Fried My Backstay Tensioner? - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 10-14-2007
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Fried My Backstay Tensioner?

Our boat has a backstay tensioner. Well, it did, anyway. I may have killed it .

We were close hauled and I went to add backstay tension to flatten the main to try to get a couple more tenths of a knot or so out of her. Forgetting that anti-clockwise was tightening, I turned the wheel clockwise. After a few turns it just kind of "froze up." Now it still turns, when the mast isn't under load, but it turns real hard. Talked the PO about it, and he fears I may have galled the threads.

How did I do that just using it, you ask? Well... Our backstay tensioner is a wheel that turns a nut. The backstay is attached to a long screw. Turning the wheel moves the screw in/out of the assembly. I knew the thing needed lube. I simply forgot. I surmise that by turning the thing under all that load, it heated the threads and galled the nut and/or the screw.

When next we go back out to the boat I'll give it a good shot of Boe-Shield and see what happens. If that doesn't straighten it out, is it possible to run a tap through the nut, assuming it's the nut that's damaged, to rescue the unit, or is it likely dead?

Backstay adjusters ain't cheap, looks like. The two Harken's Compu Spec came up with for our boat, depending on the clevis pin size (which I don't know), the B500 and B502, list at $1300. *Ouch* This Wichard Backstay Rigging Adjuster - Wheel is similar to our current one, but the load specs are much lower than the one recommended by Harken. Still, that one's $500.

Jim

Last edited by SEMIJim; 10-14-2007 at 09:48 PM. Reason: Added pointer to similar device and Harken products
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Old 10-14-2007
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Galling damages the surface of the thread. Running a tap or die on the thread will remove the high spots and without being under strain it might work better. But you have not repaired the surface of the thread. Because of this damage you can have a weaker thread and you can have surface roughness that will cause galling under load the next time you use the adjuster. If you damaged it then it will never repair itself. Without seeing what you have I can't say one way or the other but it sounds like you have a problem and need to replace it. Just a long distance guess and nothing more.
All the best,
Robert Gainer
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Never design a boat that is weaker then the mast

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Old 10-14-2007
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Quote:
Originally Posted by Tartan34C View Post
Because of this damage you can have a weaker thread and you can have surface roughness that will cause galling under load the next time you use the adjuster. If you damaged it then it will never repair itself.
Yeah, that's what I pretty much expected to hear .

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Originally Posted by Tartan34C View Post
Without seeing what you have I can't say one way or the other
It's a pretty simple mechanism. As I wrote: Imagine a long screw hooked to the backstay. Screw is threaded thru the center of a wheel. Bottom of the screw has a rectangular block on it that is captured such that the screw can't turn. There's not much that can go wrong with it.

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Originally Posted by Tartan34C View Post
but it sounds like you have a problem and need to replace it. Just a long distance guess and nothing more.
I understand. And I suspect you're right . An expensive lesson in why not to forget or put off even simple maintenance.

I'll first try the lubrication. If that doesn't resolve the problem, next I'll find a competent machinist. If re-tapping/-threading won't make it usable and reliable again, maybe the machinist can fabricate new parts more cheaply than a whole new tensioner would cost. If not: Then we'll have to decide whether to bite the bullet and replace it, or just do w/o a backstay tensioner.

Thanks for your comments, Robert.

Jim
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Old 10-15-2007
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If this part was stainless on stainless, and you've galled the threads, it's pretty much pooched. You have actually transferred material from one part to the other - even if you can clean one part up, the other is reduced, and probably weakened, as RG said.

My guess is a replacement is required for reliablity.

Before you decide to go without, there are lots of other styles of backstay adjusters....
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If this part was stainless on stainless, and you've galled the threads, it's pretty much pooched.
By the condition of the screw, which, despite constant exposure to the elements, is not rusted, I'm guessing the screw and "nut" are stainless.

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Originally Posted by Faster View Post
My guess is a replacement is required for reliablity.
If it isn't going to be reliable, I don't want it on the boat.

