Why do I need a much bigger board AND bigger kite for a heavier rider?

[Mossy 757]

The energy content of the wind increases exponentially in a direct relationship with velocity, so at the light end of the spectrum there's a larger percentage increase in equipment than at the higher energy content end of the spectrum.

[grigorib]

What rider(s) weight you consider kite quiver for?

What is a 170lb guy riding? - 12m

So I weigh 225lb, and need to upsize at least 1 size to 14m or go to a 15m.


But what if you are skilled at light wind or just use smaller kites than almost all the other kiters?

Then try the 12m.


It's not "rocket surgery" or "brain science". And you all know how in depth and detailed I get on the academics. Even I just guess on this question and go for it. The "academic reasoning" behind me just guessing is that you can use a range of kites in a given wind speed which will yield different performance curves for specific applications. If you can only do 1 trick, or focus only on 1 application for the kite/rider/board system, then figuring out some equation may help you. But the rest of the kiting world boosts when overpowered (picked too big of a kite), or carves hard when underpowered. There is lots to play with when things are not "just right".

and consider that different models/years/brands sizing is also different and not exact.

[edt]

Does not make sense to me to have 87% increase combined for only 26% increase in weight.

I would say for 26% increase in weight I might want say 13% increase in surface area and 13% increase in kite size?
13% increase in surface can be something like 135*45 cm (compared to 135*40)
13% increase in kite area is going from 10m to 11.3m .

My understanding is this somehow above increase values are actually not enough?
Correct? Why? Where did I go wrong?

Why most people suggest 20-25% increase in board area plus 40% increase in kite surface
????????? LOL

Absolutely correct!

I think math is not a kiter's strong point. Generally though what happens is you usually want to increase both the kite size to some degree and then increase the board size a little too exactly as in your example, I like the 13% and 13%.

What happens (because kiters generally are bad at math) is that we get these certain fixed points where we know that they work. for instance someone might just happen to know that their students in 20 knots wind weighing 60kg does fine on 7m kite with a 125cm board, while a rider weighing 100kg does fine on a 14m kite with a 140cm board. So they figure hmmm 67% increase in weight means 100% bigger kite and 12% bigger board but the math isn't like that!

A huge monkey wrench is the fact that people ride boards different. A small kiter might like a big board and a big kiter might like a small board or vice versa. Board size is such a personal preference. Kite size is a preference too, just how powered do you need to be to have fun?

Anyway, I like your math, and don't worry too much about what people say, they don't always get the math right. Remember even though the force is proportional to the velocity squared that's only the wind speed! We should talk only about linear differences in kite size and board size. When you are talking about two kiters both kiting at the same wind speed, with for instance one kiter weighs 60kg and another kiter weighs 100k that means you can either have a kite 100/60 times bigger, or you can have a board that is 100/60kg times bigger or some combination of the two. The square doesn't come into account until you start varying the wind speed so we don't really to calculate the square here as it's just one of the givens variables. We assume we already know what either the 60kg rider or the 100kg rider is riding. So to figure out what the rider we don't know is riding we only need a linear factor. If we don't know what either rider is riding at 20 knots and only know what they ride at 15 knots for instance then yeah that's when you need to do a square or square root of the velocity of the wind.

[Matteo V]

Step 1: Find all the variables
Step 2: Find an equation to put them in
Step 3: Do the math

The problem here is you can't get past step 1.

If you get inconsistent answers from the variable set you consider to be accurate, you are either missing variables, have the wrong values for some of those variables, or have the equation or math wrong. Please stop digging.


15kts of wind NNW on the beach at my current location means that you could have 25kts on the outside, or 13kts on the outside with gusts to 35kts, or 10kts in the break with 12knts on the outside with gusts to 18kts and lulls to 3kts. That is for 15minutes of a 5 hour session. Then it changes. Unfortunatley, I am not fast enough to walk in, land the kite, take down the kite, pump up a new one, launch again, and walk back out in 15minutes.


And if we want to start playing "name that variable", then how about the rocker of the board? or the concave? How do those things affect your effective surface area vs projected surface area?

[sergei Scotland]

What is a 170lb guy riding? - 12m

So I weigh 225lb, and need to upsize at least 1 size to 14m or go to a 15m.

Cool, thanks.
14/12 = 1.166 (16.6 %). Not 13 as I estimated but close enough. 25% for 15/12=1.25
Thanks.

[sergei Scotland]

Step 1: Find all the variables
Step 2: Find an equation to put them in
Step 3: Do the math

The problem here is you can't get past step 1.

