Resonating rigging

[DoubleEnder]

At windspeeds of between about 8-15knots, there is an eerie noise from Nyachilwa's rigging. It's not the screechy sound that you get from all stayed rigs when there is a lot of wind. It's a low volume, variable hum, quite high pitched. It makes 'quiet' nights at anchor or on the mooring really rather unpleasant. I don't like to use earplugs because then I might not hear something important.

The rig is 5/8 bermudan. The mast is hollow spruce. The noise is not made by the runners which are vectran (scarily thin, strong and expensive stuff). I think it is the upper rigging, either the jumpers or the diamonds. Any ideas on how to stop it? It is a really spooky sound, freaks the kids out (and me)

Thank you

Graham

 

[sarabande]

If the hum is variable in pitch, is it smooth as in a glissando, or in stepped harmonics ?

What frequency, as that will give a clue as to the length of the wire or tube involved ?

Does the amplitude vary (the loudness) - unlikely.

Try cutting a curved slot in a tennis ball , and taping it to a section of wire about 1/3 the way along. It should act as a damper to any resonant frequency of that particular section. By elimination you should find which section of wire, if any, is causing the hum. Tightening a wire will change its resonance characteristics.

Other sources could be the mast itself (turbulence across the sail slot; open tube ends of stanchions, spreaders, struts, or similar. If the culprit is an open tube, then a blob of sikalfex or a bit of line will seal it off and stop it.

 

[DoubleEnder]

Glissando

Definitely glissando. There are no slots - the spreaders are all wood, and al I have is a mast track for slides. Though thinking about it there could be open ends on the jumper struts which are steel tubes.......good thinking. Heigh ho up the mast we go. But if it IS the wire, I have a pretty limited range of tensioning, can't make it too loose or tight

But this is useful, thank you very much

Graham

 

[sarabande]

damping the resonance of wire under tension by adding mass, disrupting the air flow, or by an energy absorbing system such as a tell-tale is your most likely way out.

 

[Wansworth]

my father boat had a huM,it was the topping lift under tension after bowsing down the mainsheet,I won 10 quid as solved the prob....he never paid1

 

[Salty John]

If it's not the topping lift you might try wrapping a halyard around the mast from the spreaders down. This seems to disturb the harmonics and silence ensues. I know it sounds daft, but this has cured noisy masts for several boats I've known.