There is evidence from the Renaissance that oarsmen on galleys developed in a lopsided manner if they only pulled on one side.
If they were only on the left bank of oats, then the muscles on your left side became bigger and stronger.
If you only pulled on the starboard oarsmen, your right side became bigger and stronger.
The Venetian s recognized this and trained their oarmen to work on both sets of oarsmen.
Also, contrary to Hollywood, they did not use slaves.
"These things must be done delicately-- or you hurt the spell." - The Wicked Witch of the West.
"We've got the torpedo damage temporarily shored up, the fires out and soon will have the ship back on an even keel. But I would suggest, sir, that if you have to take any more torpedoes, you take 'em on the starboard side." Pops Healy, DCA USS Lexington.