I ran across a discussion thread that is too old to respond to, so, it seems that on that thread, it was observed that the less pounds per square inch of planing area, the more lift (that is planing) you get earlier. That's as far as that thread went, so, does anyone out there know of a theoretical or rule of thumb optimum pounds per square inch vs. getting below that number (too few pounds per square inch) just getting too draggy? This would be viz Formula (a.k.a. really really wide high aspect planing surfaces) boards, for some sort of reference point.
Yes I agree, although it's the opposite end of the spectrum, optimising speed over early planning, instead of optimising early planning instead of speed.
I'm sure somebody there has done the maths, and it should be applicable to both disciplines.
But they will most probably be working in metric, not that ancient clumsy imperial stuff!
So you are seeking a rule of thumb that will enable you to estimate the planing threshold of a hull given the all up weight and sail and fin sizes?
That could be a universal index for all hulls couldn't it sort of like the mast stiffness index. Manufacturers could publish a planing index alongside the volume, width and length of each model.
The variables at play in real world threshold planing speed are all up weight, hull area and aspect ratio, fin size, sail size and wind strength. It seems all too complicated to get a quantitative calculation that returns the actual threshold planing speed of a particular setup, but an index would certainly offer a valid and simple means of comparing that quality in different boards. I suspect it wouldn't be much different from a straight forward comparison of widths though, but I'm just guessing.
http://www.hydrocompinc.com/knowledge/whitepapers/HC113-MinPlaningSpeed.pdf
This paper suggests that a rule of thumb for calculating planing speed (for boats?) is:
velocity in knts = k * LCG / SQRT (B)
k = Constant 4 for feet, 7.2 for metres
LCG = Distance from logitudinal centre of gravity to transom
B = Beam
Not sure how applicable it is to windsurfing, as you can radically change your CofG. The formula indicates that putting all your weight close to your tail would decrease your min planing speed, but practically, we know that mast foot pressure is essential to getting onto the plane early.
It also seems to disregard mass.
Center of gravity will be between the sailor's legs (ahem!) so call it 1 metre from the transom.
Beam is 65 cm, so 0.65m.
V = k * LCG / SQRT (B)
V = 7.2 * 1 / SQRT (0.65)
V = 7.2 / 0.8
V = 8 knots.
What the formula fails to address is hull speed ( en.wikipedia.org/wiki/Hull_speed ), which will make a longer narrower board get up to planing speed easier than a short wide board. Once planing, however, the wider board should stay planing longer in lulls.
I think!
