mast shake?

[Megunticook]

Just finished a delightful 2-week jaunt in Penobscot Bay, excellent weather and plenty of strong breezes but nothing over the top. Fourth summer with the CD and she never disappoints, always teaching me more about boats, wind, water.

So one thing I noticed this year is when a strong gust pushed me over at 25-35 degrees (usually just for a short spell, if not I spill a little wind off the main to stand her up a little taller and regain her footing), while close hauled with a reefed main and working jib, I'd glance up at the windex and it's shaking madly. It doesn't seem like the mast itself is shaking, although it might be vibrating enough to induce a shake in the windex, which is bolted on tightly to the top of the mast crane. I never see the windex shake like that unless the mast is laying way over. Is this normal? Possible I don't have my rigging tightened down enough and it's allowing the mast to vibrate more than it should? Or is this just the normal abuse that 20+ knots of wind will cause?

Just curious if anyone's observed this on their boat. I tuned my own rig this year, intentionally erring a bit on the side of too loose (rigging was new two summers ago), but the forestay is tight. I find the fractional rig challenging--you tighten the backstay too much, the mast curves back hard and the upper shrouds slacken. Tighten them and the backstay feels slack. I try to get the mast just slightly bent and all the wire tight but still a little flexible with a modest push of the hand.

[Jim Walsh]

I've never owned a Typhoon but I've never noticed my Windex shaking in a gust on any boat I've owned. As an aside, loose standing rigging is never a good thing. I'm sure one of the many Typhoon owners will chime in with rigging tension advice.

[Carl Thunberg]

Sorry, I was distracted by the two weeks on a Typhoon. How did that go? I spent a couple weeks on my former CD25, and that was enough to get me to buy a bigger boat (CD30).

I have no idea what could be causing your Windex to shake, other than vortex shedding, which is what brought the Tacoma Narrows Bridge down. Harmonics are a hard thing to predict.

[pete faga]

Borrow a loose gauge and tune the rigging and see if that helps.
There might be a user guide for you to visit on our web site for rigging tuning

Then you have to duplicate the wind scenerio
Pete

[tartansailor]

You are using a Loose Gauge, Are you not?
Uppers, then lowers, then uppers, lowers, etc, etc.
Tighten to wire size recommendations first,
only then you can back off slightly.
It is good to have a very slight bend in your mast,
and rake of about 1 to 2 inches.
Hope I'm not repeating the obvious.
Good Luck.
Dick

[Megunticook]

We didn't sleep aboard the boat--stayed on an island and did day sailing around the bay. But it's fine to sleep on. A week might be a bit much.

I decided to order a Loos gauge, the PT-1 was only $85 shipped. I'm guessing my rigging is a tad loose--from what I can tell, that's better than too tight, unless you accidentally jibe and shock load your wires.

Will be curious when the gauge comes to find how far off I am. Guessing the forestay is close, others may be a tad loose.

[mgphl52]

Will be curious when the gauge comes to find how far off I am. Guessing the forestay is close, others may be a tad loose.

Make sure you maintain a bit of aft rake. You should make small adjustments both fore and aft stay, but only after insuring the mast is "in column" and the shrouds are at proper tension.

[tjr818]

i have to throw a quote from the manual in here:

UNDER NO CIRCUMSTANCES TAKE UP THE RIGGING TO BAR TIGHT TENSIONS.

And note that that sentence is in all caps in the manual.

[Jim Walsh]

i have to throw a quote from the manual in here:

UNDER NO CIRCUMSTANCES TAKE UP THE RIGGING TO BAR TIGHT TENSIONS.

And note that that sentence is in all caps in the manual.

Precisely why the use of the Loos gage is a good idea as it provides objective evidence of your desired tension. Subjective guidelines are troublesome as no two peoples peceptions are alike.

[sgbernd]

I would suspect that as you heeled her over, the airflow was disturbed and the Windex at the top of the mast which is usually in clean air found itself in turbulent flow. Thus the wind was flowing up the mast over the Windex vertically rather than horizontally. I have had the mast shake while anchored in >32kts and it is a low frequency vibration which you can feel thru the boat especially if you put your hand on the mast. What you describe doesn't sound like mast vibration.

If it is turbulent flow, there is no cause for concern. Just ease the main or reef to straighten her up. If the mast is shaking, it doesn't really hurt anything but you might check the tension as others have recommended.

s.g.bernd

[Megunticook]

That sounds right to me--when the mast is angled from the boat heeling, at some point the wind angle is blowing up at the bottom of the windex as much as the side, and it's probably not designed for that--plus the turbulence issue you mentioned.

Loos gauge was shipped today--will be curious to see the results. I'll feel better when everything's adjusted.

[Megunticook]

The loos gauge arrived last night, so got out to the boat at the end of the day today to tune the rigging.

Forestay was at 10% breaking strength, I tightened it to 15% as per Loos recommendation.

Upper shrouds were less than 10%, tightened those to 15% as well.

Didn't have time to do the lower shrouds or backstay--next time. Lower shrouds were at roughly 10%, backstay was well below that.

Is the backstay generally looser than the rest of the rigging? Seems like it would need to be, especially on a fractional rig like mine, or else it will really exaggerate the mast bend. The swept back upper shrouds seem to provide most of the balance against the forestay.

I'm glad I'm doing this! Will be interesting to sail her once I'm done and see how things behave.

[Ben Miller]

Keep us posted! I'm curious to hear how you wind up setting up your rigging. I've been following various guides for rig set up, but don't have a Loos gauge, so it's just trial and error for me.

[Megunticook]

Finished tuning the rig yesterday. I definitely find the fractional rig tricky, and the guidance online is all over the map. I had a professional rigger show me when I replaced the rig a few years back, and he had it cranked down pretty hard, but the wire was new and he said it would stretch some the first year (he didn't use a gauge, just did it by feel).

I did the lower shrouds to about 17% of breaking strength, which helped straighten out the mast from the curve induced by the upper shrouds pushing on the swept back spreaders. I tightened the backstay to only about 7%, wanted to do more but it seemed like it was just creating too much of a curve at the top part of the mast (and I keep reading that the forestay is counterbalanced by the upper shrouds in a fractional rig more than the backstay). Everything but the backstay feels very tight, but you can still pull on it with your hand and move it an inch or so, which is what the CD manual recommends.

Final tensions:
forestay 18%
backstay 7%
upper shrouds 15%
lower shrouds 17%

I'll go sailing with it like that and see how it does. Curious to see if the leeward shrouds go slack at all.

Seems like rig tuning is less a science and more of an art, with lots of factors playing into it. On mine I just want to be sure I'm in the range where I'm not risking unecessary stress on anything by being too loose or too tight. The gauge definitely helps--the Loos guidelines say never exceed 25% breaking strength, and I'm well under that, so that gives me peace of mind.

Now if I can only sneak off for a couple hours of sailing this weekend. . .