In the ocean where there are already "seas" and you find wind waves to add to the seas, a 20' beachcat has a lot of trouble getting past any SUSTAINED speeds of 18 knots.

I have had bursts to 22 knots. I have had short moments of sustaining 18-19 knots. (no spinnaker in either case)

I am always happy if I can maintain an average upwind plus downwind speed of 10+ knots. As a cruiser, I am pretty pleased if my speed is above 8 knots in any direction.

My Mystere 6.0 (Whisk) will probably never go faster than 24 knots unless she is riding on a body of water that is not being affected by the wind, the same wind that is pulling her along at such high speeds. (ditch run?)

Whisk won't go faster than 24 knots in the six years that I've sailed her on the ocean. Gross weight = (minimum) 615 pounds to (approx. maximum) 1175 pounds.

GARY