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Rig Shimmy

Artey1

.
Jul 18, 2019
125
Hunter 34 Oklahoma
Firstly - I'm in Oklahoma and there are no riggers near me.

I have a 1984 Hunter 34 with a B&R rig, with split backstay. We were sailing in 15 - 20 kts with gusts up to around 25. We would get this shimmy the whole time that I have never seen or experienced on the boat before. The spreaders would shift fore and aft in a twisting motion around the central part of the spar, that was honestly down right scary. I have a Loos gauge for the rigging and have put it on the rigging and while it is not perfectly aligned and I need to spend more time evening up port/starboard as well as do the halyard measurement it was not that far out. The D1s and D2s where right around 8 - 10% breaking strength.

We were flying full sail, traveled down and twisted off, and flying our 110 jib. We normally fly a 135 jib and had changed to the smaller headsail for the first time since owning the boat before our race due to the forecasted higher winds/gusts that day. We ended up finishing our race, but I want to figure out the cause of this before going out again.

Boat was last hauled a year ago and stepped and tuned with the loos gauge except for the forestay which can't be gauged because of the furling extrusion over it.

Any thoughts? My first thought was I may have developed some stretch on the forestay or diamond stays causing the shimmy?
 
Feb 21, 2013
3,456
Hunter 46 Point Richmond, CA
What do sailboats and guitars have in common?.............. they both have tight strings (shrouds), necks (mast) and acoustic chambers (hulls)......add a little wind to activate the strings and music is made. Lots of places to look like discussed in this thread: Rig vibration during sail and at dock? | SailNet Community Do a search on this forum on " rig vibration causes" and you will see many threads covering this subject with potentail solutions Search results | Sailboat Owners Forums. Please share what you learned.
 
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Johnb

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Jan 22, 2008
1,286
Hunter 37-cutter Richmond CA
What you described sounds more like mast pumping. It can be scary. Suggest you google that
 
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Artey1

.
Jul 18, 2019
125
Hunter 34 Oklahoma
What you described sounds more like mast pumping. It can be scary. Suggest you google that
Yes the more I have read about it I think you are right, and it was definitely scary! Though I made sure to swallow my fear for crew's sake and took pressure off the boat until we were back at the dock. I am going to go back to the basics tomorrow/this weekend and check the pre-bend, rake, and retention evenly the shrouds, then go up and do a full rig inspection to make sure I have no broken strands or cracking anywhere and then sail her conservatively to see how things are. That's all I can really come up with since there aren't riggers in my area. I may try to get a phone consult with one or something at least to help guide me. I'm capable but don't like guessing at things or think I know just because I've read some online manuals or guides on something this important.
 
Oct 26, 2010
1,378
Hunter 40.5 Beaufort, SC
Firstly - I'm in Oklahoma and there are no riggers near me.

I have a 1984 Hunter 34 with a B&R rig, with split backstay. .... The D1s and D2s where right around 8 - 10% breaking strength.
My Selden tuning guide says to tension to closer to 15% to 20% of breaking strength. 8 to 10% seems a little low. Google Selden Hints and Advice and you should be able to get the tuning guide. The final tuning is done when underway in a moderate breeze.

Did you happen to notice if your lee shrouds were slack when all of this was happening?
 

Artey1

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Jul 18, 2019
125
Hunter 34 Oklahoma
Smokey my port shrouds were definitely more slack than I have noticed in the past. Moreso than the starboard side and when on a starboard tack is when we would get most of the pumping. That's why I was so surprised when I put the loos gauge on them. They were within 1-2% of each other from port to starboard. I was expecting 5 or more percent difference based on the movement fore to aft I was seeing in the spreaders.
 
Nov 26, 2012
1,511
Hunter 34 Berkeley
Mast pumping is likely the result of the lowers being a little too loose allowing the mast to vibrate in its Phase I natural frequency. Tightening the lowers should stop that.
 
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Oct 26, 2010
1,378
Hunter 40.5 Beaufort, SC
@Artey1 One thing that can cause loosing of the rig is hull flex as well as chainplate pulling up so I'd check that very carefully too. They will inherently be within 1 or 2 % of each other since each side impacts the opposite side. When you tighten one, it tightens the other but it may pull the mast out of alignment. Look at the Selden Tips and Hints. That is why you have to set it up and make small adjustments on each side while checking the mast alignment.
 
Jun 8, 2004
8,856
-na -NA Anywhere USA
Artery

B&at style masts were generally no backstay masts but it would help if you could verify by markings.

What furling system do you have as most systems will allow for you to access the forestay turnbuckle. Then maybe an owners manual can be found.

Can you post a side photo of the mast to see how much prebend and rake you have?

Just to be sure, did you notice any slackness of the lower shrouds under sail?

As suggested Check all of your chain plates that they are secure and advise
 
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Oct 26, 2010
1,378
Hunter 40.5 Beaufort, SC
@Crazy Dave Condon I am sure as a former dealer you are a lot more informed about the Hunter rigs than most, if not all of us. I have a 1994 Legend 40.5 and I have a backstay. It does have swept back spreaders and the rig will "stand" without the backstay attached (I had to do this to get it into the lift for hauling). I don't know if its an "early generation" B&R rig or some hybrid. It is a Selden mast and boom. I've always wondered if it was truly a B&R or something "in between." It is a fractional rig with two spreaders with "continuous" shrouds D1, D2 and D3 only. No diagonal stays like I see on the newer B&R masts with no backstay. By the way - I like the backstay - just makes me feel more secure ;).
 
