toggle quoted messageShow quoted text
I tackled this problem yesterday, and it did not go as planned. My main mast is now pumping fore-and-aft in a wide range of wind speeds with the wind on the beam (I haven't been able to test any other wind directions yet). The top of the mast seems to stay still, and there is little to no motion at the lower spreaders; the pumping is centered near the upper spreaders.
Before starting, I reviewed advice from this list, the Selden guide, Brion Toss's Rigger's Apprentice, Ivar Dedekam's Illustrated Sail and Rig Tuning, and other online sources. I thought I had a vague idea of what I was doing. Unfortunately, every one of those guides assumes you're starting from a freshly-stepped mast, so I had to improvise to apply the procedure to tune mine in-place (I couldn't use the folding-rule method because the stays were already under an unknown load). Here's what I did:
- removed a slight forward tilt of the uppermost part of the main by tightening the backstay, which, as I suspected going in, was the loosest of all the stays -- the previous owner installed the radar on a Questus backstay mount. I will probably put the radar back in its traditional place when I next unstep the mast. I did not adjust the forestay.
- removed a slight lateral S curve
- tightened the starboard cap shroud
- the port intermediate shroud
- the starboard lowers
- I tightened all four lowers one turn just because they all seemed a bit looser than what was described on this list (they now make a sort of tone when hit with a wooden hammer handle, but they don't quite resonate)
- tightened mizzen starboard cap shroud one turn to correct slight bend to port
- tightened all four mizzen lowers one turn because they seemed loose
- loosened port mizzen backstay half a turn. I know the backstays are supposed to be fairly loose and the port was a bit tighter than the starboard one
The masts were now in column and looked just about perfect. When the pumping first became apparent (when the weather turned, of course), I added a turn to the main's forward lowers in an attempt to induce a minuscule pre-bend. There was no perceptible difference in the mast shape, but there may have been a minor difference in the amount of pumping.
Does anyone have experience with this problem? I'd greatly appreciate some advice on how to fix it! I'm almost desperate enough to try a non-Amel-familiar professional rigger.
Ryan and Kelly
SM 233 Iteration
Boston, MA, USA
On Wed, May 16, 2018 at 6:25 PM, sangaris@...
Yep, that's the booklet. Check out the "Folding Rule Method" of tensioning.
Sounds reasonable that the existing rig is loose due to stretch. That makes it pretty easy to tension back up - just count the turns you take on starboard and do the same number on port, assuming the mast is in column to begin with.
Craig SN68 Sangaris, Ft Pierce FL
, wrote :
Steve, thanks for the data, that's very helpful.
Craig, thank you also for your advice. That's a great rule of thumb. I have The Complete Rigger's Apprentice, which discusses rig tuning a bit, but not as much as I'd hoped before I bought it. I will definitely read the booklet you mentioned (which is perhaps this free PDF
I suspect the slight looseness in my rig is because the wire has stretched over time. It was quite tight when I bought the boat, and I think the boat hadn't been sailed much by the previous owner after he replaced the standing rigging.
SM 233 Iteration
Boston, MA, USA