Kamikuza wrote: ↑
Thu Mar 08, 2018 9:53 pm
It doesn't scale in a linear fashion. 10%, or 20% or whatever more weight isn't going to be overcome by the equivalent amount of area in a kite, even if you used the same gear.....
No, but it does scale. And I never said it was linear.
Using windsurfing as an example: nearly 100% of the windsurfing sail area was presented to the wind and produced lift (sideways pull in windsurfing). So the difference in sail area of a 7.5m vs a 6.5m windsurfing sail is 1m. That is a fairly linear relationship given similar aspect ratios on the same model of sail (cord length, camber line, and thicknesses play a huge role if not controlled for in different sizes)
Kiteboarding kites are different in that the projected area (not always published) is much less than the flat area (how kites are sized). Flat area is the size you are told the kite is, or rather what the kite is marked. C vs bow, bow vs delta, and a host of other variables come into play too. But projected area is the most important single factor. If I were told to give the 2 most important factors, it would be projected area AND aspect ratio. Three??? (now we are getting some real info) - Projected area, aspect ratio, and foil camber line.
But for basic comparison, you need to know at least projected area of the kite while it is in flight. Look up the Switch "Element 6" under the "Specs" Section. Inside of the "Details" chart, you will find almost all of the important specifications for a size comparison under a single model. In this chart:
10m flat area kite has the projected area of an approximately 6.5m (actually 6.57) windsurfing sail
12m flat area kite has the projected area of an approximately 7.5m (actually 7.88) windsurfing sail
And here is the main explanation of why windsurfing quivers went in 1m increments at this size range, and kites go in 2m increments.
So to scale off the number on the side of the kite is not a relationship that you could call linear. You have to look deeper in the specs to get close to something that is linear.
And no, you could never actually reach a directly linear relationship, no matter how deep in the specs you go. Pretty soon, you get down to how the designer scaled the different sizes. And there many examples of kites in the past that had size "scaling issues" or rather, good kites in the bigger sizes, but terrible kites in the smaller sizes, and vise versa.
So now that I stole a little bit of your life in that TL;DR,.......if you weight more, go another size up with the kite or the board, or both. No need to get into charts when you can just go bigger and try to make that work.
Kamikuza wrote: ↑
Thu Mar 08, 2018 9:53 pm
You mean about the lines, they stretch under load? Is that really a thing with pre-stretched lines or are the 800lb lines just stiffer?
You should have experienced this when tuning your line sets. Anchor the lines off to something solid like a tree. Pull on those lines and see how much stretch you can feel. Now think about how much bar travel that equates to. Want to see some serious stretch??? Hook your harness up to a line and put all of your body weight on it. You will see some large movements that are very much plausible with that experiment as your kite is actually lifting you up off the water and loading more than you can ever pull on the lines horizontally on land. Want to go deeper? Try to make some crude measurements and test your 800lb front lines (Slingshot) vs your lower test 600lb back lines while hooked to the harness. That is pretty eye opening. And all of this movement due to stretch is equal to bar movement (pulling in the bar when stretching front lines) that powers up your kite. If you had very stretchy (elastic) lines, the kite would be uncontrollable in gusts and difficult to use all around. Want even more stretch? - make your lines longer so that a given percentage stretch equals more length of stretch (and more movement on the bar).
So the more (elastic) stretch in your lines, the less control you have over your kite powering up in a gust off of front line stretch alone.
Your reference to "pre-stretched" lines is talking about a different phenomenon - there are 2 types of stretch, elastic (springy, rubberband) and inelastic "creep" or yield (permanent deformation, like stretching a plastic grocery sack).
The elastic stretch (rubber band) of Dyneema/Spectra kite lines is only controllable by up-sizing the line size (going from 600lb to 800lb). This keeps the load to a lower percentage of the maximum load a line can handle when you up-size. This keeps your kite lines from being too springy like a rubber band.
Inelastic stretch is controlled for by "pre-stretching" Dyneema/Spectra kite lines for a given time at a higher load than they will receive during use. I build my own kite line sets and have lots of experience getting the inelastic stretch out of the lines. By pre-stretching with effective techniques, you can control for yield that would detrimentally effect tune or actual line length.
Want to think about an interesting "paradox"?? A light weight rider on 600lb lines will experience less powering up of the kite due to front line stretch than a heavier weight rider on that same kite. This is because the lighter weight rider has less inertia to resist the powering up of the kite due to line stretch and thus is "yanked" before the lines stretch even more to sheet in the kite...even more. But this kiter did get yanked at an earlier time than a heavier rider, so they may report that the kite is too big anyway. But the heavier rider experiences more line stretch, and thus more stretch induced "sheeting in without moving the bar". But having the inertia to resist this, the heavier kiter may not yet say that the wind is too much. The paradox is that the heavier kiter is stretching their lines more than the lighter kiter, but is ok with it.
Essentially, a 45kg kid can use 300lb lines and experience the same line stretch that a 90kg rider would on 600lb lines who would experience the same line stretch that a 110kg rider would experience on 800lb lines.
Again, at 100kg, I find that 800lb front lines are essential to my comfortable riding as they help to minimize this elastic stretch that powers up the kite in gusty conditions.