Vibration under Sail just over 4 Knots

Evo18

New member
2
0
Hi All,
Was wondering if Anyone has had a Similar problem to what we are currently having.
We have an 18ft Sport Boat and are getting a serious Hum / Vibration on the Boat under sail.It Starts at around 4 Knots.
Any Idea on what it could be , or how to get rid of it.
Thanks
 

vibroman

Super Anarchist
Resonant vibration on keel and or rudder. Caused by vortexes shedding from training edge exciting natural frequency of foil. Make trailing edge asymmetric by chamfering at 45 degs.

Oh and fuck off newb you need to make the traditional offering.
 

slug zitski

Super Anarchist
7,104
1,469
worldwide
Hi All,
Was wondering if Anyone has had a Similar problem to what we are currently having.
We have an 18ft Sport Boat and are getting a serious Hum / Vibration on the Boat under sail.It Starts at around 4 Knots.
Any Idea on what it could be , or how to get rid of it.
Thanks
Yah

it’s the foils

google it, some simple solutions
 

Evo18

New member
2
0
Resonant vibration on keel and or rudder. Caused by vortexes shedding from training edge exciting natural frequency of foil. Make trailing edge asymmetric by chamfering at 45 degs.

Oh and fuck off newb you need to make the traditional offering.
Thanks Vibroman , i appreciate your reply regarding the issues we are encountering.
 

EYESAILOR

Super Anarchist
3,678
2,135
First of all, Welcome to SA and congratulations on your new boat. Please ignore all requests for the customary offering....that custom died our years ago (thankfully) .

I'm assuming you have bought a VX Evo from your user name.

Mr. Vibro has identified the likely reason and given good advice.
(In passing, he has wisely kept images of the truly lovely Mrs Vibro to himself . I have met her and she is a keeper.)

If you cannot resolve the problem then @VelaSailingSupply , aka Rod Favela is the font of all wisdom about VX Evos
 

nolatom

Super Anarchist
3,690
702
New Orleans
Resonant vibration on keel and or rudder. Caused by vortexes shedding from training edge exciting natural frequency of foil. Make trailing edge asymmetric by chamfering at 45 degs.

Oh and fuck off newb you need to make the traditional offering.

Spell check get you, or not? I'm thinking it's "trailing" edge? And "exiting" natural frequency..?

Or maybe not, English major here.
 

slug zitski

Super Anarchist
7,104
1,469
worldwide
I've only experienced notable hums at and above 10-ish knots, but have never sailed a truly high-performance boat. Does a serious hum/vibration at 4 knots seem kinda slow for resonant vibration?
Hard to say

I sailed with a hydrovane self steering unit that at perhaps 6 knots ..the vane rudder started humming …trailing edge modification solved the problem
 

Zonker

Super Anarchist
10,206
6,399
Canada
Yes, 4 knots would be very slow for resonant vibration in keel/rudder. But yeah possible I guess. Just well below my expectation. Good place to start.

Put your hand on the rigging wires. Are they all about equally tight? Does the sound go away if you hold one? But again - low wind speeds don't usually make the rigging hum though)
 

vibroman

Super Anarchist
I've only experienced notable hums at and above 10-ish knots, but have never sailed a truly high-performance boat. Does a serious hum/vibration at 4 knots seem kinda slow for resonant vibration?
All depends on the stiffness and mass of the foil (this determines the natural frequency). Reducing Stiffness reduces nat freq. Lots of variables to cause that. I had an s20 (4knt shitbox) that would do the same thing
 

Sail4beer

Usual suspect
10,429
3,719
Toms River,NJ
Time to think about altering the aft end of the foils(if that’s class legal). Might be as little as a 1/2 mm needs to be flattened on the trailing edge to break the frequency from resonating.

Eyesailor is correct that the old greeting has finally aged out. There’s a thread in GA for cleavage fans…
 

silent bob

Super Anarchist
8,933
1,443
New Jersey
It hums because it doesn't know the words!


There's a special solution that you can apply to the foils to eliminate the humming:

1 Gallon Gasoline / 4 Litres Petrol

4 Gallons Kerosene / 16 Litres Paraffin

Mix well, Apply liberally, light match, stand back. All traces of the humming will be gone in minutes. Very little effort! Guaranteed to work!
 

10thTonner

Hazard to Navigation
1,730
659
South of Spandau
A longlong time ago I sailed an old Tornado. A certain humming at a certain speed would indicate that the worn-out kickup mechanism was about to spontaneously release a rudder... Good times, except when that happend.
 

guerdon

Anarchist
If you appreciate the sound as an audible low speed indicator similar to a stall indicator on a glider it will dramatically improve your sailing, otherwise bevel the trailing edges of immersed foils.
 

slug zitski

Super Anarchist
7,104
1,469
worldwide
If you appreciate the sound as an audible low speed indicator similar to a stall indicator on a glider it will dramatically improve your sailing, otherwise bevel the trailing edges of immersed foils.
The humming noise gets irritating at high speed

in a gale you are already nervous and listening to all the creaks and grones..that humming adds to the tension and is fatiguing
 




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