This is an area of interest to me, but finding actual speeds is like digging a ditch with a teaspoon. You find a bit here, a bit there, and once in a great while, how many days it took to press on from one port to another. Due to the recreated ships, you can find out more hard data about Classical galleys in the Mediterranean and Norse ships crossing the Atlantic than about medieval ones.

In general, figure a Venetian galley, under sail with a quartering wind, does 12 kn. They did usually sail, and only took down the mast and rowed when battle offered, or when it was dead calm, or they had a contrary wind.

Rodgers says of Mediterranean galleys "In the thirteenth century the ordinary galleys were about 128 feet long and 17 feet wide with a deep draft of 4.0 to 4.5 feet when they displaced about 130-145 tons. ... Each carried one mast which was usually struck when clearing for action." This would have about 120 rowers, free men who fought for the ship. Sizes ranged down to the "vachette" (little cow) with 8 oars (16-32 rowers), about 23 feet long and 6 feet wide.

Besides the rowers were a captain, steersmen, officers, and an unspecified number of marines, especially crossbowmen.

In a 1313 Genoese law, merchant galleys of large size had to be manned with "12 crossbowmen, 4 pilots, and 162 rowers and seamen, all armed with helmets, cuirasses, darts, swords, maces, and other weapons."

In 1203, Rodgers notes, it took a Venetian fleet under sail 31 days to sail 700 miles, though that includes 8 days at Abydos to wait for stragglers. So let's say 700 miles in 23 days. This is over open sea, not stopping each night along a coast, so it's 24 hr/day, meaning they covered 30-31 miles per day, which is kind of pitiful.

In 1284, the Genoese fleet sailed in pursuit of the Pisans, from Genoa to Porto Pisano in 5 days.

Sources: Naval Warfare Under Oars, 4th to 16th Century by Rodgers. He admits he uses some galleasses in the Spanish Armada as an excuse to be able to include the Armada Fight.

Gardiner, Robert (Editor) The Earliest Ships: The Evolution of Boats into Ships

Parker, Foxhall A., Commodore USN, The Fleets of the World: The Galley Period

This makes me want ebooks of Rodgers, so I can Search rather than eye-scan around the Crusader battles.