How did the ancient triremes work?

Having a drummer would help. I also think that after rowing each person would take their oar outside of the water. If they kept it in the water, it would interfere with the rowers on the other levels.

https://discover.hubpages.com/education/trireme

Scroll don to the cross-section ! Each level had a different length oar.

I don’t see any mention of oar length.

I am mistaken about the different levels moving at different times. I found this, which talks about the construction of a replica of a trireme. At about 4 minutes, you can see all the oars moving at once. Rather impressive looking.

Seeing a picture or drawing of one, it isn’t hard to tell that the higher up the oars extend from, the longer they are. Proper training of the crews keep them in order and in time and away from the other oars.

We have a competitive rower on Fluther. I hope they chime in.

The three rows of oars were staggered, the lowest row of men were closest to the outside of the hull with oars that were maybe (as an example) 9 feet long. The next higher up row of men sat closer to the center of the ship because they needed more leverage to operate their (maybe 8 foot) longer oars, and these oars struck the water beyond the reach of the oars of the lower row. The next row of men rowed from a position beside the center of the ship, for the leverage to operate their oars that might have been (for example) 16 feet longer that the oars of the bottom row.
Properly timed rowers could operate together with all oars being in the water at the same time with each row of oars being either beyond the reach or within the reach of the oars from top row to bottom row, side by side in the water in unison.
It’s possible that a copy of the movie BEN HUR or CLEOPATRA would show these ships in action.