About 19-1/2' to 20' with the mast up. Just under 17' with the mast down and bimini up on mine. Allegedly 14' to the top of the flybridge wind screen, but I haven't tested that.
You buying one? Bought one? FYI, The Prairie was marketed as a "36' Coastal Cruiser." Atlantic sold the same hull as a 37. To my knowledge, there is no "Prairie 37."