Mast Vibration

36041 · Post by **36041** » Fri Apr 15, 2005 7:14 am

Does anyone else get a lot of mast vibration inside the salon area? It only happens when we are at rest, not under load. It takes about 20 knots or so and it doesn't happen all the time, but every once in a while, the mast starts vibrating back and forth.

I don't think the rig is loose and the mast does not appear to be damaged. It's been doing it since we've owned the boat, I'm just now getting around to asking about it.

Any ideas would be appreciated.

Tom

Guest · Post by **Guest** » Fri Apr 15, 2005 10:52 am

Hi Tom, What I thought was mast vibration, was actually vibration of the lower shroud covers. The 5' long plastic roller-covers. I put a bungee cord between port & st'bd shrouds rollers, and it stopped 5 years of annoying noise.
Hope this will work for you, Marc

36041 · Post by **36041** » Fri Apr 15, 2005 1:54 pm

Unfortunately, I can sit under the mast and watch it flex. This is definately the cause of our vibration down below.

Any other ideas?

Tom

doubledutch · Post by **doubledutch** » Fri Apr 15, 2005 2:43 pm

I think what you are experiencing is harmonic vibration which results when the wind speed induces a vibration in the mast as a result of the natural frequency of the mast corresponding to the wind effect. It does not necessarily result from shrouds being too tight or too loose but rather from their particular tension creating just the right conditions for the vibration to get started. You might find that a little variation in the tension from one side to the other may get rid of the vibration or alternatively may change the velocity at which it occurs.

A Nonsuch in my marina had a bad case of wind induced mast whip going on during winter storage whenever the wind picked up a bit. It seemed to go away when the main halyard was anchored off to one side and tensioned a bit. You may achieve a similar result by taking your spinnaker halyard off to one side and putting on some tension. Alternatively you could add a line part way up the mast to induce a little side load when at anchor. What you want to do is upset the harmonic balance so that the vibration doesn't get started. It may take some experimentaion to find the right solution but I would make it a priority as the vibration could weaken the mast over time if left unchecked.

Allezcat · Post by **Allezcat** » Sun Apr 17, 2005 11:49 pm

Allezcat, Hull#10, has an older style mast. With winds above 15Kts from the side (particularly at a dock), the mast "pumps" very noticeably. Sighting up the mast when this is happening reveals the center section of the mast moving side to side. The side stays are as tight as I dare make them without pulling the mast thru the deck. I actually solved the problem by installing new chainplates next to the outer stay plates and rerigging the inner stays to the side of the boat next to the outer stays. this got rid of the pumping but interfered with the jib sheet when close reaching. So I returned the stays to their original location and let it pump!