Middle mast wobble....86' N27 - SailNet Community
 
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post #1 of 7 Old 04-08-2009 Thread Starter
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Middle mast wobble....86' N27

I get some weird wobble in the middle of my mast. Happens at the dock and also while under engine power. Just needs some wind and it starts-a-shimmyin... Ive tuned and re-tuned the stays. Just won't go away. Sooner or later its going to start compressing my deck.

Anyone have this problem??
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post #2 of 7 Old 04-20-2009 Thread Starter
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Nothin' huh? Not even one little, tiny hint???

I'll even take an uneducated guess......
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post #3 of 7 Old 04-20-2009
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It would seem you are correct, that no one here has seen this problem. I've sailed Oday daysailors, Soling 27's, Seafarer 22's, J24's, Olsen 25's, C&C 30's, J30's, C&C 40's, S&S 46 one off's, and never encountered it. I would recommend having a professional rigger look at it. You are not going to compress the deck, as the boat has a compression post from the deck to the keel. But your concern that you might makes me think your tension may be too tight, and you may be straining the chainplates. I suspect your tuning is not quite right. Too loose? Too tight? I can't say. Getting professional help is a small price to pay to solve this kind of problem.
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Michael
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post #4 of 7 Old 04-20-2009
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It's not unusual, especially with in-line shrouds, to have a mast "pump" under certain wind conditions as you describe. It may be due to too much tension, or too little. Often Babystays were used to discourage this problem.

Double lower shrouds can be adjusted to stabilize the middle of the mast, but I believe your rig has single in-line lowers so you won't have that option.

It may be something you'll just have to live with unless you're willing to add a babystay.

Ron

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post #5 of 7 Old 04-21-2009 Thread Starter
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Thanks guys! I was beginning to think that I had some un-curable problem. I guess I'll just loosen them (i do have babystays) and slowly tighten them up over a period of time to check if it will work.
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post #6 of 7 Old 04-21-2009
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It is not unusual for a mast at rest to develop a harmonic motion from wind blowing at the right speed from the right direction. It is not a problem, other than providing an irritating distraction. You shouldn't mess with your standing rig to try to remove it, as you want your rig set up right for its primary purpose. you may find adding/removing backstay or babystay tension tohave an effect, or try adding some tension to the middle of the mast by tensioning a main halyard forward under a spreader root, anything that disrupts the harmonic balance.

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post #7 of 7 Old 04-23-2009
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Uh; those "babystays" are actually your lower shrouds. The N-27 does not have a "babystay" which goes from the front lower 1/2 of the mast down about 1/3 forward on the foredeck.

The lower shrouds will help stabilize the mast fore/aft a bit but really they are to help adjust mast rake and/or bend. I had a similar problem on my N-41 and it turned out that the lower diagonal shrouds (lower primaries) were loose. To tighten those I had to go up to the first spreader and tension the diagonals. Don't do this unless you have a good tension gauge like a loos gauge or similar tool.

Your mast is under way more compression while you are sailing so I would not worry about causing the deck to dish with the turnbuckles. But again; be sure and use a good tension gauge and follow the directions for basic rig tune. In addition you should check for changes in rig tension over time. If the shrouds get loose after sailing it could either be stretching or failing shrouds, or compression of the step due to core rot, chainplate rot/failure, or failure of the keel step.

If everything is tight you could still have some harmonic wiggle of the mast depending on wind speed; but it should not shake the boat violently.
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