I have a 51'' offshore (low freeboard and interior volume) aft cockpit boat. It is cooled by two units. 16,000 btu''s handles the forward 2/3rds of the boat and 9,000 btu''s handles the aft third. On a hot sunny day, the units will often run almost continuously to drop the inside temp 10 degrees. Given the fact that my boat is a "small" fifty footer, it probably doesn''t have much more interior volume than your 42'' center cockpit. 22,000 btu''s sounds like it may be marginal in a warm climate.