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light wind surfboard vs foil board

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Peter_Frank
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Re: light wind surfboard vs foil board

Postby Peter_Frank » Mon Feb 19, 2018 12:07 pm

No offense, but you will find out with more experience, that volume matters :wink:

Volume makes a big difference in terms of "how low can you go", when you explore the utmost low end on a hydrofoil, standing fully "parked with zero speed" occasionally, with a given kite, trust me :thumb:

I stick to the statement, that it is all about keeping the "transition energy needed" from non foiling to foiling as low and short as possible, thus flotation is good when trying to get moving from a standstill :D

Having the same area, one superthin no volume, the other lots of volume, there is no comparison whatsoever, and you will be able to go a lot lower with the volume board, as you dont waste energi getting to the surface first, and when out in marginal winds where you need many loops, full stops, and pumping and redirections and so on, to start foiling, it really matters that you got volume.

Of course, WHEN we are up riding/planing no matter if a TT or a hydrofoil, volume makes absolutely no difference whatsoever - but that is a totally different issue, and it seems to confuse as these are two different aspects.
Sub planing on a TT if even the slightest forward speed, volume doesnt matter much either, agree.
But it matters for extreme marginal wind hydrofoiling with a given kite, is my statement and experiences.

8) Peter

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Re: light wind surfboard vs foil board

Postby PullStrings » Mon Feb 19, 2018 1:48 pm

Depends where the volume goes...i'm 77 kg

For example my LW surfboard 5'2" x 21" x 2 3/8 " Quad 4 1/2' front 4' back diamond tail double concave

If you make that board with same dimensions and add volume by making thickness 3 3/8" i will not have more low end to be able to plane earlier

But increase the volume by keeping the center at 2 3/8" and make the length 5"6" and width 25" then you will see earlier planing on waterstart kite downstroke

You would drop your low end of the board to plane by about one knot from 8kn to 7kn with a 17 sqm kite

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Re: light wind surfboard vs foil board

Postby matth » Mon Feb 19, 2018 2:27 pm

Matteo V wrote:
Sun Feb 18, 2018 3:35 pm
matth wrote:
Sun Feb 18, 2018 5:37 am
Larger volume will plane sooner without question because it has more float , but low volume is more manageable once planning.
Again, this is the misconception that almost all windsurfers carry over to kiteboarding. But even in windsurfing, volume over anything that floats with just a bit of freeboard is luggage at sub planing speeds - even on a shortboard. This excess volume IS helpful when displacement windsurfing as it adds stability when a rail is pressured at these non-planing displacement speeds. But once the force of the water pushing up on the (sub)planing surface, even at sub planing speeds, becomes the dominant force holding the board up - volume is no longer a part of the equation.

The best way to conceptualize this is if you have a completely cut away deck down to the bottom layer of the board (no volume) and you start moving. Once you are moving, the water on top will fall off the back of the board and only planing forces will be holding the board up. Obviously this will not work in windsurfing, but it does work in kitesurfing. And it happens all of the time with TT's. Look down at you TT next time you are slowing down to a crawl. There is no volume there, so only the planing forces are working to keep the board up.

Volume is displacement and for displacement to have an effect, the volume must be submerged.
But its harder to sink more displacement/volume which means more float, which equals earlier planning or riding through lulls...

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Re: light wind surfboard vs foil board

Postby Matteo V » Mon Feb 19, 2018 3:43 pm

matth wrote:
Mon Feb 19, 2018 2:27 pm

But its harder to sink more displacement/volume which means more float, which equals earlier planning or riding through lulls...
Again, float is only due to displacement at zero speed, AND ONLY when the board is sunk. If you have any movement, you are not using any of the displacement, but rather planing forces.

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Re: light wind surfboard vs foil board

Postby kitejumping » Mon Feb 19, 2018 3:54 pm

I wouldn't consider 10 knots lightwind at all, if you have a really big kite. A 20m PL Aero or 21m sonic race will have you doing big floaty jumps on a 130tt in much less wind if you know how to fly it. The upper end on my 20m aero ultralight is like 14 knots lol.

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Re: light wind surfboard vs foil board

Postby Peter_Frank » Mon Feb 19, 2018 4:11 pm

kitejumping wrote:
Mon Feb 19, 2018 3:54 pm
I wouldn't consider 10 knots lightwind at all, if you have a really big kite. A 20m PL Aero or 21m sonic race will have you doing big floaty jumps on a 130tt in much less wind if you know how to fly it. The upper end on my 20m aero ultralight is like 14 knots lol.

Agree - and this was the OP's question yes, something for 10 knots, but if you havent much experience in this, you dont know that 10 knots is quite some wind indeed, in hydrofoil terms :D

I can happily foil with an 8 m2 LEI in 10 knots (eventhough I would choose a 10 m2 in this wind), and with a really good light foil kite around 5 knots is possible.

