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Old 29-05-2020, 09:46   #1
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Noise/Vibration with partially furled genoa

Hi, I'm a novice sailor on the SF Bay and I have a (possibly dumb) question about my Harken MKI fuller and genoa. It is a 130% genoa and I typically have it fully closed or fully opened. Yesterday I got caught unexpectedly in 20 knots and was having trouble handling things so I took the genoa in about 50%. The reduced sail area drastically improved things but there was a strange sound/vibration.

When partially extended, at least to the degree I had it yesterday, there was what sounded like a metal can rolling and the entire boat was vibrating. Initially, I thought some anchor chain might be getting rocked around below deck but it became apparent that whatever the source was, it was related to the genoa. Looking upwards, there was nothing that appeared to be rubbing, shaking, nor caught and we couldn't pinpoint the exact source of the sound but I'm wondering if it came from the furling drum.

This does not happen when the genoa is fully extended. I was going downwind on the genoa alone (no main.) I did not adjust the sheet angle -- the sound/vibrations gave me pause and I ended up taking it in rather than play with things and risk potential damage until I better understood the nature of the issue.

Is there something special that needs to be done if not unfurling a genoa fully? If not, is there a maintenance process I can use to rule out potential issues with the furling drum?

I tried searching but I'm at the point where I don't know what I don't know so am not sure what keywords to use. I appreciate any advice or ideas you may be able to share. Thanks!
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Old 29-05-2020, 09:51   #2
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Re: Noise/Vibration with partially furled genoa

What you've found is a resonant frequency. All physical objects have them, and some such as the Tacoma Narrows Bridge and the early Comet airliner self destruct thereby. On this forum, the most usual is standing rigging or halyyards, which at certain tensions resonate just like piano wires. AD or subtract a bit og jenny, and it will go away.

If you need more help with the principles involved, say so and I'll pontificate.
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Old 29-05-2020, 10:07   #3
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Re: Noise/Vibration with partially furled genoa

Thank you very much! I'll read up on content with those keywords and if I hit it again, play with the adjustments until it goes away.
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Old 29-05-2020, 10:40   #4
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Re: Noise/Vibration with partially furled genoa

In addition to the amount of sail, other variables that might need attending to are the rig tension, and halyard tension.

I don’t doubt under exactly the right conditions, it is possible for a partially furled sail with a properly tuned rig to vibrate like you describe, but I have never seen it happen. If you are not sure your rigging tension is right, it might be time to have it checked, or learn how to check it.

A fully furled sail can do this (and many do!), but the physics of that do not apply to a deployed (even partially) sail.
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Old 29-05-2020, 11:36   #5
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Re: Noise/Vibration with partially furled genoa

OK, thank you for that. I will read up on rigging tension as well!
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Old 30-05-2020, 09:11   #6
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Re: Noise/Vibration with partially furled genoa

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Originally Posted by SeaHarlequin View Post
Hi, I'm a novice sailor on the SF Bay and I have a (possibly dumb) question about my Harken MKI fuller and genoa. It is a 130% genoa and I typically have it fully closed or fully opened. Yesterday I got caught unexpectedly in 20 knots and was having trouble handling things so I took the genoa in about 50%. The reduced sail area drastically improved things but there was a strange sound/vibration...............
You did not say what sailboat manufacturer, model and length. 130% head sail is really large for the SF Bay and yesterday was really windy as I was on my boat in Point Richmond!! At 20+ knots we reef our 110% jib and still get plenty of power without vibration and noise. Your head sail may be designed with a limited reefing range. In that case take the head sail to a local sail loft to have them modify it to improve reefing OR purchase a 110% head sail. This should eliminate the vibration and noise.
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Old 30-05-2020, 09:23   #7
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Re: Noise/Vibration with partially furled genoa

Was your jib leech vibrating? If so, tighten the leech line.
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Old 30-05-2020, 11:05   #8
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Re: Noise/Vibration with partially furled genoa

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Was your jib leech vibrating? If so, tighten the leech line.

