Minimum planing speed

[<KC>]

What is the minimum speed at which a board can plane? In really light wind some people can seem to plane earlier, so what is the limiting thing these guys over come first. I guess I'm asking what stops a board from planing and how to overcome that.

[sukhdev]

Good question, if I recollect correctly its in the 12 to 15knot range, ie when you are just planing this is the speed you are doing, but I'll check other sources to see if its true.

Your second question is tougher. When not planing, any water craft has drag which increases with the square of its speed. Basically as you start going faster thru the water, but not yet planing, your "push" is resisted by creating waves. You will then come to a point where the length of the wave generated by your forward motion will be the same as the length of the craft.

This is a sort of brick wall as now to go any faster the craft has to climb over the wave generated by its own motion. Since the wave is generated is dependent on the length to width ratio of the craft, this happens later in long narrow craft and happens earlier in short wide craft. Therefore either you make a long narrow craft to delay this hump (eg displacement sailing yachts) or you escape the hump by planing.

To plane you need to generate enough power to climb over this hump. This can be done either by having lots of power (bigger sail/fin) or by cheating (pumping, going down a wave). Whichever method is used, once you are planing you are free from the wave making rule and you are running on apparent wind.

So to sumarise that complicated explanation, good sailors overcome the early planing hump by active pumping of the hull as well as using the water surface (chop etc).

Next part of your question,what stops the hull from planing...once planing when you hit a lull, the power from the sail/fin combo may not be enough to continue lifting the weight of you, the board and the rig out of the water. At this point you will drop back to displacement mode. A good sailor will unhook just as the lull hits and start pumping especially if the lull is a small one, this may be enough to keep on the plane till you get into the next gust.

sorry about all the diluted physics but its really worth understanding this stuff, makes it alot easier to relate to what  you need to do to plane early and to keep planing.