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francis luengo
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cutouts wingfoil boards

Postby francis luengo » Mon Nov 15, 2021 6:32 pm

Can anyone explain how the cut-outs work and if they really are efficient?
There are theories that flat stern are faster to take of.
thxs

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Re: cutouts wingfoil boards

Postby StellaBlu » Mon Nov 15, 2021 7:02 pm

The theory behind a tail cutout is that you can "ollie" up onto foil or improve pumping efficiency with the incremental clearance in the tail.

The newer thinking is that any incremental takeoff gain from the tail cutout (not clear if there was actually any gain to begin with) is more than offset by the reduced speed achieved by shortening the effective running length of the board's hull. The new school of thought is to maximize running length so you can get the board up to speed, thereby creating lift to get you onto the foil. The other factor is that some tail kick designs create dirty flow and drag, further reducing speed, while a clean cutoff on the tail minimizes that drag.
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Re: cutouts wingfoil boards

Postby omg » Mon Nov 15, 2021 7:15 pm

Newest board from KT, quite a bit different from other ones.

Image

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Re: cutouts wingfoil boards

Postby StellaBlu » Mon Nov 15, 2021 7:19 pm

omg wrote:
Mon Nov 15, 2021 7:15 pm
Newest board from KT, quite a bit different from other ones.

Image
The odd thing is that the BRM guys have been riding some really nice looking unreleased KT wing boards with a much more conventional shape. Very clean design with no kick tail, no dramatic hull features, no gimmicks. I was kind of hoping KT would just release THAT board. Maybe this thing is great, but there's just a LOT going on and it feels gimmicky.

I think this board is trying to minimize the "thickness" between the foil mount tracks and the deck of the board. Other boards accomplish a similar feat by scooping the deck, which preserves clean flow over the hull.

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Re: cutouts wingfoil boards

Postby windmaker » Tue Nov 16, 2021 3:59 am

All those steps and cuts look like marketing gimmicks to me but I guess some people like that. Question is, If they really make a difference why wouldn't KT (and others) use these shapes on their surfboards/windsurf/kitefoil boards? The answer is they did... many years ago but have now evolved to the simple clean shapes we all know.
In my case, simple is better.

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Re: cutouts wingfoil boards

Postby vol » Mon Apr 11, 2022 10:13 am

KT ginxu explained that this long tail cut help much easier angle board at start and foil wing start working earlier, also same when you touch water board don't stuck and much easier continue

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Re: cutouts wingfoil boards

Postby consumer » Mon Apr 11, 2022 2:41 pm

StellaBlu wrote:
Mon Nov 15, 2021 7:02 pm
The theory behind a tail cutout is that you can "ollie" up onto foil or improve pumping efficiency with the incremental clearance in the tail.

The newer thinking is that any incremental takeoff gain from the tail cutout (not clear if there was actually any gain to begin with) is more than offset by the reduced speed achieved by shortening the effective running length of the board's hull. The new school of thought is to maximize running length so you can get the board up to speed, thereby creating lift to get you onto the foil. The other factor is that some tail kick designs create dirty flow and drag, further reducing speed, while a clean cutoff on the tail minimizes that drag.
best explanation to date! Thank you StellaBlu

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Re: cutouts wingfoil boards

Postby tkaraszewski » Mon Apr 11, 2022 4:00 pm

The traditional reason for steps like this in planing boats or aircraft floats is that while the flotation of the entire hull is required at low speed, once you reach planing speeds, you no longer need so much hull in the water. As the hull rises up onto the forward part, the back of the hull is now up and out of the water, greatly reducing drag. In airplanes, this allows the whole plane to rotate upward by "pivoting" on the step as well, which is great for takeoff.

I'm skeptical of how useful this would be in wingboards. Wingboards don't really plane without foiling (if you think they do, please send me a video), and even though they could benefit from the second point above (being able to pivot backwards), they can only do this once on plane, because the advantage to being able to pivot here is that there isn't water under the back of the hull.