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Before you decide to go without, there are lots of other styles of backstay adjusters....
Well, yes, but it would appear that, regardless of style, "mid-size boat" backstay adjusters are expensive. There's X amount of load. Whatever style it is has to bear that load. Designing and fabricating hardware to bear that load and, even more difficult, operate while under that load, results in expense. If you know of a product that will handle the load, can actually be operated under the load, and wouldn't cost an arm and a leg, I'm all eyes. Btw: We're absolutely, positively not interested in going to a split backstay.

The Admiral is currently of the opinion that if the current backstay adjuster cannot be salvaged, and relatively inexpensively, there'll be no backstay adjuster. As much as it pains me to actually downgrade the rigging, especially due to my screw-up, I'm prone to agree. This is getting out of hand. Enough is enough.

Thanks for your comments, Faster. Apologies for the negativity. I'm in rather a black mood this morning.

Jim

Last edited by SEMIJim; 10-15-2007 at 10:12 AM. Reason: Thanks and apologies.
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Old 10-18-2007
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Update #1

The backstay adjuster is a Ronstan RF718. Google comes up with bupkis for it. Ronstan's site likewise comes up with nothing. So I suspect this device is older than dirt. Maybe I'll try contacting Ronstan. Maybe they have an old-timer there that remembers this thing and even knows where some spare parts are stashed in some dusty corner .

I'll have pictures later (in case anybody's interested). It's too late for me to fool with editing them down to size right now.

I'm now 99-44/100% certain it's toast. Applied Boe-Shield liberally, then tried to work the thing back-and-forth. If anything: It got stiffer.

We'll see what things look like after it's off the boat in another couple weeks.

Found out, in additional discussions elsewhere, that stainless-on-stainless is a Very Bad Combination precisely because to the tendency to gall. Better is a combination of stainless and brass. (E.g.: Stainless screw and bronze nut, in this case.)

Jim

Last edited by SEMIJim; 10-18-2007 at 10:00 AM. Reason: Corrected brass/bronze mistake
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Jim,
You may have meant stainless and bronze. Brass is a weak metal and in this use the zinc will leach out leaving just copper. Bronze is the common choice in a marine application.
All the best,
Robert Gainer
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Study the history of naval architecture and move forward knowing what didnít work before.

Donít waste time making the same old mistakes but instead make new ones and to insure your place in history be sure the mistakes are big ones.

Never design a mast that is weaker then the boat
Never design a boat that is weaker then the mast

Never listen to someone describe why your project will not work unless they can show you the broken pieces of their own version.
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Jim,

If you can't find replacement parts, as opposed to "downgrading", let me know when you have it off the boat. I spent 10 years with a precision screw manufacturing company and I'm pretty certain we can get you up and going with a reliable repair for MUCH less than even the cheapy replacement.




Going where no man has gone before (according to my wife)
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Old 10-18-2007
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Quote:
Originally Posted by Tartan34C View Post
Jim,
You may have meant stainless and bronze. Brass is a weak metal and in this use the zinc will leach out leaving just copper. Bronze is the common choice in a marine application.
All the best,
Robert Gainer
Yeah. Neuron misfire. Thanks for the correction. (Corrected in the post.)

Jim
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Quote:
Originally Posted by Wannafish View Post
Jim,

If you can't find replacement parts, as opposed to "downgrading", let me know when you have it off the boat. I spent 10 years with a precision screw manufacturing company and I'm pretty certain we can get you up and going with a reliable repair for MUCH less than even the cheapy replacement.
Thanks for the offer, WF! I may just take you up on it .

Last race is this-coming Saturday. "Mast Removal Day" and "Winterization Part I" is a week from Sunday. Haul-out is the Saturday following, with "Winterization Part II" probably the next day. (I'm avoiding getting depressed by all this by regarding the entire process as Yet Another Adventure.)

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Going where no man has gone before (according to my wife)


Jim
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