Contact   Imprint   Advertising   Guidelines

Foil sanding to get rid of turbulence

A forum dedicated to Hydrofoil riders
Cefirmeza
Medium Poster
Posts: 146
Joined: Fri Aug 14, 2015 8:30 pm
Kiting since: 2014
Weight: 65kg
Local Beach: Ceará - Brazil
Favorite Beaches: Ceará, Brazil
Style: Kitefoil Wingfoil
Gear: Slingshot sst 4m, Airush Ultra 5m, brm cloud 5.5m, Peak4 4m/6m, Duotone Slick 3.5/4.5m
Sabfoil W1000,W800, Lift classic 150
Armstrong SKT3’11 25L
Brand Affiliation: None
Has thanked: 35 times
Been thanked: 10 times
Contact:

Foil sanding to get rid of turbulence

Postby Cefirmeza » Wed Jun 01, 2022 10:31 pm

I am experiencing turbulence and draggy noise when riding at low speeds. Already sanded both mast and back wing trailing edges both sides at 30 degrees and still there. I did more than 20 pre session sanding and now it is quite sharp. What would happen if I sand them square tips at 90 degrees?

rnelias
Very Frequent Poster
Posts: 1133
Joined: Mon Sep 16, 2019 11:07 pm
Local Beach: RJ, Brazil
Favorite Beaches: Arubinha, RJ
Cumbuco, CE
Barra da Tijuca, RJ
Praia da Bica, RJ
Style: freeride
Gear: Boxer 9m for foiling
Rebel SLS 8m or Crave HL 9m for boosting on twintip
Brand Affiliation: None
Has thanked: 290 times
Been thanked: 269 times

Re: Foil sanding to get rid of turbulence

Postby rnelias » Thu Jun 02, 2022 1:50 pm

Cefirmeza wrote:
Wed Jun 01, 2022 10:31 pm
I am experiencing turbulence and draggy noise when riding at low speeds. Already sanded both mast and back wing trailing edges both sides at 30 degrees and still there. I did more than 20 pre session sanding and now it is quite sharp. What would happen if I sand them square tips at 90 degrees?
Are you sure it's due to trailing edge finish? I mean, draggy noise/behavior, like foil scraping the water instead of cutting, could also be due to surface imperfections. Bubbles adhere at the surface. At higher speeds these bubbles can implode and affect the wing's lift (ventilation effect). However, if the foil is whistling, it's usually due to the trailing edge finish. Here's a picture that I've got from this post https://windfoilzone.com/why-is-my-hydrofoil-whistling/ that shows the vibration amplitude according to the trailing edge finish.
a4ab0b_599a31cada8f4b81970f47496a975695_mv2_d_1724_1588_s_2.png
from this picture, the worst case scenario would be sanding it at 90 degrees :cry:
Last edited by rnelias on Fri Jun 03, 2022 2:46 am, edited 1 time in total.

User avatar
darippah
Very Frequent Poster
Posts: 627
Joined: Sun Apr 22, 2012 9:07 pm
Kiting since: 2011
Weight: 165
Local Beach: New Jersey, USA
Style: Hydrofoil big air
Gear: Sonic 3 13m , Soul 7 and 10m
Brand Affiliation: None
Has thanked: 7 times
Been thanked: 24 times

Re: Foil sanding to get rid of turbulence

Postby darippah » Fri Jun 03, 2022 1:25 am

rnelias wrote:
Thu Jun 02, 2022 1:50 pm
Cefirmeza wrote:
Wed Jun 01, 2022 10:31 pm
I am experiencing turbulence and draggy noise when riding at low speeds. Already sanded both mast and back wing trailing edges both sides at 30 degrees and still there. I did more than 20 pre session sanding and now it is quite sharp. What would happen if I sand them square tips at 90 degrees?
Are you sure it's due to leading edge finish? I mean, draggy noise/behavior, like foil scraping the water instead of cutting, could also be due to surface imperfections. Bubbles adhere at the surface. At higher speeds these bubbles can implode and affect the wing's lift (ventilation effect). However, if the foil is whistling, it's usually due to the leading edge finish. Here's a picture that I've got from this post https://windfoilzone.com/why-is-my-hydrofoil-whistling/ that shows the vibration amplitude according to the leading edge finish.

a4ab0b_599a31cada8f4b81970f47496a975695_mv2_d_1724_1588_s_2.png

from this picture, the worst case scenario would be sanding it at 90 degrees :cry:
You mean TRAILING EDGE !!! :cool2:
These users thanked the author darippah for the post:
rnelias (Fri Jun 03, 2022 2:46 am)
Rating: 3.03%

rnelias
Very Frequent Poster
Posts: 1133
Joined: Mon Sep 16, 2019 11:07 pm
Local Beach: RJ, Brazil
Favorite Beaches: Arubinha, RJ
Cumbuco, CE
Barra da Tijuca, RJ
Praia da Bica, RJ
Style: freeride
Gear: Boxer 9m for foiling
Rebel SLS 8m or Crave HL 9m for boosting on twintip
Brand Affiliation: None
Has thanked: 290 times
Been thanked: 269 times

