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Do all carbon mast do this?

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consumer
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Re: Do all carbon mast do this?

Postby consumer » Mon Jul 18, 2022 3:41 am

Any stiffness should have the propensity to wobble. It’s how the wobble is dampened. I’m not sure if this is considered when fiber orientation and the attached components are designed.

Have you thought about placing one of those rubber shims between the board and mast plate? Maybe it will help absorb vibrations like this

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Re: Do all carbon mast do this?

Postby drone » Mon Jul 18, 2022 6:50 am

consumer wrote:
Mon Jul 18, 2022 3:41 am
Any stiffness should have the propensity to wobble. It’s how the wobble is dampened. I’m not sure if this is considered when fiber orientation and the attached components are designed.

Have you thought about placing one of those rubber shims between the board and mast plate? Maybe it will help absorb vibrations like this
I have already rubber shim, does not help. Its wobble at lower half, base and upper half are really thick.
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Re: Do all carbon mast do this?

Postby downunder » Mon Jul 18, 2022 10:28 am

Actually Moses does this as well.

The longer the mast, more wobble that is. Not sure how does affect racers, but then they race on >3000 Euros gear.
Like MikeLab foils etc.

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Re: Do all carbon mast do this?

Postby Windigo1 » Mon Jul 18, 2022 1:10 pm

drone wrote:
Sat Jul 16, 2022 4:58 pm
Turbaani wrote:
Sat Jul 16, 2022 1:57 pm
What mast is that drone?

Sabfoil masts seem very solid. I thought they copied it for SS but apparently not. I've seen some very flexy windfoil masts too, sabfoil windfoil mast is rock solid.
Slingshot Phantasm 92cm.
Wow very disappointing that was supposed to be one of the big selling point of the Phantasm the super stiff new mast.

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Re: Do all carbon mast do this?

Postby consumer » Mon Jul 18, 2022 2:53 pm

drone wrote:
Mon Jul 18, 2022 6:50 am
consumer wrote:
Mon Jul 18, 2022 3:41 am
Any stiffness should have the propensity to wobble. It’s how the wobble is dampened. I’m not sure if this is considered when fiber orientation and the attached components are designed.

Have you thought about placing one of those rubber shims between the board and mast plate? Maybe it will help absorb vibrations like this
I have already rubber shim, does not help. Its wobble at lower half, base and upper half are really thick.
Darn. I share your frustration dude.

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Re: Do all carbon mast do this?

Postby PugetSoundKiter » Mon Jul 18, 2022 6:57 pm

Is this input (impulse of this force on one wingtip only perpendicular to the plane of the wing) common when riding the foil?

Is the dampening of the foil upside down in the air only under it’s own weight similar to the dampening of this harmonic frequency the foil would get when ridden thru water under load?

If a different wing, fuselage or stabilizer was used then the torsional vibration frequency would change and a different tuned dampener might be needed? But If it rides fine and this is a byproduct of stiff and light, then why the concern over this unrelated antic?

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Re: Do all carbon mast do this?

Postby spiru » Mon Jul 18, 2022 7:48 pm

I have just got a 102 Phantasm mast and love it. I have put in almost 500km in 4 days and rides perfectly at all angles and speeds, both in flat and choppy water. After years suffering spontaneous ventilations with aluminum masts (Liquid Force Gong V1 and GongV2) the phantasm masts gives me the confidence to go all in knowing that is going to hold well.
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Re: Do all carbon mast do this?

Postby tkaraszewski » Mon Jul 18, 2022 8:24 pm

I did the same test on my Levitaz R5:

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Re: Do all carbon mast do this?

Postby Nelis » Tue Jul 19, 2022 9:47 am

I'm quite sure my 2019-ish gen Levitaz 96cm does a lot worse than that R5. And I upgraded from a 2017 model for more stiffness. Maybe I'll post a vid as well.

Honestly I think there is truth in PugetSoundKiter's comments. This torsional load case is probably the worst 'looking' you can do for a foil mast, especially since they are designed to be stiff in other directions and hydrodynamic requirements are top priority. Aside from very small winglets, there are no real acting planes resisting this load case anyways.

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Re: Do all carbon mast do this?

Postby BayAreaKite » Tue Jul 19, 2022 5:20 pm

This is called resonant frequency (in the torsional mode). Resonant frequency is sqrt(k/m) with k=stiffness and m=mass. Therefore, two masts with the same stiffness can actually have different resonant frequencies (wobble) if the mounted wings are different weights. While this test can be insightful into stiffness, it is more accurate to twist the mast statically to remove any effects of wing weight or fuselage length. To do this, twist the mast with a known force and record deflection. This will tell you the stiffness of the mast by eliminating other variables that affect dynamic test results.

When the mast is in the water, it is effectively damped. Damping is not the same as stiffness. A carbon mast with the same stiffness as an aluminum mast will have better damping characteristics due to the intrinsic properties of the composite material. You might feel this in the water with less vibration, but it's still the same stiffness as the aluminum mast. It also may wobble more or less in this test, but again both masts have the same stiffness. In the case of Project Cedrus, the rubber edges actually add additional damping to further reduce vibration.

Torsional stiffness is critical when yawing the wings. For example, tight turns in the surf, a quick upwind tack. The input comes from the rider/board, not the wing[tips] or vertical stabilizer if applicable. Inertia and drag prevent wings from yawing, so a stiffer mast helps. Furthermore, it can reduce the likelihood of ventilation by reducing the amount of twist in the mast at aggressive angles of attack. A twisting mast can cause flow separation/stalling. Ventilation is very complex, and torsional stiffness is only one of the factors.

Oddly the new Axis HM carbon mast has lower torsional stiffness than their aluminum mast. Devon with Wake Thief did a really good test of it, with proper loadcases (not just hanging weight of the end of the mast). https://www.youtube.com/watch?v=EV6O5vQep8Y From a technical standpoint, there's really no excuse for a carbon mast have lower torsional or bending stiffness than an aluminum mast. Carbon is much stiffer than aluminum, so when properly engineered it should be superior from every standpoint. I wrote about this here: https://projectcedrus.com/general/solid ... sites-101/

It's nice to see the industry recognizing the importance of stiffness. However proper testing and engineering is critical to maximizing it, and based on how some brands continue to test their masts, they will be lead down the wrong path of design...
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