Is 21HP on the Ericson 35 ok?
Seems like you''ve answered your own question by saying that most of them seem to have that engine. If this is a 35-3, with two earlier versions, Ericson should have been able to figure out if more power was needed, and most of them would have that. If you find the chop overpowering, getting a new prop could be an alternative a lot cheaper than a new engine. Dave Gerr talks about this some in one of his books. One reason for heftier horsepower in the current crop of designs is the need to deliver race boats to the the start at 10-12 knots, because you can''t get the fifteen guys needed to sail the thing until its actually race time.