Re: Foil sanding to get rid of turbulence

Postby rnelias » Fri Jun 03, 2022 2:47 am

darippah wrote:
Fri Jun 03, 2022 1:25 am
You mean TRAILING EDGE !!! :cool2:
fixed, thx :wink:

ieism
Frequent Poster
Posts: 311
Joined: Sun Jun 21, 2020 8:56 pm
Kiting since: 2019
Local Beach: Ijmuiden
Favorite Beaches: Beauduc, Rockanje
Style: Foil.
Gear: Flysurfer Peak 5: 4/5/6/8/11m
Kauper XT Falcon 11m
Dwarfcraft 110cm
Gong Curve, Pro stab fuse 85 carbon mast
Brand Affiliation: None
Location: Amsterdam
Has thanked: 89 times
Been thanked: 94 times

Re: Foil sanding to get rid of turbulence

Postby ieism » Fri Jun 03, 2022 7:15 am

I'm not convinced it's always the trailing edge. I sanded mine and fixed some scratches and the foil was silent. Then after using it a lot it went back to whistling again. But now I mounted it on a different board and it's silent again. I have no idea why.

Matty V
Very Frequent Poster
Posts: 631
Joined: Mon Mar 23, 2020 2:24 pm
Kiting since: 1998
Gear: Home made
Brand Affiliation: None
Has thanked: 44 times
Been thanked: 119 times

Re: Foil sanding to get rid of turbulence

Postby Matty V » Fri Jun 03, 2022 9:18 am

99.9% of the time where surface finish is concerned you will make it worse.

Also if it’s a standard recreational alloy/glass”carbon” foil there are bigger issues likely causing the issues that aren’t the TE

Like for terrible fit between mast and fuselage, screws sticking out, the awkward joint between rear wing and fuselage or front wing and fuselage the crappy moulding slightly oversized and out of shape all of those will be causing for bigger issues with your foil

It’s also a case of what you actually trying to do sand it to make it faster or sand it to make it quieter because those two things are not always exclusive, You could end up with a nice quiet foil to actually go slower and stalls more easily after you’ve butchered the trading age or smooth window party all over it to try and flatten the surface when actually really didn’t need it

So before you pick up the sandpaper really think what you’re trying to do before you go in the trash actually works pretty darn well in the first place

If it’s for a full race for this is literally the worst place you could be asking for advice go to the people that made it
These users thanked the author Matty V for the post:
rnelias (Sat Jun 04, 2022 3:06 pm)
Rating: 3.03%

User avatar
Peter_Frank
Very Frequent Poster
Posts: 12710
Joined: Wed Oct 16, 2002 1:00 am
Brand Affiliation: None
Location: Denmark
Has thanked: 993 times
Been thanked: 1177 times

Re: Foil sanding to get rid of turbulence

Postby Peter_Frank » Fri Jun 03, 2022 7:44 pm

I am a bit uncertain about what you experience?

You say at slow speeds, turbulence and draggy noise?

Is it the high pitch noise, or is it low pitch subtle humming?

Usually the TE shape will give the high pitch noise, louder and more screaming the faster you go.

At low speeds, if your wing is really low aspect, it will feel like a deep sound - even if it can not be heard but felt.

I remember this clearly, the first time many years ago when I got my first low aspect wave wing.

When I was carving at low speeds, I thought something was wrong, and I felt a noise from turbulence, so clear that I could have sworn I could hear a sound - although probably not..

But this was simply because such a wing can be ridden at ridiculously high AOA without stalling.
And as my body was not tuned in for this wing, I rode it just a tad too high angle of attack, without stalling - which can deliver severe vibrations.

It went away over time when I got used to this wing - had nothing to do with sanding.

Probably no the case here, and you might know all this - but would still give my input and share this.

8) Peter

Trent hink
Very Frequent Poster
Posts: 986
Joined: Mon Jan 07, 2019 4:59 am
Kiting since: 1998
Weight: 83 kg.
Local Beach: Nokomis beach, Turtle beach, Venice inlet, lido key
Style: Creepy old man
Gear: Peak4, LF, solo, Moses 633 hydrofoil, couple of surfboards, a twintip I made in 2008.
Brand Affiliation: once made an attempt to manufacture and market "Anomaly" twin-tip boards.
Has thanked: 291 times
Been thanked: 248 times

Re: Foil sanding to get rid of turbulence

Postby Trent hink » Fri Jun 03, 2022 9:28 pm

I'm not the sharpest crayon in the box, but based on my interpretation of the chart you posted, it seems like #2 and #3 are the worst case scenarios?

