Having grown up on lake erie I have found that when you begin to see the white cap on the wave you are at a 2 foot wave, as the white cap gets bigger so does the wave obviously. If I see a good 4-6" of white cap then I know it is a good 3 ft wave etc. Now the real problem I see is the lousy weather forecasting that is going on these past few years. Yes it is getting less accurate each month. I use three different wind and wave forecasts and then take an average or the best two of the three but on some days all three are dead wrong. Just last Monday all 3 stations forecasted 1 ft waves but when we got out there it was 3 ft plus. Now they died down to 1 ft in the afternoon but the morning was quite rough. As far as boat size/wave size I have a 22' and I draw the line at 3ft. if 3's or less then go but if 3's or more I make it another day. The boat can handle the waves, it just isn't fun being tossed around in the boat, have come home bruised before just because it was so rough.