The "ollie" idea implies this is like the kicktail on a skateboard, which only works because there's empty space underneath it. I don't see how it works if the board isn't operating in a position where the whole bottom is still in the water, and I'm not sure such a position exists on a wingfoil board where the foil isn't already working.
StellaBlu wrote:
Mon Nov 15, 2021 7:02 pm
The other factor is that some tail kick designs create dirty flow and drag, further reducing speed, while a clean cutoff on the tail minimizes that drag.
This is well-established in boat design. You want a clean separation of water off the transom for less drag. A step in the middle of the hull is only fast when the front half of the hull is in the water but the back half is not.
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Re: cutouts wingfoil boards

Postby consumer » Mon Apr 11, 2022 4:29 pm

tkaraszewski wrote:
Mon Apr 11, 2022 4:00 pm
The traditional reason for steps like this in planing boats or aircraft floats is that while the flotation of the entire hull is required at low speed, once you reach planing speeds, you no longer need so much hull in the water. As the hull rises up onto the forward part, the back of the hull is now up and out of the water, greatly reducing drag. In airplanes, this allows the whole plane to rotate upward by "pivoting" on the step as well, which is great for takeoff.

I'm skeptical of how useful this would be in wingboards. Wingboards don't really plane without foiling (if you think they do, please send me a video), and even though they could benefit from the second point above (being able to pivot backwards), they can only do this once on plane, because the advantage to being able to pivot here is that there isn't water under the back of the hull.

The "ollie" idea implies this is like the kicktail on a skateboard, which only works because there's empty space underneath it. I don't see how it works if the board isn't operating in a position where the whole bottom is still in the water, and I'm not sure such a position exists on a wingfoil board where the foil isn't already working.
StellaBlu wrote:
Mon Nov 15, 2021 7:02 pm
The other factor is that some tail kick designs create dirty flow and drag, further reducing speed, while a clean cutoff on the tail minimizes that drag.
This is well-established in boat design. You want a clean separation of water off the transom for less drag. A step in the middle of the hull is only fast when the front half of the hull is in the water but the back half is not.

Thanks. I'm not sure I understand your position on this though - are you agreeing that the cut outs don't work as intended and a relatively flat hull is advantageous ? Sorry for being so thick.

I have never been able to get onto the foil from a stand-still. I need to get some speed in the board first before I try pumping it out of the water. This has led to me to believe that shapes that maximize acceleration are the easiest to get up on. I'm not sure what the definition of planing is - but I think speed should take precedence and any cut-out that comes at the expense of acceleration is counterproductive.

We didn't address bottom hull contours - like double concave. I have heard that in flat water, a double concave hull slows acceleration but is advantageous in choppy water. Fanatic 2021 wing boards had double concave hulls but are now completely flat in 2022, arguing that they are quicker to foil now. F-one wing boards don't have aggressive cut outs and are pretty flat , but they are one of the quickest boards I've tried to get up on foil. On the other hand, the axis froth board is smooth and relatively flat but I found it is difficult to get to release from the surface of the water.

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Re: cutouts wingfoil boards

Postby tkaraszewski » Mon Apr 11, 2022 6:28 pm

consumer wrote:
Mon Apr 11, 2022 4:29 pm
tkaraszewski wrote:
Mon Apr 11, 2022 4:00 pm
The traditional reason for steps like this in planing boats or aircraft floats is that while the flotation of the entire hull is required at low speed, once you reach planing speeds, you no longer need so much hull in the water. As the hull rises up onto the forward part, the back of the hull is now up and out of the water, greatly reducing drag. In airplanes, this allows the whole plane to rotate upward by "pivoting" on the step as well, which is great for takeoff.

I'm skeptical of how useful this would be in wingboards. Wingboards don't really plane without foiling (if you think they do, please send me a video), and even though they could benefit from the second point above (being able to pivot backwards), they can only do this once on plane, because the advantage to being able to pivot here is that there isn't water under the back of the hull.

The "ollie" idea implies this is like the kicktail on a skateboard, which only works because there's empty space underneath it. I don't see how it works if the board isn't operating in a position where the whole bottom is still in the water, and I'm not sure such a position exists on a wingfoil board where the foil isn't already working.
StellaBlu wrote:
Mon Nov 15, 2021 7:02 pm
The other factor is that some tail kick designs create dirty flow and drag, further reducing speed, while a clean cutoff on the tail minimizes that drag.
This is well-established in boat design. You want a clean separation of water off the transom for less drag. A step in the middle of the hull is only fast when the front half of the hull is in the water but the back half is not.

