Mast Oscillations

[Mike Hill]

We have an O'day 35 with a standard standing rig (one upper, two lower shrouds). When docked with winds of 10 to 15 knots on the nose the mast (Isomat) seems to have a resonance point and oscillates (fore and aft) several inches at several Hz at the spreaders. The boat shakes and the internal halyards/cables make plenty of noise. We have purchased a Loos PT-3 tension gauge and "tuned" the rigging and the oscillations remain. Is this a commom occurrence with the Isomat mast or the O'day 34/35? We are out of ideas, any suggestions would be greatly appreciated.

 

[Justin - O'day Owner's Web]

Rigging Issues

Mike,I am not familiar with the Isomat mat per se, but regardless of the spar if you are really getting several inches of movement at the spreaders there is clearly an issue. On your boat, the rig should not bend at all relative to the deck. Modern sport boats have masts that bend off to leward to dump power from full roached mains, but thats a whole different ball game.Some questions:1. What were the Loos readings on the rig?2. When you pull on one lower, does the mid-point of the mast move?3. What type and how old is the rigging?My guess is that the uppers are too tight, preventing the lowers from being set correctly, and thusly allowing play in the mast. I would loosen the lowers, then the uppers, and start over with first the headstay, then the backstay, then the forward lowers, then aft. Justin - O'day Owner's Web