of Samuel Eliot Morison's The European Discovery of America.