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Small vs large foil board

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davesails7
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Re: Small vs large foil board

Postby davesails7 » Sun Oct 29, 2017 3:48 pm

BWD wrote:
Fri Oct 27, 2017 6:02 pm
What about volume? 10-12L seems enough to float almost any foil so it won't sink, but gives challenges starting in light wind. Double that and the sinking when starting will be slower. If the board has a wide shape, it will also sink more slowly, even if volume is not great. To me volume seems even more dependent on taste and specific use than shape, and definitely more than surface area, which seems to follow some basic hydrodynamic principles.
I think volume is important for the lowest wind. A planing craft goes from being fully supported by buoyancy (dependent on volume) to fully supported by hydrodynamic force (dependent on area). For a kiteboard, planing starts around 6 knots, but it's not all planing or all buoyancy, it gradually goes from one to the other.

You can get going with no volume at all, but it takes more power to jump up to speed fast enough. When I get to the lightest wind to kite in, I'm usually standing on the board and between loops or dives I'm not moving at all, so volume and the kite are all that is keeping me up.

When getting on plane, the drag is directly proportional to the trim (tail down angle of the board). The longer the board, the more level you can ride it, and the less drag you will get while getting on plane.
revhed wrote: I was referencing SHAPE as posted, but sure like his thinking ala speed boat hulls.
I don't think speed boat hulls are a good place to look for efficiency at getting on plane. They have very high power to weight ratios and designed to minimize drag at super high speeds.

I'm kinda skeptical of the hoover board, but then again I've never tried it so who knows :wink: It makes sense that the skegs on the side make it not yaw, but I don't see why it would make a difference in stability or drag. If the skegs are submerged, they won't affect stability. Stability (Metacentric Height) is determined by the waterplane area. Air entrapment and air lubrication are things that have been tried with limited success on planing boats, but usually it's for high speed stuff. I'd love to give it a try sometime though!

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Peter_Frank
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Re: Small vs large foil board

Postby Peter_Frank » Sun Oct 29, 2017 4:59 pm

Indeed Dave, the huge volume and size, and still being light, makes Bracurus board excellent in marginal winds I would say :thumb:

RH, why would you worry about directional stability when the board is on the surface ???
I would like one that is, as here you dont need a loose board, never - actually good that it has some directional stability when switching feet hugely underpowered not planing.

Dave, I think the "skeg catamarn hull" works for early planing - have had it years ago on windsurf boards.
But agree, difficult to find any fact about it being better or not :roll:

Would really love a board like yours Bracuru, for the ultimate marginal winds - maybe I will contact you about that ?

8) PF

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Re: Small vs large foil board

Postby bigwave » Sun Oct 29, 2017 6:35 pm

I have had the opportunity the year to try some of the newer large area wings from Levitaz(Cruzier) Shinn(P Foil) and the Takuma foil. These wings have changed my perspective on LW riding. Previously I had an Aquera 160 Allround Board then switched to the 155 Pro Race. I thought these volume style board were the best choice in LW because of there floatation. I was using the Aguera wings free ride and Freerace.
Currently I'm using the 145 Shinn Jackson ,a no volume style board. With the above wings, Levitaz Shinn or the Takuma Your on foil with the first dive of the kite. In the case of the Takuma your on foil before your actually standing on the board,The Shinn P is pretty close to that while the Levitaz not on foil quite as fast has by far the best top end.
I'm not talking racing here , but these wings IMO change the dynamic due to there Lift at very slow speeds. Having a volume board will be better in LW and touch downs on a standard size wing for sure.

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Re: Small vs large foil board

Postby fogmeister » Sun Oct 29, 2017 11:09 pm

yes ,i agree with dave ...i think the next evolution will be big wings, that make board size almost irrelevant........and kite size. We have been experimenting with the alpine ulw.....and it flys with any kite in any wind (you can seriously downsize your kite, or stay same size and be seriously jacked!)......makes a bigboard for 3 kts plus obsolete.....for its size its very fast up to 25kts and surprisingly agile, loads of fun and goes through whitewash.
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Re: Small vs large foil board

Postby Horst Sergio » Mon Oct 30, 2017 12:43 am

Hi fogmeister,

my words: 1000 cm² wing with 63 cm span on a 9 m² kite in, rate your self, think about 5-6 knts of wind. Board size of just 95 x 38 cm doesn't matter. On the other hand I gone back to 680 cm² wing with just 50 cm span and a bigger board for now. But for the future plan to use a 88 x 33 cm board, will see if I will need the big heavier wing again, hope not, as the lower span is nicer for freestyle. :)

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Re: Small vs large foil board

Postby fogmeister » Mon Oct 30, 2017 12:55 am

yes horst that kite size and range sounds bout right, have not been able to test 3-6 kts......but Alpine foil claims to do it with the 11m r1v2 with extensions.....straight into the wind! :wink: the ulw being such high aspect sets it apart from other big wings......and its actually 952 square cm.

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Re: Small vs large foil board

Postby revhed » Mon Oct 30, 2017 10:45 am

Peter_Frank wrote:
Sun Oct 29, 2017 4:59 pm

RH, why would you worry about directional stability when the board is on the surface ???

8) PF
There are times when a quick water start in lower winds strapless seems easier with feet on board, board on rail almost 90° to wind and board slides yaw on surface,
board being flat therefore looser feels better to get correct angle downwind, and
also again lowind missing flying transition and,or flying stance change board on surface because the STRUT acts as a LONG fin it already provides certainly enough yaw stability.
But this coming from a guy who has not had ANY TT fins for years, mostly on flat H20 they are NOT needed and upwind better, "looser" just feels SO much better!
R H

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Re: Small vs large foil board

Postby revhed » Mon Oct 30, 2017 11:03 am

fogmeister wrote:
Sun Oct 29, 2017 11:09 pm
big wings, that make board size almost irrelevant........and kite size.
it flys with any kite in any wind
Been flying a 900 cm2 F wing for 2 years now, of course bigger allows less wind!
Do like the idea of greater A R!

An apple is an apple
a banana is a banana
see new CNN advert for explanation...
Seems these days one can say, post, tweet all out falsehoods and goes unchallenged :o

" big wings, that make board size almost irrelevant........and kite size"
the key word "almost" makes this statement OK.

" it flys with any kite in any wind "
This statement is simple false, not true, a lie... :nono:

NO ONE will KBHF in 4 knots with a 2m2 kite.... :roll:

R H

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Re: Small vs large foil board

Postby fogmeister » Mon Oct 30, 2017 1:12 pm

......its called an expression.....to illustrate a point....hammer it home (but not using a hammer or a home), sometimes on internet its to easy to misinterpret what is trying to be said or say something correctly so everyone gets it in the first place............but its all good! :cheers: :wink:

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Re: Small vs large foil board

Postby flaps1111 » Mon Oct 30, 2017 2:39 pm

Volume is not only good for early planning if you are using a foilkite volume is a must if your kite goes to the drink to use it as a floation device. It drifts better as well on the water when you lost the board. Saying that I prefer a no volume board when is not too Light, I have both 130cm carbon board and a carbon raceboard 145x55.

People talk rubbish when they say they can ride with a non-special kite for lightwind. 8 knots is not light wind, 3-4-5-6 knots is light wind in hydrofoiling.


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