‘Drive’

Chat about stuff that doesn't fall into the other categories here.
wully
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Re: ‘Drive’

Post by wully » Fri Jun 07, 2019 6:58 am

Bouke/Witchcraft wrote:
Thu Jun 06, 2019 9:37 pm
Apart from the fins, a flextail which flexes under pressure will get a forward component from that pressure plus a tighter turn. That is why surfers want boards that flex.
I can visualise getting a component of speed when the stored energy is released when the board flexes back to its design shape?

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Bouke/Witchcraft
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Re: ‘Drive’

Post by Bouke/Witchcraft » Fri Jun 07, 2019 11:26 am

wully wrote:
Fri Jun 07, 2019 6:58 am
I can visualise getting a component of speed when the stored energy is released when the board flexes back to its design shape?
Not really, you get the forward momentum from when the tail flexes. A bit like when you squeeze an orange seed and it shoots forward. See image below. Now a board with lots of rocker would do the same but as soon as foot pressure is released, it would start to suck and drag where the flextail flexes bag and does not suck.

Just like in the images of the drive article you can see there are forward "drive" components in the lift the fins generates. Providing the fins are toe-ed in and twist off (not the same as flex, a flexing fin only will result in twist of the fin is raked back). The result is very similar to our sail, which also provides a much bigger side ways force with a little forward component in it, which is enough anyway to keep us planing.
drive from flex tail.jpg
drive from flex tail.jpg (365.86 KiB) Viewed 363 times
Last edited by Bouke/Witchcraft on Fri Jun 07, 2019 11:48 am, edited 1 time in total.
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Re: ‘Drive’

Post by Bouke/Witchcraft » Fri Jun 07, 2019 11:47 am

Ruaraidh_K257 wrote:
Thu Jun 06, 2019 10:45 pm

Your KS3s will give you a lot of drive off the bottom turn I think and then go neutral on the top. So in theory they should generate lots of power when you get to the bottom of the wave and start to carve uphill, then lose it at the top of the wave when you have plenty of speed. Likewise my Combats provide continuous drive rather than on off, making them more useful for waves that don’t have much power etc

I think!
Yes, you get sails that drive more or less. This depends on the profile depth and centre of effort. A higher centre of effort results in more mast foot pressure, which results in more power in the rail as Andrew Fawcett puts it. But you have to be aware that when the sail does not get the wind entering on the mast side, it starts to behave quite differently. As long as it enters the stiff, mast side and leaves the soft leach, the sail is more or less self regulating. When the wind is straight from behind or even entering the soft side, things turn around, the softer the leach, the harder the sail is to control. And profile stability depends on 3 things: the nr of battens, the quality of the batten profile and seam shaping. If there is no or little seam shaping and the quality of the batten profile is not that good, the profile starts moving about, which is hard to keep under control when you are in a in a bottom turn and you can´t just sheet in or out as we use the sail to help turning.
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Re: ‘Drive’

Post by wully » Fri Jun 07, 2019 7:43 pm

I like the orange pip analogy!

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Re: ‘Drive’

Post by GraemeF » Sat Jun 08, 2019 4:46 pm

OMG don't you just miss basher sometimes, I'd love to have seen his reaction to that illustration, meanwhile I think I'll just reach for that can of BS repellant, now where did I put it, it's been a while since I've had such a bubble bath...


Think I'll get my old Challenge Flex out, that's in the Drive.. :lol:

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Re: ‘Drive’

Post by wully » Sat Jun 08, 2019 7:17 pm

GraemeF wrote:
Sat Jun 08, 2019 4:46 pm
Think I'll get my old Challenge Flex out, that's in the Drive.. :lol:
I hope it’s cemented under your drive - that’s about all those clunky heaps we’re good for - ballast.

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Re: ‘Drive’

Post by Bouke/Witchcraft » Sat Jun 08, 2019 7:49 pm

GraemeF wrote:
Sat Jun 08, 2019 4:46 pm
OMG don't you just miss basher sometimes, I'd love to have seen his reaction to that illustration, meanwhile I think I'll just reach for that can of BS repellant, now where did I put it, it's been a while since I've had such a bubble bath...
Think I'll get my old Challenge Flex out, that's in the Drive.. :lol:
Don´t you use very similar illustrations in sailing class since centuries?

