Vibration under Sail just over 4 Knots

[Evo18]

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]

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]

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]

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]

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]

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.

 

[vibroman]

ha
batting 500 .... its trailing edge an exciting the nat freq

 

[Marty Gingras]

ha
batting 500 .... its trailing edge an exciting the nat freq

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?

 

[slug zitski]

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]

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]

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]

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…

 

[beercanned]

We get the same on Open 5.70s.

A quiet, low-tone hum at ~ 6kts, a mid-tone hum at ~11kts, and somehow the foils go quiet at more than 15kts.

Never bothered worrying about it.

 

[PurpleOnion]

Mine kicks in between 8.5 and 9.5 knots and lets me know things are about to get really fun. I would chamfer the trailing edge, but I've grown to love that hum.

 

[slug zitski]

Sometimes the hum is educational

you know you have just hit “that speed”

same with the break of your stern wave …” that speed “

 

[silent bob]

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!

 

[Sail4beer]

It might be quicker with tannerite.

 

[10thTonner]

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]

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]

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