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Raceboard bottom shape

Posted: Mon May 07, 2012 8:02 pm
by ChristoffM
I think the production rules are limiting race board innovations a bit, but seeing that I have no race able events near me and that my first home made kite board came out better than I thought it would, I think I might experiment some more.

I want to do something to the front of the board to minimize the impact when hitting high chop with the nose/front part of the board. I find that coming downwind in chop that is high but spaced close together that I hit the oncoming chop with the front half of the board quite hard and it's uncomfortable and I think breaking my speed a bit. I am thinking of adding a vee to the front.

What I think to do is have the back half flat as per usual, then start a vee where the rocker starts and make the vee more pronounced towards the nose. Hopefully this will spill water to the side when the board hits the water with the front part. Any ideas what a pronounced vee would do to the board there?

The other option I thought of was going for a very deep concave in the front. I initially though that maybe the wind through the concave going to the flat part would help lift the board over the water and lessen wetted surface area. But most of the time the board only skims the top of the chop, so half the board is not touching water anyway, and this air would help nothing. The concave will mean that the front edges could catch chop on the rails throwing one off balance so my current thinking is to go for the vee rather.

Any thoughts from anybody playing with race boards? Of course this is a 70cm wide three fin design.

Re: Raceboard bottom shape

Posted: Mon May 07, 2012 9:05 pm
by Gebi
I built over 20 race boards and vee is not good. Had a lot to do with the shape of the latest Zajicek race board which seems to be going the best when powered by top riders like Hieneken, koch, lake, etc. These guys train hard!!

If you add vee make is super small (less than half an inch)otherwise the board will steer all over the place every time it hits a piece of chop. No fun to ride down wind. If the board is hitting hard you need to tune the rocker line and the balance the power of the fins/strap positions. its all about balance.

Hoping to save you from the experimental stage. I built a few with more vee and they smoked upwind, but were unridable down wind. Even tested with Hieneken and Farley, Farley can ride anything downwind fast; and anyone else, could not ride it downwind!! Funny to watch though! All you saw were the whites of their eyes!!

Re: Raceboard bottom shape

Posted: Mon May 07, 2012 9:43 pm
by BWD
:idea: belly/spoon... ??

Re: Raceboard bottom shape

Posted: Mon May 07, 2012 10:18 pm
by gbleck
You could try to do that with rail shape. I added more V in the front rails on my build. Same thought as you as Lake Michigan has a lot of short period chop. For that matter it's quite close to the sea of coartez in size. Not sure how it rides but that's more of a problem with me not being all that good at ou know... riding.

Re: Raceboard bottom shape

Posted: Tue May 08, 2012 4:51 pm
by ChristoffM
Awesome, thanks for the advice. 20 boards already- wow. This will only be my 2nd racing board.

I will definitely change the rocker line this time, since my first attempt came out horribly wrong. Any idea what amount of rocket I should aim at? 10cm 15cm?

What would you recommend for the front bottom shape? Totally flat like the back, or is this not a good idea? Maybe some concave, or slight belly?

On another note- does anyone know what good the pointed tail shape does. I see the 2012 north board probably has the most pronounced pointed tail, but I cannot figure out what it would be good for, other than having a footstrap further back for downwind riding. Maybe it makes the transfer from one edge of the board to the other softer, giving one more "feel" when trying to keep the board flat?

Re: Raceboard bottom shape

Posted: Fri May 11, 2012 11:31 am
by Hollow
Does anybody tried a rounded bottom shape in the front? Somethink like that in the cross section picture. It is a compromise between flat and vee. It would prevent from steering and reduce impact.

Re: Raceboard bottom shape

Posted: Fri May 11, 2012 3:35 pm
by ChristoffM
Well, I am going to make my second race board and hopefully get it much better (not that the first one rides badly at all).

I like your rail shapes. Its what I had in mind, but less belly in the front. Flatter, but of similar shape.
Is the middle size the mid section rail shapes? It looks too round to me? I think it should be square by the middle already? Looks good for 25% from the front I think.

Re: Raceboard bottom shape

Posted: Fri May 11, 2012 4:23 pm
by Hollow
No. The last section is somewere in the middle. Mid section is 0,5 meter from the nose. And the highest is the tip.
Will you go with 10 cm rocker in the nose?

Re: Raceboard bottom shape

Posted: Fri May 11, 2012 4:55 pm
by ChristoffM
10cm would make my job easier, but it seems too little to me. I am going with 14cm at the nose. GBleck's rocker has this, and the best picture on the net of the north 2012 board when scaled seems to be 13 or 14 cm. And I am putting 9mm rocker in the tail, with the thinking being that it will allow me to keep the nose higher when going down big chop so that the board is at a better angle to fly over the oncoming chop. Then the front of the board can be totally flat, but with the rails as in your picture.

Re: Raceboard bottom shape

Posted: Fri May 11, 2012 11:56 pm
by tautologies
How about a keel of sorts? Instead of a vee, make it a 2 inch keep going from front to back, then have a cut off at the back. Intuitively I think this makes sense for very choppy conditions. I think it is weird if the same board that works for ultra light wind and glassy conditions is the same that works for windy and choppy conditions.