I´d say try it Grumpf but you probably can´t. It isn´t +3m long.

This flex tail has nothing in common with the Challenge Flex which didn´t disappear again after one year for no reason. Back then that meant something. The whole tail could flex in any direction and had the fin in the flexing part which would twist the tail and once twisted, it wouldn´t flex in the right direction anymore. Try a piece of paper, once it´s bend one way, it won´t bend the other way anymore. But were you not the one trying to sell these things to people anyway?
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Re: ‘Drive’

Post by wully » Sun Jun 09, 2019 5:22 pm

Bouke/Witchcraft wrote:
Sat Jun 08, 2019 7:49 pm
. But were you not the one trying to sell these things to people anyway?
He did sell quite a few ‘back in the day’.

I stocked at least three and don’t recall them hanging around on the rack for long - like pretty much all the Mistral stuff I sold.
I’ve got fond memories of the Mistral kit from back then - except the Challenge Flex. That was junk.

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Re: ‘Drive’

Post by Ola H. » Mon Jun 10, 2019 2:14 pm

wully wrote:
Wed Jun 05, 2019 3:54 pm
Describe what ‘Drive’ is for me please?

The term gets chucked around a lot and I’d be interested to learn what others perception of this is....
I will assume you mean the meaning of the term as it is used to describe a particular aspect of waveboards (for windsurfing) or surfboards. I'm not fully aligned with Boukes description from the linked text, in particularly not the first sentence, but from the rest of the discussion I think we might be pretty aligned after all.

I will start by citing Scott McKercher from an old email conversation ages ago. We were actually more talking about different breaks and what boards needed to do to excel in these breaks, but he used two concept that he separated quite carefully. "Production of drive" and "Containment of speed".
Carrying, holding and being able to handle speed is not the same thing as drive. At some places, like Hookipa at some size, the last thing you want is for the board to generate speed when through your turn. But you will have to go super fast and the wave will generate the drive and you want your board to respond gracefully to what the wave gives delivers, not only by handling speed, but also by accelerating fast enough an letting the wave deliver all that energy without the board resisting when receiving it. That is containment of speed.

Drive in a board, is also a matter of how the board responds to forces that is applied to it, but now we are talking forces that the sailor (or surfer) generates when turning as several of you discussed above. The skateboard comparison is actually very good and just like when pumping on a skateboard, in a good turn in some types of waves, the sailor uses a very similar technique to accelerate in the turn which involves coiling up a bit through the apex of the (bottom-) turn and then extending just after. You conserve a bit of the velocity you have coming down right through the apex, then you "release" this velocity in the new direction after the apex. Different board and fin setups responds to this type of move differently. The level of response is the level of drive. Not that it might be sailor and conditions dependent though. Some boards might respond very well to some sailors techniques (and hence be drivey) but might feel dull for others.

There is a third characteristic that is separate from both of the above and that might be called "glide" (or something similar). This is the ability to keep speed when neither the wave nor the sailor produces it.

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Re: ‘Drive’

Post by Bouke/Witchcraft » Mon Jun 10, 2019 5:32 pm

Usually drive is the most important in conditions where speed and keeping speed is not easy. So Hookipa can be pretty much dismissed, control (of the speed) is more the issue there. Windswell spots are also usually not locations where you would notice a difference in drive as to have waves, you need quite a lot of wind. A board with good drive is most needed in spots with lighter winds.

I did not take into account the sailor can use his weight to generate speed because he can do this with any board. The board that will do this better also keeps speed better if the sailor is more static. If the wave has a slow section, a flex tail can be pumped though it like surfers do but a flex tail will get through this better anyway as it goes straighter when moved forward and gets rocker when pushed.

I had a little video from 2011 with various Witchcraft riders at Glass beach which is a typical wave where drive is very important. Non planing and a small wave where you need to turn tight not to out run the wave, you generate speed dropping in and then use that speed for the top turn or aerial. It has Will Ward riding various boards, his own highly rockered board and 2 proto flex tails, one 78L and a 90L. I will see where it is and upload it later. Anyone can guess by the turns which ones are the flex tails. Both Will and Andrew have gone back to normal boards as the flex tails were too easy, it made their technique sloppy.
[yt][/yt]
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