Rig (and boat) vibrating when the winds get up

[truscott]

We replaced all the standing rigging in 2012, and had it all tuned up by the riggers. All has been well until this season, when I noticed that in certain conditions the boat gets a vibration through it. It's sort of like the surging sensation you get when tied stern to and a ferry goes past. I noticed also that on Starboard tack, my port aft lower was slack, whereas on Port tack, my Starboard Aft lower stayed pretty tight. My back stays felt quite loose, and so I resolved to tighten everything up, figuring that there had been a fair amount of stretch etc... over these last few seasons. Whilst doing this I noticed that my rigging screws were all pretty much out of whack with each other, and so I tightened and loosened accordingly, keeping an eye on keeping the mast straight, a little aft rake, pre-bend etc...

Now, whilst sitting moored up in the harbour, the vibration/pumping/whatever is happening whenever the wind blows.

I had Vyv Cox moored alongside and we had a bit of a chat, and he thought it might be because the rig was too tight, but my back stays do not feel that at all (I can easily move them together by several inches!). Could I have overtightend my Cap shrouds etc.. ?

Interested in the panels view (all my previous tuning experience has been on Fractional rigs, with the exception of a friends cat that I looked after for a number of years, and that didn't have back stays).

Cheers, PT

 

[sailorman]

Vibration might be the topping lift
the rig needs adjusting as the wires will have slackened after the initial setting up
selden have "how to " on their site

 

[vyv_cox]

Hi Paul, your backstay is considerably slacker than mine, which I know is close to the maximum loading allowed by the wire size. I didn't check your shroud tension, so cannot advise there. The comment about high tension relates to the fact that compressing a strut, in this case the mast, allows it to deflect laterally with far less force, for example vortex shedding or other wind instability. It is clear that in your case there is not all that much compression in the fore and aft plane so I doubt if this is the cause. The Selden rig tuning guide might prove useful and I have a simplified version of my own on my website. Cheers, Vyv.

 

[Vegable]

Had this on mine last year and the beginning of this year. It made a fast "choffing" type noise and the boat vibrated. I solved it by tightening the lower forestay - don't know its correct name.
Had several experiances of topping lift vibrations but that tends to be a "humming" noise, a more musical note.
Mike

 

[Daydream believer]

Vibration might be the topping lift

On my boat I have a short strop & hook fitted to the backstay to hang the end of the boom when not in use to take tension off the topping lift. Stops most of the noise

 

[truscott]

Cheers Vyv! I have been having a read of your version and will look at the Selden site too. The going for a sail part is slightly complicated as you can imagine (you missed out on the couple of scroates trying to nick our bikes at 3am which has rather soured our little sojourn here, so we may well be sailing north pretty soon (the PP already suspect who it was and have asked us to go do an ID later today)). In the interim, I plan to release all the tension on the backstays and then do the two meter tape measure trick. We're in for a blow today or tomorrow so it should soon prove/disprove my theory.

Hi Paul, your backstay is considerably slacker than mine, which I know is close to the maximum loading allowed by the wire size. I didn't check your shroud tension, so cannot advise there. The comment about high tension relates to the fact that compressing a strut, in this case the mast, allows it to deflect laterally with far less force, for example vortex shedding or other wind instability. It is clear that in your case there is not all that much compression in the fore and aft plane so I doubt if this is the cause. The Selden rig tuning guide might prove useful and I have a simplified version of my own on my website. Cheers, Vyv.

 

[truscott]

Thanks for the suggestions on the topping lift, although this isn't a factor when we are sailing (when the issue first appeared) as we usually have it a little loose when the sails are up.

We have had the topping lift humming issue in the past, so I don't over tighten that now, and as we have a Selden strut, it isn't needed for holding the boom up anyway (I lash the boom over to one side also, so don't need to hoik on the mainsheet either).

Cheers, PT

 

[DanTribe]

My rig is very prone to this vibration problem in certain conditions, usually light to moderate beam winds.
I try all the obvious options, i.e.. tighten, loosen backstay and mainsheet, towel tied to topping lift etc. This sometimes works but usually not for long.
One trick which sometimes helps is to hoist a mooring warp up the mast then spirally wrap it around the mast. I assume that this helps to vortex shed like the fins you see on tall chimneys.

 

[BurnitBlue]

Another trick popular in Sweden is to hoist a narrow mini mainsail (about 5 cm wide strip) up the mast. I have seen it used both with luff groove or slides. This also breaks up the airflow that causes the pumping.

 

[truscott]

My issue with the vortex theory is that it was also happening while we were sailing. I ended up using a tape measure to mark off 1 meter and then tightened the back stays up to give me 30% of max. The pumping seems to have gone but then we also haven't had much wind yet. Forecast is for a blow today, so will be watching with interest.

 

[contessaman]

My old boat used to get mast pumping under certain conditions because all the stays were in line. It happened when the wind was abeam in the marina. Somebody explained it was because of rotor streaming. Anyway, the cure is to wrap a halliard around the mast in a spiral. It breaks up the airflow. It's the reason some tall industrial chimneys have a spiral around them. Give it a whirl (no pun intended) it worked for me. Does sound like something has changed though when your rigging was *tuned* just because it was done by an expert don't assume it's been expertly done...