Huh. Maybe it is the keel. If there’s slack between the keel and the keel pin I suppose the turbulence could cause it to vibrate.
But I think your keel is like mine, > 500 lbs. Hard to imagine a big heavy lunk like that vibrating much.
Yup,~500lb keel. I don't know what could have caused it. Weather's been bad so I can't get my boat out and I've not had a chance to do much work. I got a new 4-pin deck plug and wired it but that's about it. If weather cooperates then this weekend I'll try to set up my new boom vang and see about installing the deck organizer system I'll be using to route my halyards to the cockpit. If nothing else I'll finish my mast raising system.