Armament and Tactics
A change in the technology of conflict had taken place to allow these juggernauts of the seas to be created, as the development of catapults had neutralised the power of the ram, and speed and manoeuvrability were no longer as important as they had been. It was easy to mount catapults on galleys; Alexander the Great had used them to considerable effect when he besieged Tyre from the sea in 332 BC. The catapults did not aim to sink the enemy galleys, but rather to injure or kill the rowers (as a significant number of rowers out of place on either side would ruin the performance of the entire ship and prevent its ram from being effective). Now combat at sea returned to the boarding and fighting that it had been before the development of the ram, and larger galleys could carry more soldiers.
Some of the later galleys were monstrous in size, with oars as long as 17 metres each pulled by as many as eight banks of rowers. With so many rowers, if one of them was killed by a catapult shot, the rest could continue and not interrupt the stroke. The innermost oarsman on such a galley had to step forward and back a few paces with each stroke.
Read more about this topic: Hellenistic-era Warships