Propulsion
Throughout their long history, galleys relied on rowing as the most important means of propulsion. The arrangement of rowers during the 1st millennium BC developed gradually from a single row up to three rows arranged in a complex, staggered seating arrangement. Anything above three levels, however, proved to be physically impracticable. Initially, there was only one rower per oar, but the number steadily increased, with a number of different combinations of rowers per oar and rows of oars. The ancient terms for galleys was based on the numbers of rows or rowers plying the oars, not the number of rows of oars. Today it is best known by a modernized Latin terminology based on numerals with the ending "-reme" from rēmus, "oar". A trireme was a ship with three rows of oarsmen, a quadrireme five, a hexareme six, and so forth. There were warships that ran up to ten or even eleven rows, but anything above six was rare. A huge forty-rowed ship was built during the reign of Ptolemy IV in Egypt. Little is known about its design, but it is assumed to have been an impractical prestige vessel.
Ancient rowing was done in a fixed seated position, the most effective rowing position, with rowers facing the stern. A sliding stroke, which provided the strength from both legs as well as the arms, was suggested by earlier historians, but no conclusive evidence has supported it. Practical experiments with the full-scale reconstruction Olympias has shown that there was insufficient space, while moving or rolling seats would have been highly impractical to construct with ancient methods. Rowers in ancient war galleys sat below the upper deck with little view of their surroundings. The rowing was therefore managed by supervisors, and coordinated with pipes or rhythmic chanting. Galleys were highly maneuverable, able to turn on their axis or even to row backwards, though it required a skilled and experienced crew. In galleys with an arrangement of three men per oar, all would be seated, but the rower furthest inboard would perform a stand-and-sit stroke, getting up on his feet to push the oar forwards and then sitting down again to pull it back.
The faster a vessel travels, the more energy it uses. Reaching high speed requires energy which a human-powered vessel is incapable of producing. Oar system generate very low amounts of energy for propulsion (only about 70 W per rower) and the upper limit for rowing in a fixed position is around 10 knots. Ancient war galleys of the kind used in Classical Greece are by modern historians considered to be the most energy efficient and fastest of galley designs throughout history. A full-scale replica of a 5th century BC trireme, the Olympias was built 1985-87 and was put to a series trials to test its performance. It proved that a cruising speed of 7-8 knots could be maintained for an entire day. Sprinting speeds of up to 10 knots were possible, but only for a few minutes and would tire the crew quickly. Ancient galleys were built very light and the original triremes are assumed to never have been surpassed in speed. Medieval galleys are believed to have been considerably slower, especially since they were not built with ramming tactics in mind. A cruising speed of no more than 2-3 knots has been estimated. A sprint speed of up to 7 knots was possible for 20–30 minutes, but risked exhausting the rowers completely.
Rowing in headwinds or even moderately rough weather was difficult as well as exhausting. In high seas, ancient galleys would set sail to run before the wind. They were highly susceptible to high waves, and could become unmanageable if the rowing frame (apostis) came awash. Ancient and medieval galleys are assumed to sailed only with the wind more or less astern with a top speed of 8-9 knots in fair conditions. In ancient galleys, most of the moving power came from a singe square sail on a mast rigged a little forwards of the center of the ship with a smaller mast carrying a head sail in the bow. Triangular lateen sails are attested as early as the 2nd century AD, and gradually became the sail of choice for galleys. By the 9th century lateens firmly established as part of the standard galley rig. It was more complicated and required a larger crew to handle than a square sail rig, but this was not a problem in the heavily-manned galleys. Unlike a square sail rig, the spar of a lateen sail does not pivot around the mast. To change tacks, the entire spar, often much longer than the mast itself, had to be lifted over the mast and to the other side, a complex and time-consuming maneuver.
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