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Difference on the small foil boards..

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KVL
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Difference on the small foil boards..

Postby KVL » Sat Oct 06, 2018 5:01 pm

Hey,

I have been looking into several of the new smaller foil boards, e.g. Moses T38, Crazyfly F-Lite, Groove Skate etc.
Common is that they are all made of carbon, around 120 cm and around 2.4 kg.
All of the boards - I believe - are aimed more or less to freeride, primarily strapless, with larger fins..

Some of them are fat sandwiches on 4 cm (T38), others are only 1.5 cm (F-Lite), some has a little rocker (in front) (F-Lite), others massive (Groove).

What for and against are there on these big differences in parameters - what is the coolest and why?

I cant decide - personally I would prefer the very thin one, but not sure why, or what I am loosing if not going with a fatty or rocker one..

All the same or great differences?

Thanks, K

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Peter_Frank
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Re: Difference on the small foil boards..

Postby Peter_Frank » Sat Oct 06, 2018 6:49 pm

Heavy nose scoop (nose rocker) means you can touch down ever so hard without submerging and crashing, a huge advantage.
Another benefit is your stance, you can stand with both feet comfortable and straight (or at least bent the same).
If using a flat board, the board has to be tilted a tad up otherwise will it otherwise nosedive even before you start, if really short.
When tilted a tad up, you have to stand with your front leg a bit bent always, when rear leg is straight.

Downside is, you lose some of the early planing when board is on the surface, when not flat.

Thickness, yes, just like you "feel" a thin board feels good when on the surface and okay power to start, just like a thin surfboard feels much better.
And when using it in waves, with a thin non-voluminous hydrofoil board it is much easier to traverse the waves when dragging out with the board "through" or under the waves, even really small wind waves.

But a thicker board has many advantages - can be made superlight and still stiff, will get more fragile so you should not drop it on something hard, but it will be a much lighter and stiffer board thus much better when riding.
And you wont sink if a huge lull comes by, and you get better lowend for getting up to foil, so here volume means a lot.

On the other side, you use these short boards when sufficient wind usually, so if you got a light wind board too then you probably want the thin board.

These are the ups and down I know of :D

8) Peter

I prefer this rockerline, my KETOS 118 with the lovely extreme noserocker:

Pocket118.jpg


And the Groove has a quite similar rockerline:

GS.jpg

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Re: Difference on the small foil boards..

Postby Qiter » Sat Oct 06, 2018 7:16 pm

I agree with all of the above. Another reason to consider is safety ( I own a Moses T40 and a T38): I use the T38 when I am sure I can easily relaunch the kite (9kn+) and the T40 in marginal conditions with no relaunch possibility, when the chance of a swim is on the charts (usually 6-9 kn with a 12m LEI). Reason being that the T40 comes out of the water earlier (with the same mast and wing) and I can sit on it and drift back to shore and not worry should I drop the kite.

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Re: Difference on the small foil boards..

Postby TomW » Sat Oct 06, 2018 10:27 pm

Pocket board in 2 to 2,5 kg range has huge impact on foil behaviour.
I built 2 boards, one is 120cm x47 the other 135 x 47. 300g difference. The 15cm difference is 75mm taken off tail and nose in relation to the mast. Huge difference in agility on same foil.
I can't figure out how it has such a huge effect. It defies common sense of physics.

TomW
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Re: Difference on the small foil boards..

Postby TomW » Sun Oct 07, 2018 1:08 pm

Changed from my 135 to 120 board today and first went out on 590 wing. Easy enough to get going. Then went in and changed to 633 wing because there was seaweed.

Both wings are much less pitch stable and more agile on small board.
Hypothesis: the wind is pushing on the board causing some sort of stability, Or it's the extra weight .

But 300 g total ?? And 150mm length?

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Re: Difference on the small foil boards..

Postby BWD » Sun Oct 07, 2018 3:29 pm

I think it’s about cg.
Cg of a foil is usually “in” the mast closer to the foil than the mast plate or top. Cg of a board is in the middle of the board. Cg of the total is on a line in between. The longer in front of foil the board projects, the closer to the board, and farther from the foil, the total Cg will be, and the greater the inertia.
Low inertia and cg more in aligned with cg of foil itself means better feel , quick response and less stability.
Maybe it would be interesting to play with adding weight to smaller boards to see if it would make them feel the like longer ones - as long as they don’t sink.
I am sure air pressure on the bottom of the board plays a role too, especially when going fast.

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Re: Difference on the small foil boards..

Postby butterfish » Sun Oct 07, 2018 4:58 pm

i use a custom board fron franz olry (alkita kiteboards) which is 100*43cm, 6cm nose rocker and 1785gr. total weight incl. eva pad. simply perfect!

cnski
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Re: Difference on the small foil boards..

Postby cnski » Sun Oct 07, 2018 6:28 pm

Butterfish- Would love to see some pictures of your board. Please post some!

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Re: Difference on the small foil boards..

Postby butterfish » Sun Oct 07, 2018 8:19 pm

dont know how to post pictures here?! 😬🙃

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Peter_Frank
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Re: Difference on the small foil boards..

Postby Peter_Frank » Mon Oct 08, 2018 5:58 pm

As BWD says it is about inertia.

Not as much the center og gravity as it can be the very same on two boards, but if one is an either longer board, or a heavier board, the moment of inertia (or rotational inertia) is bigger.

Moment of inertia is how difficult it is to "turn" something, so if really low, you got a foil that feels superlight to turn :D

For the very same reason we all know, that if you rotate on a chair with arms/legs out, and bring them in to your body, you will accelerate like crazy :rollgrin:


We turn approximately around the center of effort (COE) on our hydrofoils if we just focus on yaw, COE is around 15 cm / 6 inches in front of the mast on many foils, the point between our feet.

If you got a longer board, nose longer, everything else being equal, even if board total weight is the same, the weight of the nose of the board sit further away from this COE.

The moment of inertia is proportional to the distance to the nose, SQUARED. And proportional to the weight of the nose, but not squared.

Meaning if you have a 120 cm board, the nose is say 75 cm in front of the COE, and with a 130 it is 85 cm away.

If you put the same quite heavy weight (a lot more than the board) on the very nose of these two boards, the big one will feel 28% slower to turn than the 10 cm shorter one.

In reality the difference is a lot smaller, my estimate would be a few percent only, as most of the mass sits closer to the COE, but my point is, that the longer boards will feel rapidly harder to turn because "distance" is squared.
And we humans are extremely sensitive to feel these small differences, so no doubt it can feel like A LOT :naughty:

Having said that, I honestly believe it is also a mental thing, our minds help us feel smaller boards are a lot more agile than they really are sometimes :wink:

My 150 cm board is extremely light, and got almost no weight at the nose, so my 118 and 130 cm boards are not that much faster to turn, but mentally you will most likely get an aversion against the bigger ones, that will multiply any difference hugely, or even ADD a difference, even if there is none ha haa, that is how we as humans work.
Usually there WILL be a difference though, and can be easily felt, the shorter ones, same type of build will be much faster to turn!

In normal conditions I can not see wind on the board having any noticeable effect at all, compared to the moment of intertia which is a huge factor regarding how fast they are (to turn).

So extremely light at the nose, doesnt matter that much at the mast really, and a shorter board gives you the most lively board :thumb:

8) PF


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