I also fish an 18 footer. I try to stay away from anything gusting to 20 mph or more. Also, anything out of the north is usually not good. I will fish in 2-3 footers but I usually take a beating and it seldem pays off. I don't trust the marine forecast much at all. I highly recommend the app iWindsurf for wind forecasting. Another good one is Windfinder. The winds and waves change significantly and quickly out there!