Many of the lakes ships were built with a separate row of sweep ports.

The twin US brigs Niagara and Lawrence, on Lake Erie, had 18 sweeps each, and each sweep was 25 feet long, according to Walter P. Rybka (the captain of the modern day Niagara replica).

The sweeps helped with getting under way and maneuvering in narrow channels.

Rybka mentions the occasional opportunistic role of sweeps in battle this passage from his book, The Lake Erie Campaign of 1813 (p. 85):

"The immediate risk that Perry took by this change in course [sailing bows toward the enemy] was in exposing his vessels to raking fire while closing the range...there lurked the even greater risk that the breeze would die out altogether and leave the Lawrence dead in the water before achieving carronade range...The one hope then would have been to use the sweeps to close the range.Speed under sweeps was at best 2 knots..."

There's a picture on p. 89 of the book, showing a sweep demonstration aboard the modern-day Niagara. It shows three crew per sweep, so I guess you'd need 54 men in good shape to work them if all were in action. His caption says these demonstrations have shown that "even untrained rowers can move [the Niagara] along at 1.5 to 2 knots."