My boat, a Gulfstar 37, has developed some sort of rig problem. It's been off and on for a couple years, and I've tried a few things to fix it, but lately it's become much more common. So what happens is I'm just sitting in the slip, no sails raised (though sometimes the jib is on the roller furler), and the boat will start shaking like an earthquake! It seems to be highly dependent on wind speed and even wind direction. I've done a little research online, and I think this might be "mast pumping", but it doesn't quite match the symptoms I've read elsewhere because it doesn't happen when I'm sailing, only when I'm in the slip.
Here are my symptoms:
Any idea what might be going on? Can you suggest possible fixes? Thanks! Please don't hesitate to ask for more info, I'm sure I've overlooked something that seems trivial but might be a vital clue.
Here are my symptoms:
- A couple years ago this started in the winter when all the sails were off, and I thought I narrowed it down to the forestay being too loose, so I tightened that up and it stopped except during very intense storms.
- The following summer when the jib was on the furler, no problem.
- This past winter with the sail off I had no problem.
- Now this spring, since the shrinkwrap came off, it's been doing it again.
- I thought I spotted the mast itself flexing fore-aft at one point, but it's really hard to pin down what's going on from outside the boat. It can be a violent and loud earthquake inside, but on deck you might not notice the tiny tremor.
- The vibration is almost entirely from the mast forward, you barely notice it when you're in the salon except for the noise coming from the V-berth.
- I re-tuned the rig (by hand, I have no tools, nor specs for what the tension is supposed to be). The mast appears to be perfectly in column, no pre-bend (I don't think my boat is meant to have any, but I have no idea). The vibration went away.
- I put the jib onto the furler, and it came back with a vengeance. It now happens in much lighter winds than it ever has before, and it seems to stop if the wind gets harder. I have a vague idea that it happens most when the wind is coming at an angle from astern (not directly astern).
Any idea what might be going on? Can you suggest possible fixes? Thanks! Please don't hesitate to ask for more info, I'm sure I've overlooked something that seems trivial but might be a vital clue.