## Monday, January 17, 2011

### Interactive Kiteboarding Calculator

A while ago I posted a table relating kite size to body weight and wind speed for kiteboarding. It starting getting a lot of hits, so I decided to go ahead and soup it up as an entirely interactive kiteboarding calculator, modeled after my windsurfing calculator spreadsheet. It has two pages- one for kites and one for boards, which you can switch between by clicking the "kitesize" and "boardsize" tabs at the bottom. As with any effort to apply simple math to a complicated and subjective thing, it ain't perfect, but it ought to help give less experienced kiters a rough idea about what kind of gear they need.

If you can't view the embedded version, you can download the file here.

Unknown said...

Thanks James!

Checco said...

Hi James, thanks a lot.
I think there should be some adjustment related to the board sizes, since my weight is 96kg, even for "Board for High Powered Riding" it says 149cm length and 45cm wide.

Peter van Amson said...

Nice calculator. I am surprised that a linear formula can capture the relation between wind speed and kite size so well.

James Douglass said...

Shawn- Right on, dude.

Checco- I adjusted the board size equations so it should be a little better now.

Peter- Thanks. I'm sure the actual physics are much more complicated, but the linear approximation seems to fit ok in the range of typical wind strengths and rider weights.

The rockstar said...

Very instructive graph Peter.
Well done!

BTW it will be great to see the how curves change for a parametric board size.
From my personal experience, relative smaller changes in board size make a big difference.
Especially the width of the board.

Can you please show us similar curves for different board sizes?

James Douglass said...

Hey Rockstar- When I made this graph I put board size recommendations on a separate tab of the spreadsheet, which you can get to by clicking "board size" at the bottom of the spreadsheet.
I didn't explicitly link board size and kite size because I think the relationship is a little more complicated than my limited math skills can model. Qualitatively, the effect of board size would be to change the "ideal point" in a kite's wind range. I.e. you can ride more comfortably near the max of your kite's wind range if you use a smaller, narrower board, and you can get closer to the minimum of your kite's wind range the bigger the board you use.

Uli R. Donohue said...

Love the calculator, will test it for real this week on OBX! Thanks!

kiteUp said...

Hello James,

I am developing an android app(KiteUp).
Now i would like to handle kiter weight.

usually on KiteUp the user has to fill in the windrange of his kites. For example:

LF Envy windrange for 75kg person does fly from 10 to 24 Knots.

Wingrange values for all kites are usually for 75kg kiters. But what if my weight is 130kg or just 40.

Could you help me to handle that?

best regards

James Douglass said...

KiteUp- Start with a linear formula relating kite size to wind speed and weight. Kite size is inversely proportional to wind speed and directly proportional to weight. There will be some constant "X" factor in the equation which will be different depending on what units you use for wind, weight, and kite size.

Kite Size = (1/Wind Speed) * Weight * X

Solve for X for the 75 kg case. There will be an X for the upper wind boundary and a different X for the lower wind boundary.

Once you know X you can put in any weight and recalculate the upper and lower wind boundaries.

The only problem is that the lower wind boundaries don't scale continuously with body weight. They are constrained by the fact that the kite needs a certain amount of wind to keep itself in the air, regardless of how light the person flying it is. So for the lower wind boundary you would have to build something into the equation like, "If calculated lower wind range is <8 knots, 8 knots."

Good luck.

kiteUp said...

Hello James,

Thanks for this information. I see it will be tricky. Will try to implement it.

best regards

Unknown said...

Hey man awesome calculator! We dig it. Keep it up man that's gnarly!

Okkite Kiteboarding School
http://www.okkite.com

Unknown said...

Great job.... I want share a kitesurfing school website were kitesurfing lover lern how to launch kite wih proper instruction. http://www.kitesurfingnovascotia.com

Ethan said...

Hi James- Thank you so much for putting this together! It has been really helpful for me as I choose kites as I am much lighter than the "average" rider.

I'd love to download the spreadsheet, but the link appears to be broken. If you'd be willing to email it to me, I would be happy to post it in my dropbox and provide a new public link for you to post on your blog so others can download the file.

Thanks,
Ethan
ethan.waldman[at]gmail.com

The Flow said...

Goshdarnit said...

This is an awesome resource! Thanks. My wife and I are both starting out and this has given some great guidance. Just for your information, the range I get from my 9m Bandit is almost exactly what this table gives. I have now ordered a 6 and a 12 based on your guide. No pressure! ;)

As others have mentioned, the download link doesn't work for me. I really would like to hold a copy of this on my computer and my phone, so would appreciate a working link if possible.

bonerici said...

he uses this formula: knots * 2.175 / weight in kilograms. the real formula is closer to this: (wind speed in knots) ^2 * 2.4 / weight in kilograms

it's NOT a linear relationship there's a square of the wind speed in there he's missing

Kite Obsession said...

Thanks for sharing such an informative post.