what were the RPM's, and how deep was the cavitation plate? Pontoons are primarily a displacement hull (unless you have plenty of power and lifting strakes).
rough general rule the maximum speed of any displacement hull--commonly called its hull speed-is governed by a simple formula: hull speed in knots equals 1.34 times the square root of the waterline length in feet (HS = 1.34 x √LWL)
for your 22' pontoon, 6.3 knots (about 7.2mph)