Thanks. I'm not sure I understand your position on this though - are you agreeing that the cut outs don't work as intended and a relatively flat hull is advantageous ? Sorry for being so thick.
Yes, mostly, at least in the context of wingfoil boards. The design is all about getting part of the board/boat/plane/etc out of the water so that drag is minimized, but I don't see that happening with wingfoil boards.
consumer wrote:
Mon Apr 11, 2022 4:29 pm
I have never been able to get onto the foil from a stand-still. I need to get some speed in the board first before I try pumping it out of the water. This has led to me to believe that shapes that maximize acceleration are the easiest to get up on. I'm not sure what the definition of planing is - but I think speed should take precedence and any cut-out that comes at the expense of acceleration is counterproductive.
Planing is when the board/boat is being help up not by it's buoyancy but by the high speed water deflecting off the bottom. If you consider a typical performance surfboard, it is not buoyant enough to float its rider. If a surfer attempts to stand on such a board when it is not moving, he will sink up to his waist in the water. Clearly the board cannot float him. But when the surfer is riding a wave, he stands on the board on top of the water. Why does the board hold him up now? Because it is planing, and the force of the water pushing at high speed against the bottom of the board holds it up on top of the water. If it slows down too much, it will begin to sink. This is planing.

Being able to plane or not is dependent upon the speed you can reach, not your acceleration. Let's say a particular boat needs to go 12 knots to plane. It does not matter if it takes 10 minutes for it to go from 0-12 knots, it will eventually cross over that speed threshold and come up onto a plane on top of the water.

On the other hand, say the boat accelerates very quickly, but only to a top speed of 10 knots. It can do 0-10 in 3 seconds flat. This doesn't help it plane at all, because it never reaches 12 knots. It's not the acceleration tat gets it on plane, it's the speed.

The same is true of foils, BTW. Because foils are just underwater wings, they also have a stall speed, and like a 747 that needs to reach ~150 knots to take off, it doesn't really matter how long it takes the plane to get up to that speed, so long as it eventually does. Once it gets above it's stall speed, it can start to fly, even if it takes several minutes. Your foil does the same. You don't need acceleration to foil, you need speed.

My contention is that the point of a hull cutout is not to assist in getting onto plane, it's to reduce drag while on plane, allowing for even more acceleration up to a higher speed - which is why they're so useful on floatplanes. However, if you can never reach a planing speed at all, the cutout does not help, and in fact hurts, because a flat bottom has less drag than one with a step in the middle of it.

I think that for most wingfoil boards, planing speed is higher than foiling speed, so you will come up on foil before any planing speed advantages actually take effect. Like I said, if anyone has a video of a wingfoil board planing on the front half of the board with the stepped tail out of the water, I'd love to see it.
consumer wrote:
Mon Apr 11, 2022 4:29 pm
We didn't address bottom hull contours - like double concave. I have heard that in flat water, a double concave hull slows acceleration but is advantageous in choppy water. Fanatic 2021 wing boards had double concave hulls but are now completely flat in 2022, arguing that they are quicker to foil now. F-one wing boards don't have aggressive cut outs and are pretty flat , but they are one of the quickest boards I've tried to get up on foil. On the other hand, the axis froth board is smooth and relatively flat but I found it is difficult to get to release from the surface of the water.
I think deep concaves do more to improve tracking and wave interaction than they do to improve speed. Ultimately, since the shortest distance between two points is a straight line, a flat bottom has less surface area and thus less drag than a curved bottom.

Ultimately, my own view is that it's all sort of gimmicky. Like you've seen, different manufacturers and even the same manufacturers from year to year have "drastically changed" their boards with or without these features, but put two skilled riders on similar sized boards with similar foils and wings and you'll see similar results. You are not going to see top guys going out in 12 knots on a flat board but being able to start in 9 knots on a step-tailed board in otherwise similar conditions, nor vice-versa. In light conditions, a short gust with 2-3 more knots of wind will make a lot more difference than bottom shape differences in the board.
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