Shape

[DaveOnCudjoe]

The planing vs displacement topic is regularly discussed on the F-boat forum. My F-31 begins to plane at just above 8knts with the main hull and windward float carried unusually high and a slight squat aft. By 9knts everything becomes level with neutral helm and no more change in trim. Speed continues to rise at 100-110% of true wind speed until I chicken out at about 20 or so knts. The boat never pounds and goes over or through waves depending on period and captains mood. I love a sailboat that planes, at 15knts it's smooth,mostly dry and fairly relaxed. Above 15knts you have to be paying attention and wearing foulies. The chines on these boats are rounded but the bottom nearly flat from the daggerboard aft with very slight rocker. It should also be noted that at some point the entire boat is supported by the lee float and the main hull begins to lift. That is why these boats absolutely can not be overloaded because if the float can't support the total weight the entire stability geometry changes to a boat rotating along the axis of the main hull not the float and that is bad. Modern tri's are exhilarating to sail and tremendously forgiving but must not exceed the designers maximum weight. Max weight of an F-31 is 5450 lbs, dry sailaway is about 4000 lbs so you have only 1450 lbs or so for crew and provisions. That is the trade off and the Achillies Heel and the reason so few cruise on tris and so many on cats. Dave