Sure, absolutely agreed. No one can find all the variables. A bit like big models (like climate models for example).
Put it this way - if I put on 20 kg of lead weight on the same 75 kg boarder - what should increase in board and kite size be (the same kite and board make/variant)? Roughly as an educated guess?

Also - my original question was "why", not "how much by".
I had the impression that on the same spot, with the same board and the same kite I need to go 25% up on the kite size AND 25% up on the board size for 25% increase in weight.

Looks like this is not the case though - i.e. 15% + 15% or even less should do it as everyone seems to think.

Thanks!

[deniska]

Well, befinners are inefficient and they start with larger sizes.
Then they can ride well
Then there comes that phase of “I can ride smaller than anyone else” that day
Then they need more and more power to boost
Then they need slightly smaller size again to loop and turn fast

then you get good at foiling and realize that you can ride any kite from 7 to 17 on any average 9-20kts day

[grigorib]

Well, befinners are inefficient and they start with larger sizes.
Then they can ride well
Then there comes that phase of “I can ride smaller than anyone else” that day
Then they need more and more power to boost
Then they need slightly smaller size again to loop and turn fast

then you get good at foiling and realize that you can ride any kite from 7 to 17 on any average 9-20kts day

Not quite that generic...
First you ride a regular size or something smaller than regular
Then you can ride very, very small sizes
Then once you can edge hard you can ride large sizes again
Then you debate - to take a small kite and large wing or larger kite and a smaller wing. Speed or surf question
But as a freeride foiler you can’t stand anything above 12m. After a while even 9m seems slow
You sell your LW 15m and you largest wing is 11m

But all the time you ride 1/2-2/3 of size of guys with a wakeboard

And then windsurfers wonder in shock when you boost on 9m in 30 knots on a wakeboard, next day fly the foil on 9m in 18 knots and then cruise a large surf foil wings on the wry same 9m in 8 knots.

[slim_charles]

Stupid question?
I am only asking because lift/water resistance is proportional to square of speed and only linear with surface area, i.e. lifting force is:
F = k *v*v*S
where V is speed and S is surface.
General rule of thumb seems to be 135x40 for 75 kg rider 150*45 for 95 kg rider, correct?
Plus 9-10 m kite for 75 kg and 14m for 95 kg for the same conditions.
So kite roughly 40-50% more powerful required plus+ board surface area 1.25 size of smaller board.
So for only 26% increase in weight (95/75=1.26) people recommend 40-50% increase of pull PLUS 25% increase in board surface area? 1.5*1.25=1.875 - i.e. 87% combined kite + board increase...
Does not make sense to me to have 87% increase combined for only 26% increase in weight.

I would say for 26% increase in weight I might want say 13% increase in surface area and 13% increase in kite size?
13% increase in surface can be something like 135*45 cm (compared to 135*40)
13% increase in kite area is going from 10m to 11.3m .

My understanding is this somehow above increase values are actually not enough?
Correct? Why? Where did I go wrong?

Why most people suggest 20-25% increase in board area plus 40% increase in kite surface
????????? LOL

Forget all the above... its meaningless. The only way to understand is to try, ditch the calculator, grab some boards and get to the beach!

[andrewjohn]

Stupid question?
I am only asking because lift/water resistance is proportional to square of speed and only linear with surface area, i.e. lifting force is:
F = k *v*v*S
where V is speed and S is surface.
General rule of thumb seems to be 135x40 for 75 kg rider 150*45 for 95 kg rider, correct?
Plus 9-10 m kite for 75 kg and 14m for 95 kg for the same conditions.
So kite roughly 40-50% more powerful required plus+ board surface area 1.25 size of smaller board.
So for only 26% increase in weight (95/75=1.26) people recommend 40-50% increase of pull PLUS 25% increase in board surface area? 1.5*1.25=1.875 - i.e. 87% combined kite + board increase...
Does not make sense to me to have 87% increase combined for only 26% increase in weight.

I would say for 26% increase in weight I might want say 13% increase in surface area and 13% increase in kite size?
13% increase in surface can be something like 135*45 cm (compared to 135*40)
13% increase in kite area is going from 10m to 11.3m .

My understanding is this somehow above increase values are actually not enough?
Correct? Why? Where did I go wrong?

Why most people suggest 20-25% increase in board area plus 40% increase in kite surface
????????? LOL

Forget all the above... its meaningless. The only way to understand is to try, ditch the calculator, grab some boards and get to the beach!

Totally agree. I’m nearly three stone lighter now than when I started kitesurfing, but I still use the same kites in the same wind ranges, but I can jump higher. That’s the only difference I’ve noticed.
The biggest thing for me to eek a bit more wind out of a kite is to have a very wide board for when conditions are marginal.