I have experienced the same hum, rattle, and shake on 3 different C&C's over many years of PNW sailing both t anchor and tied to pier. It is my best guess that a cross wind of just the right angle and strength will create the harmonics needed to rattle and shake the rig.
I have tried many different combos of more/less baby stay, back stay, side loads etc to alleviate the shaking. On the 1980 C&C 36 I found a line run aft from the bow, tied around the mast 6' up from the deck reduced the shaking considerably. On Calypso (much larger mast section) the shaking was easier to reduce with more baby stay and back stay tension plus securing the burgee and courtesy flag (when in BC). The burgee and courtesy flags seemed to initiate some of the rig shaking. If your rig has both fore and aft lower shrouds (Calypso and the 36 do/did not) changing the tension a bit on those rig elements may be worth a try. Martin Calypso 1971 C&C43 Seattle ________________________________ From: CnC-List [[email protected]] on behalf of Jim Watts via CnC-List [[email protected]] Sent: Friday, July 31, 2015 7:26 PM To: 1 CnC List Cc: Jim Watts Subject: Stus-List Howling rigging On our latest trip north, we anchored in Clam Bay and had a strange problem. At a certain wind speed, the shrouds would start to hum, sometimes making the boat shake with vibration. The major vibration was felt in the small rod running to the underside of the upper spreaders and in the mast and backstay. I backed each shroud one off half a turn and it really didn't do much except make those shrouds look loose to me, but I'm sure I can't tell the difference of 1/128th of an inch. It eventually faded as the wind dropped. For the next ten days, in all sorts of conditions, we didn't hear it, but when we anchored in the same bay 10 days later, we got it again. Any explanation except witchcraft? Jim Watts Paradigm Shift C&C 35 Mk III Victoria, BC
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