Imo the most likely cause/remedy.
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Old 30-05-2020, 11:36   #9
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Re: Noise/Vibration with partially furled genoa

I read and do not understand. The leech would be easy to notice but it does sound differently.


b.
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Old 30-05-2020, 11:45   #10
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Re: Noise/Vibration with partially furled genoa

Quote:
Originally Posted by tkeithlu View Post
What you've found is a resonant frequency. All physical objects have them, and some such as the Tacoma Narrows Bridge and the early Comet airliner self destruct thereby. On this forum, the most usual is standing rigging or halyyards, which at certain tensions resonate just like piano wires. AD or subtract a bit og jenny, and it will go away.

If you need more help with the principles involved, say so and I'll pontificate.
Yup, I remember my stays singing in around 60 knots. Resonant frequencies can be harmful to hardware for too long a period of time though, so he should try to avoid them.
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Old 30-05-2020, 11:48   #11
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Re: Noise/Vibration with partially furled genoa

Could be the mast pumping, what's your rig tension like ? Were the leeward shrouds slack when this was happening ? Common here is to refer to a loose tune as "San Diego" style and "San Francisco" is much tighter.
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Old 31-05-2020, 07:05   #12
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Re: Noise/Vibration with partially furled genoa

When you partially furl the genoa, the pull angle of the genoa need to be adjusted by pushing forward the genoa car so the sail will still pull correctly. If you don't adjust the pulling angle of the furled genoa it will vibrate and induce all sort of noises.
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Old 31-05-2020, 07:23   #13
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Re: Noise/Vibration with partially furled genoa

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Originally Posted by Elie View Post
When you partially furl the genoa, the pull angle of the genoa need to be adjusted by pushing forward the genoa car so the sail will still pull correctly. If you don't adjust the pulling angle of the furled genoa it will vibrate and induce all sort of noises.
That is true, but it is because of the apparent sail area relative to the wind. Vibrations are caused when the frequencies of the wind match the harmonic frequency of the given area. Changing the angle, tension or relative size of the sail will also stop the resonance.

This video deals with that in a more simple format, but that mathematics are the same -
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Old 31-05-2020, 09:59   #14
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Re: Noise/Vibration with partially furled genoa

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Originally Posted by sail sfbay View Post
You did not say what sailboat manufacturer, model and length.
Sorry about that, I should've thought to include that. The boat is a 1974 Ranger 29'.

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Originally Posted by sail sfbay View Post
130% head sail is really large for the SF Bay and yesterday was really windy as I was on my boat in Point Richmond!! At 20+ knots we reef our 110% jib and still get plenty of power without vibration and noise. Your head sail may be designed with a limited reefing range. In that case take the head sail to a local sail loft to have them modify it to improve reefing OR purchase a 110% head sail. This should eliminate the vibration and noise.
I have a 130% head sail because that's what came with the boat. The sailing instructor I was working with said it was too large but I figured I could just reef it in. It didn't occur to me that a furling genoa had "reefing" ranges. I'm still learning and this is very helpful -- I'll pay more attention to how the genoa responds at different stages of unfurling (in much calmer winds!).

Quote:
Originally Posted by sail sfbay View Post
In that case take the head sail to a local sail loft to have them modify it to improve reefing OR purchase a 110% head sail. This should eliminate the vibration and noise.
That's a good idea; I'm already looking for a loft to add a reef point in the main, maybe I can have them look at the genoa to improve reefing after I've gotten a better idea of what's going on. Thanks!
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Old 31-05-2020, 10:02   #15
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Re: Noise/Vibration with partially furled genoa

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Originally Posted by rhpike View Post
Was your jib leech vibrating? If so, tighten the leech line.
Not that I noticed; the leech line was pretty taut from what I recall. I'm still learning so it's possible I missed something like that. I'll add the leech line to my list of things to monitor when I try to duplicate the issue next time. Thanks!
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