Topping Lift Vibration - SailNet Community
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post #1 of 14 Old 05-15-2012 Thread Starter
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Topping Lift Vibration

When the wind is at just the right speed, it hums through the mast and is much louder than I'd like to tolerate. I figured out that the line that's causing the vibration hum is the topping lift, so I'm not sure how to make it stop (can't exactly remove tension from that one). But I'm still green to sailboats. Is there anyone out there who can help me get rid of the Humming Mast?

For reference, I have an Islander 30, and don't have anything to rest the boom on to relieve tension from the topping lift's line.

UPDATE: Tried manipulating and taking weight off the TL, but the mast is still humming, so that's not the issue after all. Any ideas what else could be making the humming, besides lines running through it? I've played with different tensions with the other lines and nothing is working. I'm going crazy here!

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Last edited by cktalons; 05-15-2012 at 06:37 PM. Reason: Changing information
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post #2 of 14 Old 05-15-2012
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Topping Lift Vibration

Hi. I assume you are talking about this happening while sailing with the main up. True? Not sure about the Islander but most boats don't need the topping lift rigged with the main up. Removing the topping lift and securing it to the mast may help and eliminate the noise and vibration.
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post #3 of 14 Old 05-15-2012
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Re: Topping Lift Vibration

Courtney, My main topping lift has the same problem, if its tight it hums a tune...I can ease it off a bit as I have a 2nd lift from the mizzen holding the main boom. Perhaps try easing the main sheet BILL

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post #4 of 14 Old 05-15-2012
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Re: Topping Lift Vibration

topping lift should be loose when sailing. The sail won't have the right shape and may even be like a big pocket to the wind with the TL holding the boom up.. Hum could be the boat telling you more speed! LOL

Denise, Bristol PA, Oday 30. On Tidal Delaware River, Anchor Yacht Club.
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post #5 of 14 Old 05-15-2012
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Re: Topping Lift Vibration

Experiment with tension of the lift (via topping lift itself or mainsheet tension as mentioned) to see if you can tone it down.... Change the wire/line whatever to a different size perhaps..... Fashion a temporary crutch, or a short strop to the backstay to support the boom and get the tension off the normal topping lift.

I'm assuming this is while not sailing, as otherwise the TL should be slack, as mentioned above...

Ron

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post #6 of 14 Old 05-15-2012 Thread Starter
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Re: Topping Lift Vibration

The mast hums when at anchor, yes. It doesn't make a sound when sailing, as my boat doesn't have a vang, therefore the TL is loose. The only sound I hear then is the whooshing sound in the wind and the splashing against the hull, in other words, absolute heaven.

Chris12345, I'm going to play with it and see what I can do, but if I can't get it to stop humming, do you have any musical requests?

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post #7 of 14 Old 05-18-2012
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Re: Topping Lift Vibration

I've got to think that since it's not the TL, you've got to see if your rig is properly tensioned. But I'm no expert....

Cute sheltie - I raised two of them
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post #8 of 14 Old 05-18-2012
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Re: Topping Lift Vibration

If no one else has taken it, I guess I will:

How do I stop my mast from humming?

Teach it the words!

Zen Again

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Testing a mother's love since 1962
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post #9 of 14 Old 05-18-2012
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Re: Topping Lift Vibration

Tie a line around the topping lift about 2 feet above the boom and then to a winch on the coach roof. Put a little tension on the line and the harmoinics should stop - works for me.
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post #10 of 14 Old 05-18-2012
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Re: Topping Lift Vibration

In all probability, the MAST is vibrating due to an induced harmonic vibration that is 'exciting' the 'natural frequency' of the mast. This is what causes adjacent strings on a musical instrument to vibrate ... or what causes a violins strings to vibrate when rubbed with its bow.

To stop the vibrating at this 'node' of natural frequency you will have to change the natural frequency of the mast ... either by changing rig tension, adding MASS to the mast, or (most commonly) by 'bowing' the mast.

Artificially bowing the mast (called 'prebend') will increase stiffness and most importantly changes the 'natural frequency' of the mast. 99% of all mast manufacturers specify that proper mast set-up include this 'pre-bend'.

Standard and 'proper' prebend is: 3/4" forward bowing (prebend) on a single spreader mast OR 1/2" prebend for EACH spreader set on a multiple spreader rig.

•This is 'easy' to do on masts with lower forward and aft stays ... simply increase the tension on the forward lower shrouds and decrease the tension on the aft lower shrouds while sighting up the front of mast until you get the 'correct' PREBEND.
•If the boat has running backstays, simply apply tension to the runners.
• If the boat doesnt have lower foreward/aft stays, then you will have to radically change the backstay tension or install running backstays (or hang a weight on the mast, etc.). alternatively as a temp. 'remedy' when moored or docked, simply loop a jib sheet around the cap shroud and put a little bit of winch tension onto the jibsheet --- temporary solution.

A mast that constantly 'sings' / hums due to an induced excited 'natural frequency' will soon cause the rigging terminal connections to FAIL by fatigue failure. If the oscilations become very extreme (mast *pumping*) the mast vibrations can cause the rigging terminals and wire to fail by tensile/ductile failure (impact).

Last edited by RichH; 05-18-2012 at 12:05 PM.
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humming mast , mast hum , topping lift

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