Forums > Windsurfing Foiling

Where is the whistle coming from and what do you think about it?

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Created by MProject04 > 9 months ago, 17 Sep 2020
MProject04
442 posts
17 Sep 2020 2:47PM
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This has probably been mentioned in the forum but could not find a dedicated thread.

1) Where is the (damn!) whistling coming from when foiling? Is it really from the foil? The mast? Or is it the sail?
2) What do you think about it? Does it make you happy or do you hate it? Do you find it embarrassing?
3) What can one do about it? I read something about sanding. Is that good or bad?

Keen to hear opinions!

Windbot
471 posts
17 Sep 2020 3:17PM
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Have you seen this?

AUS154 Chris
QLD, 217 posts
17 Sep 2020 5:22PM
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It's the mast. I have silenced it by agressively reshaping the trailing edge so it's not so blunt.

Smidgeuk
70 posts
17 Sep 2020 5:21PM
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Sails can whistle too. I have one that when set in a particular way will whistle in a similar way to my old NP pink foil mast. The way to know which is which is that the foil mast will whistle consistently when you hit a certain speed (quite fast on the NP pink one), whereas if you try different sails and it goes away, or with the same sail and sometimes its there and sometimes not depending on how you set it, then its the sail. I dont like it, others like it as it creates more impression of speed.

MProject04
442 posts
17 Sep 2020 5:42PM
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Windbot said..
Have you seen this?



Is this possible for carbon mast too?

CoreAS
869 posts
17 Sep 2020 9:43PM
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On the NP pinkie it was the trailing edge of the mast as the mold left it slightly rounded.

On the 2018/19 Naish It was the trailing edge of the front wing that needed sanding (very carefully) that thing wasn't a whistle it was a fog horn.

Slingshot foils the only noise you hear is your teeth from smiling

azymuth
WA, 1962 posts
17 Sep 2020 9:48PM
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CoreAS said..
Slingshot foils the only noise you hear is your teeth from smiling


Very nice

PatK
295 posts
17 Sep 2020 9:49PM
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Its the mast. And i hate it! I also hate the damn whistling of some slalom fins.
The NP pinkie did it and my sb race foil carbon mast did it too. The Severne redwing also a bit.
If sanding fixes it, why do they not do it before anodizing? Sandpaper kills the coating!

By the way, my Moses Vento 790 with carbon mast is absolutely total silent. No whistle and no wobble

DB2
98 posts
17 Sep 2020 9:54PM
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My Moses 790 whistles like crazy, so you never know what you get until you try it.

dejavu
807 posts
17 Sep 2020 9:57PM
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The Moses 75 cm. aluminium mast I demoed whistled -- I was sent a diagram of where to sand. The manufacture should fix these issues not the end user (customer). No problem with my Sling Shot masts and foils.

PatK
295 posts
17 Sep 2020 10:01PM
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The moses 790 of my mate is silent too. That was one of the reasons why i bought it.

The only issue i have with it is the front screw of the mast/fuse connection is self opening while foiling. So i always take the wrench with me on the water.

IndecentExposur
297 posts
18 Sep 2020 12:12AM
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sharper trailing edge of your foils. My sails don't whistle, but they will buzz from time to time.

robbo1111
NSW, 620 posts
18 Sep 2020 7:59AM
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There's a video on the Gofoil site showing how to stop whistling. It's usually caused by the stabiliser according to Alex Aguera. I did what he suggested and it worked

oscardog
208 posts
18 Sep 2020 7:28AM
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CoreAS said..

Slingshot foils the only noise you hear is your teeth from smiling



I managed to get a whistle from a Slingshot set up, but was going so fast vs normal (the wind was excellent) that my smiling teeth drowned out the whistle noise. Slingshot whistle was quieter than NP pinkie.

Now I crave the whistle.

Ian K
WA, 4039 posts
18 Sep 2020 10:26AM
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Is it vortex shedding harmonising with the natural vibration frequency of the foil arm? In which case does the frequency and speed needed vary on the 75 cm pinkie vs the 90cm pinkie? You'd reckon the amount of foil arm in the water would affect the damping and frequency? It seems to be more inclined to hum going off the wind where side loading is less.

I like the hum. Was running out of things to think about after decades of sailing slappers.

Gorgo
VIC, 4911 posts
18 Sep 2020 1:31PM
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There are many reasons why foils whistle and they're not all the same.

I've had whistling from pin holes in the carbon around the leading edge, a tiny split in the leading edge, and the shape of the trailing edge as per the GoFoil example.

Over the years I've done a fair bit of sanding and filling the edges of my foils and did the GoFoil thing on my GoFoils. Everything worked more or less.

Usually the foil is silent after the maintenance treatment, then sound builds up over 50-100 hours.

I recently re-constructed the tip of my favourite foil (mainly as a lockdown project and to build my carbon/epoxy/vacuum skills). The finished foil has a velvety smooth ride and has a slight rumbling sound at high speed. It sounds like a jet engine running up to take off. I love it.

