Mast pumping?

[sam1939nl]

My O day 30 sometimes will have a viberating and pumping motion to it's mast and rigging when at dock or when at anchor, seems to occure when wind is a certain way over the deck , easing main sheet will lessen it some times. Do any one have a segestion as to it's possable cause and or remedy.

Sam

 

[Migrant III]

My O day 30 sometimes will have a viberating and pumping motion to it's mast and rigging when at dock or when at anchor, seems to occure when wind is a certain way over the deck , easing main sheet will lessen it some times. Do any one have a segestion as to it's possable cause and or remedy.

Sam

Had similar problem on a Northern 26 - installed SS 1/2" bar screwed into keel and bolted to deckhead beside the keel stepped mast. Worked great. The real vibration for that boat was sailing in a strong wind, or, as you experienced, a really strong gust across the slip

 

[sam1939nl]

Had similar problem on a Northern 26 - installed SS 1/2" bar screwed into keel and bolted to deckhead beside the keel stepped mast. Worked great. The real vibration for that boat was sailing in a strong wind, or, as you experienced, a really strong gust across the slip

Thank you!
But that remidy may not be possable with the O day 30 because the keel is incapulated into the hull fiberglass and the mast is stepped onto a flanged plate in the bilge (no keel bolts are used) I don't think that the mast can move. It seemes that the topping lift is acting like a pinao string.
This only occures when the Main sail is down and furrled on the boom.
sam