The same goes for good 15-20 m2 big foil kites and TTs, you can ride easy in 10 knots.

8) Peter

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Re: light wind surfboard vs foil board

Postby Matteo V » Mon Feb 19, 2018 4:59 pm

So how about my explanation of the mast being your "edge" or "rail"??? Would you say that is an incorrect statement? Again, the transition from laying in the water at the start, to riding takes place without ever "standing still" on the board. (sub)Planing speed starts the instant you get pull from the kite for me and any other hydrofoiler I have ever watched. - Hood River and Rufus are where I observe other hydrofoilers.
Peter_Frank wrote:
Mon Feb 19, 2018 12:07 pm
.....standing fully "parked with zero speed" occasionally, with a given kite, trust me :thumb:

I stick to the statement, that it is all about keeping the "transition energy needed" from non foiling to foiling as low and short as possible, thus flotation is good when trying to get moving from a standstill :D
Sinking the volume of the board - going from planing forces to displacement force - is a huge waste of energy - at least to get back to planing from that displacement mode. A submerged board has much more surface/sub-surface drag, than when you are just at the sub-planing stage. I have a hard time believing I have never seen this if it is a real thing. Is there a video of someone with good hydrofoiling skills STOPPING and standing there in light winds while the submerged displacement keeps them up out of the water for a 4 second count/ kite parked? And again, how would this be necessary or desired to give up that energy?

Peter_Frank wrote:
Mon Feb 19, 2018 12:07 pm
No offense, but you will find out with more experience, that volume matters :wink:
And none taken. I appreciate when someone can stick to their argument without resorting to logical fallacies such as "Straw man" or "Ad Hominem". As I do not see any of those presented to me yet, I definitely could be missing a piece of information on the mechanics of the hydrofoil board volume issue. I have been wrong before, and I could be wrong either now or in the future.

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Re: light wind surfboard vs foil board

Postby Slappysan » Mon Feb 19, 2018 8:14 pm

Matteo V wrote:
Sun Feb 18, 2018 11:08 pm
With a kite, it would be an almost insurmountable task to go from hip deep to the surface with the board while managing the kite pull (light winds). Think of having inflated balloons for booties. The buoyant force at your feet is very unstable.
Now think about doing it while holding on to a magical rope from the sky, or ... a kite. The kite gives you all the stability you need. Perhaps you think the kite is parked in these situations, it is not. You'll typically be flying it back and forth to generate lift and provide stability.

I think you think it's a lot harder than it is. I routinely sink my board in lulls without falling in.

I know you ride a LF kitefish so you wont experience this with that board at all because it weighs a ton and is pretty low volume. If you have access to a light weight 35L + board take it out and practice standing still on top of it and see how much kite force you need to stay dry.

When you ride boards like this and the wind lulls out you get that typical sinking feeling at first but then the buoyancy will kick in as you slow down and you'll find it reaches an equilibrium where on a no volume board you would have just sank.

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Re: light wind surfboard vs foil board

Postby bragnouff » Mon Feb 19, 2018 8:23 pm

I think what PF mentions when saying volume matters is a buoyant board that is still "reasonable", and that still allows to be angled in the water for waterstart, and pushed against effectively. I'd say maybe around 50L as a max, probably more like 35L. Unlike a SUP, which is just too buoyant for allowing that angle of opposition, and stays too flat on the water for you to push against it and maintain line tension.
In between power spikes at the start (the kite pulls only on a tiny part of the loop, or only on the downstroke), some volume will prevent the board from sinking too fast or too deep, it'll help keep the nose up out of the water, and allow for the upcoming power stroke to be more effective, until you've built up some speed to reach planning/foiling.

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Re: light wind surfboard vs foil board

Postby tautologies » Mon Feb 19, 2018 9:17 pm

This is a pretty interesting, albeit super marginal discussion. I can see both points on which I have thoughts..but of course I can be wrong / missing pieces.

I can go either way..if just standing on the board is the way you go to start floating up, then sure volume matters. On the old raceboards this was pretty key, but the fins where correctly angled when standing on it. Personally at this point I would prefer a low volume board for two main reasons which will kind of explain my approach and speculation.

Having a low volume board allows you to be in the water and so as you angle the board and drift with the wind, the foil will create a bit of lift for the board earlier which allows for a tad more pressure on the kite and and lift from the board. Basically you might be more efficient in terms of generating apparent wind and apparent lift from the foil as the water starts moving across the foil. If you are standing on the floaty board you will miss this and the pressure on the kite will decrease. Obviously I do understand you can angle a floaty board as well..but then why have the volume? ....and some will be able to stand on small board...even when the board submerges to start creating lift...there is a tradeoff point a place which I have no idea where is.

Of course the main reason for me to choosing a small board is I just find it easier and simpler to deal with both for travel and for keeping around.


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