Paired boat engines should have one of them rotating the opposite direction. Assuming you did so, curious to see if they both make the same power in opposite directions.....
Not on stern drive applications. The outdrive takes care of the prop direction. On the Volvo drives you actually flip the shift lever so one is in forward and one is in reverse when each shifter is pushed forward into "drive". On inboard and V drive boats they used to run reverse rotation motors but they don't do that much anymore.