I have zero sharp edges on any of my foils. They're certainly not necessary for any freeride gear. I've never been cut by a foil. The racers go a fair bit faster than me, and on higher angles, but nobody else does.

segler
WA, 1597 posts
19 Sep 2020 12:11AM
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Yes, exactly that: "Is it vortex shedding harmonising with the natural vibration frequency of the foil arm?"

For the AFS-2 the whistling was in the trailing edge of the stab. Bruce Peterson and I (and some of his other customers) messed around with changing the shape of the trailing edge to reduce the whistle (in my case it was a howl). We never completely eliminated it. I think there is a natural harmonic in the stab structure that is resonating with the shedding frequency.

This vortex shedding issue is very well known in the hydro power industry, where they had to tweak the trailing edges of turbine blades. If those blades whistle, they fail quickly.

Some foils are noisy, some are quiet. Some people have brown eyes, some blue.

Pacey
WA, 525 posts
19 Sep 2020 2:49PM
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IndecentExposur said..
sharper trailing edge of your foils. My sails don't whistle, but they will buzz from time to time.


Don't sharpen your trailing edges, that's just stupid.

The problem is probably that your trailing is a bit rounded. Solution is to square it off with 600 grit and a block so the trailing edge is about 0.5 mm wide. If you still get vibration or whistling after that then angle the squared off trailing edge by about 10-20 degrees.

azymuth
WA, 1962 posts
19 Sep 2020 7:38PM
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Pacey said..

IndecentExposur said..
sharper trailing edge of your foils. My sails don't whistle, but they will buzz from time to time.



Don't sharpen your trailing edges, that's just stupid.

The problem is probably that your trailing is a bit rounded. Solution is to square it off with 600 grit and a block so the trailing edge is about 0.5 mm wide. If you still get vibration or whistling after that then angle the squared off trailing edge by about 10-20 degrees.


Andrew - how far can you go with squaring it off before the anodising layer is destroyed?

Pacey
WA, 525 posts
19 Sep 2020 8:49PM
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azymuth said..


Pacey said..



IndecentExposur said..
sharper trailing edge of your foils. My sails don't whistle, but they will buzz from time to time.





Don't sharpen your trailing edges, that's just stupid.

The problem is probably that your trailing is a bit rounded. Solution is to square it off with 600 grit and a block so the trailing edge is about 0.5 mm wide. If you still get vibration or whistling after that then angle the squared off trailing edge by about 10-20 degrees.




Andrew - how far can you go with squaring it off before the anodising layer is destroyed?



Very little, it's pretty thin. The black colour is just a dye that soaks into the oxide layer, so if its not black anymore, your anodising is likely to be gone.
Although I occasionally sand my Slingshot foils with 600 grit, I don't sand the anodised aluminium bits. Fortunately they don't whistle

segler
WA, 1597 posts
20 Sep 2020 12:18AM
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The Laboratory for Hydraulic Machines says do not square the trailing edge. They wrote a paper about this for the hydro power industry. This is what Sailwors uses to reduce the whistle on AFS stabs. I can't attach it since it is a pdf file, so I will try a plain text paste here. Problem is that the paste omits the tables and drawings. However, I attached one of the drawings. #10 was the best design.

