Interesting! The rowing profession was very respectable indeed, and in this era the use of slaves was very unusual, if not nonexistent. What we see in the Ben-Hur movies is possibly an anachronism taken from the Spanish galleys of the Middle Ages, where the oarsmen were indeed slaves or convicts. The only exception to this that I know was the Arginusae battle, where a conscript fleet with slaves and non athenian citizens was assembled to relief the trapped main fleet.
about triremes' fragility:
To strengthen and protect a hull made in this way from rough seas, the Greeks used devices called 'under-belts' (hypozomatd). These were probably heavy ropes fitted low down in the ship and stretched by means of windlasses from stem to stern. In the Naval Inventories four are the norm for each ship, while six are taken on distant missions. Indeed when a trireme was in commission she was often described as 'girded', that is, with the hypozomata fitted. An earlier Athenian inscription, dating to around 440 BC, gives a decree prescribing the minimum number of men (probably 50) allowed to rig a hypozoma. It is clear that considerable tension was required. Apollonios of Rhodes, describing the building of the Argo, says that the Argonauts 'first girded the ship mightily with a well twisted rope from within, putting a tension on each end so that the planks should fit well with the tenons and should withstand the opposing forces of the sea surge'.
Creator of Qvadriga and Mare Nostrvm