Last edited:

Artey1

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Jul 18, 2019
125
Hunter 34 Oklahoma
Dave - this is on a 1984 Hunter 34 so it is a B&R masthead rig with split backstay.

The furling system is a Harken Unit 1 - super old not made anymore original to the boat. It does allow adjustment but the forestay turnbuckle access requires pulling the jib down and sliding parts of the drum down/extrusion up the forestay to access it - so I will be having a look at that this weekend when I am at the boat.

Will definitely get a photo when at the boat and post up for everyone.

10-4 on the chainplates, I also had this realization and actually have some inspection ports installed to look at them where they are installed between the hull and liner and will be poking my camera through them to see if there is anything amiss.

Mark - thank you for that information! The V1 lower on the port side was definitely the most loose thing on the boat when I checked with the Loos gauge - glad to hear validation that this may be the biggest cause for issue.

It sounds like overall that my rig was on the loose side anyways when originally set, it was set at like 10-12%. I stopped going further because I had done compression post and chainplate jobs when on the hard before stepping the mast, and having never tuned a rig before in my life, it felt very tough to continue turning the turnbuckles and I didn't want to break anything, so I figured in some months after sailing the boat I would come back to it and basically never did until now when I have the pumping issue showing up. So maybe just time to readjust things since some of those major jobs from being on the hard.
 
Jan 7, 2011
2,776
Oday 322 East Chicago, IN
I didn’t think a B&R rig used a backstay…my 1996 Hunter 280 didn’t have one.

Greh
 
Jun 8, 2004
8,856
-na -NA Anywhere USA
In 1984 Hunter was using Kenyon Isomat masts and booms but later Z Spar and then
Selden after Z Spar made a bad move regarding the large masts. I wonder if the mast had been replaced but see if there are any mfg decals on the mast and boom
 

Artey1

.
Jul 18, 2019
125
Hunter 34 Oklahoma
In 1984 Hunter was using Kenyon Isomat masts and booms but later Z Spar and then
Selden after Z Spar made a bad move regarding the large masts. I wonder if the mast had been replaced but see if there are any mfg decals on the mast and boom
My mast and boom are Kenyon
 
Jun 8, 2004
8,856
-na -NA Anywhere USA
I too associated B&R rigs with no backstay thinking the 23.5 was the first without a backstay until I remembered the 18.5 Hunter which came out in the late 1980’s did not have a backstay. Many day sailors do not have a backstay.
 

Artey1

.
Jul 18, 2019
125
Hunter 34 Oklahoma
Saturday I did more investigating and started rig tuning. I started by measuring out the prebend using my main halyard tied off and pulled as tight as possible to the base of the mast. While I didn't climb to measure by eyeball it is 5-6" of pre-bend.
Pre-bend.jpg

Then measured rake using a 7 lb hammer as a plumb bob. Before adjustments its was like 10" of rake!!! This pic is not actually measuring rake but tried to get the whole mast in the pic to hopefully show it.
Mast pre-bend.jpg

Then I removed the jib and detached the furling line and securing my jib halyard and spin halyard to the bow cleats, not super cranked down but just enough that if something were to happen I wouldn't have my mast fall backward on me. Also make sure to have mainsheet and vang eased off. From here, I took the torque tube off of the furler and loosened the big nut under it and the locking nut under the drum. Took 2 turns off of each turnbuckle on the backstays and put those same turns on the forestay. My furler is the Harken Unit 1-1841. Its manual states that there should not be more than 2 1/4" of threads showing on bottom or top of its turnbuckle. I made sure to stay within this measurement and slowly kept adjusting backstay and forestay until I had about 6-7" of rake and a fairly tight forestay.

Then I put as much tension on the backstay as the old stretched rigging allowed me, but was only about 10% of breaking strength. I'm certain this has to be original rigging which unfortunately for me is a problem I will have to stow for another day. I did go up the mast and fully inspect looking for broken strands, cracking etc... nothing visible, but at next haulout I will hopefully get to plan for a new standing rigging.

I then sighted to make sure that mast was straight athwartships. From best I can see it was.
bow.jpg Stern.jpg

From there I took my loos gauge and took measurements of my V1, V2, and D1 stays. I started with the V1's and adjusted them to about 15% breaking strength of the 1/4" wire. Since my furler/forestay was tight at this point I removed my jib and halyard and spin halyard from the bow cleats. I used the jib halyard to measure port and starboard below the shear line/toe rail on each side at the stays and compared. Less than 1/2", so I was in the clear. Next V2's, same thing, except after measuring with the jib halyard again. I put the loos gauge back on the V1s, and too my surprise they measured tighter. So I adjusted V1s again, then back to V2s until I was happy with the loos gauge measurements. Rinse and repeat all this with the D1s. The D1s on these boats are actually slightly bigger than 1/4" and my loos gauge only goes to 1/4" but the wire will still fit in the plastic clip to measure. I know the breaking strength indicator will be off as it showed 40 on the gauge which equates to 20% break strength on the 1/4" wire. So for a bigger wire this will actually be less, I just don't know how much less - so I adjusted them to be equal readings at 40 on the PT-2 gauge and made sure they were firm. Re-measure all the stays again, and walla, done.

From here I need to sail it and fine tune/adjust more in the standard about 10 kts of wind, take any slack out, etc... but I was solo and thats a hard feat to single hand and make adjustments with no auto pilot. I'll have to wait for my wife to join me next weekend to see if my hard work paid off. The heat index was only a breezy 110* :redface: so I called it a day and am ready for this next weekend to see the results!
 
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