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Old 23-02-2020, 15:30   #1
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Stainless steel thickness for rigging eye extension

Hi all,

I’ve hit a small snag with my standing rigging replacement. The mechanically swaged eye fitting I am using on the rear stay does not fit in the slot at the top of the mast.

I think the simplest solution will be a pair of stainless steel plates either side of the eye to extend it out a few inches.

I was about to go and grab some stainless plate that “looked thick enough” when I realised there’s probably a good formula or rule of thumb for this one.

The rear stay is standard 1x19 10 mm, the mast is pretty conservative at 50 feet.

Does anyone know of a theory or calculation that will give me the required plate thickness?
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Old 23-02-2020, 15:37   #2
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Re: Stainless steel thickness for rigging eye extension

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..........

I was about to go and grab some stainless plate that “looked thick enough” when I realised there’s probably a good formula or rule of thumb for this one.

The rear stay is standard 1x19 10 mm, the mast is pretty conservative at 50 feet.

Does anyone know of a theory or calculation that will give me the required plate thickness?
Nope, but when I had to do similar i figured that if the cross sectional area was about the same, it would be OK....

Sooo... I doubled the surface area and added a bit more just to be safe and the rig hasn't fallen down yet.

No idea if this approach is right and proper though!
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Old 23-02-2020, 15:58   #3
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Re: Stainless steel thickness for rigging eye extension

Yes, there are rather simple computations for calculation the double shear resistance of the connector plates you want to use to solve your problem. Wotname’s approach probably is simplest. Figure out what cross-sectional area you have now at the mast head tang, or at the stern backstay chainplate - and this area (plate thickness) will work - as long as the SS you use has the same mechanical properties as the existing rigging components.
Is the mast down or are you going to be working with angel wings?
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Old 23-02-2020, 16:27   #4
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Re: Stainless steel thickness for rigging eye extension

Well, the chain plate is half inch, some kind of weird steel that isn’t stainless but isn’t mild steel either. Based on that, two 6 mm plates, either side of the eye should do.

I just checked the tangs on the Hamma turnbuckles, and they are only 5 mm, so that seems to be the lower limit, at least for stainless.

Wottie, I was going to use your approach, but given this stuff is right at the top of the mast I got a bit concerned about weight.

So, the next question is, does it have to be 316 or would other stainless types work ok?
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Old 23-02-2020, 16:28   #5
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Re: Stainless steel thickness for rigging eye extension

Oh, and yes, I’m doing this job with the mast standing. Rather wish I wasn’t, but at least I can fabricate this stuff at sea level and carry it up.
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Old 23-02-2020, 16:44   #6
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Re: Stainless steel thickness for rigging eye extension

Matt, the breaking strength of your wire is available in the mfg's spec sheet. There is little point in having your plates much stronger than the wire, so simply having enough cross sectional area in the plates, using the nominal strength values for whatever s/s you use, to somewhat exceed the wires strength should do ok.

I would not worry about the use of 304 in that application, for there is little opportunity to have trapped de-oxygenated water lurking about in that location, and 304 is usually marginally stronger than 316. Oh... a few ounces (oops, grams) of additional weight at the masthead ain't gonna bother your delicate little boat at all IMO. I'd polish out any nicks or scratches or other stress risers before installing, though!

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Old 23-02-2020, 17:40   #7
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Re: Stainless steel thickness for rigging eye extension

“Delicate little boat...”

Do I detect a hint of Aussie Irony creeping in Jim?

Anyway, I just got lucky. Got a lead on a local welder with an exceptionally well organised workshop. He had a perfect piece of 6mm x 50 mm bar 316 in his stockpile. Cut off what I needed for $20 and cautioned me that I was in for a long, slow job drilling it.

And I will be, because my drill press in is long term storage in another state.

Oh well... out with the cutting oil.
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Old 23-02-2020, 19:16   #8
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Re: Stainless steel thickness for rigging eye extension

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“Delicate little boat...”

Do I detect a hint of Aussie Irony creeping in Jim?

Anyway, I just got lucky. Got a lead on a local welder with an exceptionally well organised workshop. He had a perfect piece of 6mm x 50 mm bar 316 in his stockpile. Cut off what I needed for $20 and cautioned me that I was in for a long, slow job drilling it.

And I will be, because my drill press in is long term storage in another state.

Oh well... out with the cutting oil.
Sheesh, Matt, I'd guess that the pins are 5/8 inch, and you will need to drill 4 holes. That's asking a lot for hand held drilling IMO. Might be a time to pay someone with a drill press to step in. Besides, those holes should be pretty straight and round to load the pins correctly... and those qualities are hard to achieve with hand drilling.

I love spending your money, mate!

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Old 23-02-2020, 19:22   #9
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Re: Stainless steel thickness for rigging eye extension

if you generously round the corners of the plates, you’ll get rid of a not insignificant amount of grams aloft. Oz - not so much.
Stainless doesn’t grind well - and don’t grind before drilling. Drilling stainless is tough enough without introducing yet another heat source.
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Old 23-02-2020, 19:56   #10
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Re: Stainless steel thickness for rigging eye extension

All done.

Drilling was not fun, but I have good drill bits, good cutting oil and a lot of patience. Pretty happy with the result, good tight fit with the rigging pin.

Final result (with nicely rounded corners) added 956 grams, including the extra rigging pin, washer and cotter pin. Not great, but probably not a disaster.

I’ll see if Searig do an extended version of the eye pin for these sorts of challenges next time I replace the standing rigging.
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Old 23-02-2020, 20:02   #11
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Re: Stainless steel thickness for rigging eye extension

6-1/2 hrs to solve the problem - most excellent.
Must be from all the extra blood flow to the brain, having to stand on the bottom side of the world.
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Old 23-02-2020, 20:20   #12
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Re: Stainless steel thickness for rigging eye extension

Does nobody read anything anymore???

If you are doing ANY rigging on a sailboat and you do not have a copy of Brion Toss' Rigging Apprentice you are just pissing in the wind. It has distilled in it more than a thousand years of rigging history and knowledge. Nobody answering a question here has ALL the details they need about your boat's full situation to actually make a REAL recommendation.

Get the book, read it and understand it BEFORE you go chopping up your boat.

And YES the formulas you want ARE clearly spelled out in that book.

There are other ways to get this knowledge, but wading through mechanical engineering texts is probably beyond most sailors. If Toss' book is beyond you, then you need to be hiring someone who DOES understand it.

Sigh. My worthless windmill jousting for the day...
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Old 23-02-2020, 21:45   #13
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Re: Stainless steel thickness for rigging eye extension

Dude. Chill. Seriously
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Old 23-02-2020, 21:45   #14
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Re: Stainless steel thickness for rigging eye extension

billknny - you need a hug

or a beer


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Old 23-02-2020, 21:47   #15
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Re: Stainless steel thickness for rigging eye extension

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6-1/2 hrs to solve the problem - most excellent.
Must be from all the extra blood flow to the brain, having to stand on the bottom side of the world.


On the upside, being on the bottom of the planet makes it easier to get up the mast.
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