Chapter 1. Problem
overview
11
-Concepts of fluid-dynamic attenuation/control of vortex shedding
The control of the vortex shedding to reduce the vibration is presented through the following
methods:
a)Trailing edge geometry modification
Trailing edge geometry modification in the case of the elongated bodies such as vanes, blades,
and plates reduces vortex-induced excitation considerably. The effect of the trail- ing edge shape
on the vortex-induced vibration of plates has been investigated by different authors such as
Donaldson [17], Heskestad [37], Toebes [72] and Blake [13]. The summary of these studies is
illustrated in the Table 1.1.
Table 1.1: Trailing edge shapes investigated and their relative amplitude of vibration, Blake
[13]
Donaldson [17] performed systematic measurements of flow-induced vibration in Francisturbine
runners having different trailing edge shapes, Figure 1.8.
It was found that none of the trailing edge shape modifications changed the frequency of the
exciting forces. The vibration amplitude of different trailing edges versus velocity and also the
percentage amplitude in relation to the blunt trailing edge is presented in
EPFL - Laboratory for Hydraulic Machines
FAULTY TRANSITION PIECES
PREVIOUS HAND SANDING
NEW CNC CLIPPING JOB
12 I.
Introduction
Figure 1.8: Trailing edge shape, Donaldson [17]
Figure 1.9. Minimum vibration in comparison to the blunt trailing edge was found for the
trailing edge numbers 8, 9, 10.
The vortex shedding from a cambered hydrofoil with beveled trailing edge with angles of 44?
and 56? at high Reynolds number was studied by Dwayne [21]. He noted that the turbulent
fluctuations in the near wake depend on the Reynolds number due to the Re- dependence of
separating boundary layers on both sides of the hydrofoil, interacting to form the near wake. In
addition, the trailing edge geometry has an effect on the relative strength of the vortex shedding.
The ticker or blunter trailing edge produces stronger vortex shedding. Moreover, the
boundary layer is separated at the beveled side of the trailing edge and asymmetric vortex
shedding is found. Mosallem [52] investigated the characteristics of the flow past beveled
trailing edges attached to the flat plates with angles of 27? and 60?. The results display an
asymmetric wake behind the 27? beveled trailing edge contrary to the 60?case where a symmetric
wake is observed. Greenway [29] studied the effect of beveled trailing edge on vortex shedding
and vibration using a wind tunnel. It was found that the beveled trailing edge suppressed the vortex
excited vibration due to the rapid decay of the vortex resulting from an asymmetric circulation
distribution in the vortex formation region. He performed the measurement for different trailing
edge angles between 20? and 90?. As the trailing edge angle decreases, the vortex strength
becomes smaller. In addition, the vortices shed from the suction side are stronger than those from
the pressure side.
EPFL - Laboratory for Hydraulic
Machines
OPTIMUM TRAILING EDGE
The main challenge is that 1.8T
shall correspond to an approximate
value of <2mm
Chapter 1. Problem
overview
13
Figure 1.9: Vibration amplitude of various trailing edge shapes, Donaldson [17]
In the domain of hydraulic machine, fatigue cracks in stay vanes have occurred in
several hydro power stations over the years, [33], [48], and [27]. Two basic principles are
known to solve the problem, Grein [30]. The first is to modify the trailing edge to reduce the
vibration excitation and the second is to alter the natural frequency of the stay vanes. A
comprehensive review of stay vane cracking in hydraulic turbine has been presented by Gummer
[33]. The stay vane failure in the NKula Falls hydro power plant was resolved by modification
of trailing edge as reported by Fisher [24]. Lockey [49] noted the vortex-induced vibration
reduction in Ontario power generation by modifying the original trailing edge of stay vane to a Vshaped
trailing edge. The same modification was also reported for Little Long Generation station
north of Toronto by Goldwag [27].
EPFL - Laboratory for Hydraulic
Machines





airsail
QLD, 1239 posts
20 Sep 2020 8:19AM
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An explanation from Levitaz, not sharp, not square and which surface to sand.

stehsegler
WA, 3450 posts
20 Sep 2020 8:04AM
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Really begs the question why these brands sell $3,000 foil setups that then need to have the edges sanded by the end customers.

excav8ter
536 posts
20 Sep 2020 8:52AM
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A friend of mine wing foils with a GoFoil setup, when we're really cruising along, I can hear him from over 100 yards away.... easily. He, however, cannot hear me on my Levitator 160 my SS setup as I come up on him and pass him.

MProject04
442 posts
21 Sep 2020 2:50AM
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stehsegler said..
Really begs the question why these brands sell $3,000 foil setups that then need to have the edges sanded by the end customers.


indeed! Perhaps their online shop should have an option "would you like us to remove the whistling noise" Y/N?

MProject04
442 posts
21 Sep 2020 2:57AM
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airsail said..
An explanation from Levitaz, not sharp, not square and which surface to sand.


He mentions water temps! Could it be that when water temp is higher, there is more noise?
I've had lots of whistling this summer.. the water was warmer than ever... I was also foiling faster than ever!
Will keep my ears open in coming months as we head into ice cold water!

LeeD
3939 posts
21 Sep 2020 2:58AM
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Humm good?
Scares away fish, seals, and turtles, so you don't skewer them and then get catapulted.
Or at least get their attention.

AUS154 Chris
QLD, 217 posts
21 Sep 2020 7:15AM
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LeeD said..
Humm good?
Scares away fish, seals, and turtles, so you don't skewer them and then get catapulted.
Or at least get their attention.


You may have a point, but you also may have to duck from projectiles thrown by angry yachties.

segler
WA, 1597 posts
22 Sep 2020 12:17AM
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Some racers say they actually like the noise since they can be heard by other racers. Helps prevent collisions on the course.

LeeD
3939 posts
22 Sep 2020 12:23AM
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Not sure what "yaughties" are, but you can bet they are not athletes who can hit anything they try to throw at.
I isolated my loud buzz as rear wing related.

Sandman1221
2776 posts
8 Oct 2020 5:11AM
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My AFS Wind95 had a light whistle just as I was getting up and then it went away. I then noticed the leading wing screw head, and trailing stab screw head, projected a little above the surface on one side of the screw head so I filed them down to make them flush with the wing/stab surface and since then the foil has been perfectly quiet at all speeds in up to 22 knot winds.



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"Where is the whistle coming from and what do you think about it?" started by MProject04