When I built the rudder for my outrigger sailing canoe, the information I gathered (from boat building forums) suggested that sanding the trailing edge down square to about 1-3 mm wide was the best way to go.

Granted, most sailboats go much slower than most hydrofoils,
and usually the tolerances are not nearly as close, so for sure it is not quite the same thing....

rnelias wrote:
Thu Jun 02, 2022 1:50 pm
Cefirmeza wrote:
Wed Jun 01, 2022 10:31 pm
I am experiencing turbulence and draggy noise when riding at low speeds. Already sanded both mast and back wing trailing edges both sides at 30 degrees and still there. I did more than 20 pre session sanding and now it is quite sharp. What would happen if I sand them square tips at 90 degrees?
Are you sure it's due to trailing edge finish? I mean, draggy noise/behavior, like foil scraping the water instead of cutting, could also be due to surface imperfections. Bubbles adhere at the surface. At higher speeds these bubbles can implode and affect the wing's lift (ventilation effect). However, if the foil is whistling, it's usually due to the trailing edge finish. Here's a picture that I've got from this post https://windfoilzone.com/why-is-my-hydrofoil-whistling/ that shows the vibration amplitude according to the trailing edge finish.

a4ab0b_599a31cada8f4b81970f47496a975695_mv2_d_1724_1588_s_2.png

from this picture, the worst case scenario would be sanding it at 90 degrees :cry:

rnelias
Very Frequent Poster
Posts: 1133
Joined: Mon Sep 16, 2019 11:07 pm
Local Beach: RJ, Brazil
Favorite Beaches: Arubinha, RJ
Cumbuco, CE
Barra da Tijuca, RJ
Praia da Bica, RJ
Style: freeride
Gear: Boxer 9m for foiling
Rebel SLS 8m or Crave HL 9m for boosting on twintip
Brand Affiliation: None
Has thanked: 290 times
Been thanked: 269 times

Re: Foil sanding to get rid of turbulence

Postby rnelias » Sat Jun 04, 2022 3:02 pm

Trent hink wrote:
Fri Jun 03, 2022 9:28 pm
I'm not the sharpest crayon in the box, but based on my interpretation of the chart you posted, it seems like #2 and #3 are the worst case scenarios?

When I built the rudder for my outrigger sailing canoe, the information I gathered (from boat building forums) suggested that sanding the trailing edge down square to about 1-3 mm wide was the best way to go.

Granted, most sailboats go much slower than most hydrofoils,
and usually the tolerances are not nearly as close, so for sure it is not quite the same thing....
Yep... these configurations would give higher vibration amplitude (noise usually comes from short and high frequency vibrations though). This diagram came from “Principles of Yacht Design” book by Lars Larsson and Rolf E. Eliasson. There's a session devoted to Keel and rudder design. I have this book and the paragraph regarding this Figure is bellow:

Fig 6.35 shows some alternatives. An interesting phenomenon is the vibration that
occurs for certain shapes. The figure shows the amplitude of the vibrations at resonance
for each case relative to those of a square cut-off. It can be seen that if the edge is
symmetric and wedge-shaped (cases 2–5), the total wedge angle has to be 30° or smaller.
For 90° and 60° much larger vibrations occur than for the square ending. This is also the
case if the ending is rounded in some way, which it normally is, if the trailing edge of
the keel or rudder is left without attention. An asymmetric cut-off is somewhat more
forgiving, and a 45° cut-off is acceptable, provided the corner on the cut-off side is
smoothed. The vibrations are not only of academic interest. On the contrary, they may
cause severe vibrations and noise in the entire hull at speeds where resonance occurs.
Using the information in Fig 6.35 these problems can be solved.

Matty V
Very Frequent Poster
Posts: 631
Joined: Mon Mar 23, 2020 2:24 pm
Kiting since: 1998
Gear: Home made
Brand Affiliation: None
Has thanked: 44 times
Been thanked: 119 times

Re: Foil sanding to get rid of turbulence

Postby Matty V » Sat Jun 04, 2022 4:05 pm

Yacht rudder and keel design.. brilliant

This is why the internet is stupid. A normal yacht with a keel operates in a 6-12 kt speed range.

Our kite foils are a magnitude thinner in profile and operate at speeds 3-4 times that of the article.

Think before you sand


Return to “Hydrofoil”

Who is online

Users browsing this forum: Brent NKB, Peter_Frank and 59 guests