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My rigging is "thumping"!!

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Feb 15, 2005
14
Chrysler 22 Sheepshead Bay Brooklyn, NY
Hi, I have had several suggestions on how to remedy this situation, but so far, no results. My 1977 Chrysler 22 is a masthead rig using 5/32" wire for the stays and shrouds. Under certain circumstances over 8 knots of wind, the rigging (and it seems to be the forestay that has a CDI furler), starts to rythmically "thump" severely. This started happening after I bent on the 150 genoa a few seasons ago. I've used a Loos guage to set the tension to spec,...was told to "crank-down" on the backstay,... increase tension on the shrouds and try putting more tension on the genoa luff. All of this has not helped. Do you have any suggestions? Thank you for your help.
 
Jun 5, 2004
97
- - Greenwich, CT
Thumping in the CDI furler

I wonder if possibly that 150 is lifting up the furler itself, that is the extrusion and drum, which with a CDI furler would be conceivable. I have a CDI furler on my Catalina 22, although I only have a 135. I can see this lifting of your CDI furler as possible with 150. You will probably have to just look at the drum as you sail and hear thumping to confirm this.
 
Feb 15, 2005
14
Chrysler 22 Sheepshead Bay Brooklyn, NY
Thanks for looking..

The "thumping" is most definately a sound made by the forestay snapping fore and aft (like a guitar string) causing the genoa to "thump". The sound is not metallic, but more resembles the sound of fabric flexing. So far, the only way I can releive this is to fall off the wind just a bit or ease the genoa. Oh, did I mention that the "thumping" occurs when I sail close hauled? Thanks for the input. Happy Sailing
 
B

Brion Toss

Meet Mr. Vortex

Hello, You are experiencing the effects of vortices, combined with harmonic lengths and masses, and almost certainly combined with being parked in a marina, approximately sideways to the wind. When the wind hits an object (the mast, or perhaps in this instance the furler), it creates little vortices on the leeward side as it goes by. These vortices create a partial vacuum, which collapses and reforms at a rate determined by windspeed and obstacle size and shape. If the rate that the vortices collapse and reform is harmonic with the length and mass of the object, you get variations on the thumping you describe. Annoying, isn't it? The bad news is that the problem is not much susceptible to changes in tune. The good news is that it is very unlikely to happen when you are at anchor, or parked head-to-wind in a marina. And there are other solutions to it, like hoisting a cloth square, wrapped over the stay, with grommets on the corners for attaching lines, on the spinnaker topping lift, with a downhaul made off at the base of the mast. Tension the lift, and the stay and mast will stop oscillating. Fair leads, Brion Toss
 
Feb 15, 2005
14
Chrysler 22 Sheepshead Bay Brooklyn, NY
Gee! You sound just like my old Physics Prof.

I was hoping it wasn't a harmonics problem only because I realize I can't "tune-out" a harmonic frequency. Instead of a square piece of cloth, could I hang out a bra..so at least the guys at the Club will think I'm still "with-it"?....at least while I'm sailing. At my age I could use an ego booster! Thanks for responding and Happy Sailing.
 
B

Brion Toss

Oops

Hmm, Not vortices. Too bad, I love that one. What tension do you have on the backstay? Could it be that drum lifting? Have you examined the connections aloft and alow? Yours, Brion Toss
 
Feb 15, 2005
14
Chrysler 22 Sheepshead Bay Brooklyn, NY
Thanks Brion, but take a look at reply #2.

I still like the Bra idea though!!
 
Jun 5, 2004
97
- - Greenwich, CT
Toggle on top of forestay?

Since you have a furler, do you have a toggle at the top on your forestay? Most furler manufacturers recommend this installation. Without this toggle, you may indeed experience this thumping.
 
Feb 15, 2005
14
Chrysler 22 Sheepshead Bay Brooklyn, NY
I installed the CDI furler as instructed and...

to be honest, do not recall seeing a need for a toggle. There is some up-and-down freedom of movement for the entire unit, but I don't see how this could set-up this rhythmic soft sounding "thump". I guess I'll just have to live with it, as long as it's not causing any problems. Thank you for your replies. I do appreciate them.......can I still fly the Bra off the forestay,....please?
 
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