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xyzzy

Replacement shroud attachments

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I'm replacing my shrouds and I'm not sure if I should keep the original mast attachment scheme.  Currently the upper shroud terminals are swage eyes, 3/8" eyes on 3/16" wire.  The eyes on either side are through-bolted to each other.  The shank of the eye is bent to try to align it to the load.  That seems a bit sketchy to me and a good way to start some cracks on the outside of the bend.  There's no articulation in any direction.

My idea for replacement is to use a Ronstan RF348 tang, through-bolted to the mast, as the shroud attachment point.  RF348.jpg

It's got a 3/8" fixing hole, which would mean I could keep the though bolt the same size for the existing holes in the mast.  The clevis is 5/16", and there are 5/16" eyes for 3/16" wire.  There's no load rating for this tang that I can find.  But I would think that with a 5/16" clevis it should be designed for the loads that a 5/16" eye is designed for.  It should be easier to bend this tang to the proper angle than bending an eye fitting.  And it will have articulation in one axis to allow for changes in angle with mast bend.

This plan seem reasonable?

What the existing terminals look like:

upper.thumb.jpg.4f1c237ffaff3f782910e57b5ddf1919.jpgeyeclose.thumb.jpg.1009159e73b639664eecd5b52294851a.jpglowers.thumb.jpg.0aeec866f3e7b8a2d1cb582f27ad1fa2.jpg

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One word - toggles.

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9 minutes ago, SloopJonB said:

One word - toggles.

Do you mean place an eye-fork toggle between the tang and the swage eye for more articulation?  Or is there some other means of attaching the stay to the mast that I'm missing?  The only other options I see are trying to retrofit backing plates for stem-ball or T-ball fittings, and I don't really see that as all that much better than a though bolted tang.

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  Is that a mast for a Schock boat? They did that a lot. That R fitting will work, but not as well as a single thickness of SS, about 1/8" thick x 1 3/4" long, 3/8" hole one end, 5/16" hole the other, attaching to a marine eye. This gives you a fitting that can be bent to the exact angle needed, has plenty of bearing surface at contact points. Also - you need to ensure that the thru bolt is the proper length: it must have full diameter/non threaded section thru all parts. Threads must end before fitting starts.

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2 hours ago, xyzzy said:

Do you mean place an eye-fork toggle between the tang and the swage eye for more articulation? 

Yes - but I'm not a rigger so......

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No one puts toggle aloft. A tang is the right solution. Your shroud angle is likely 11º. Do a little math, find a local rigger, it will all be fine.

 

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Boat is a San Juan.

The RF348 is bent to about a 22° angle.  My plan was the bend them to match the angle of the eyes after I take the stick down to do the changeover.  They are made of two 1/16" plates, and so 1/8" at the mast.  Would the single 1/8" plate be better because it will be easier to bend?  I assume a single plate with a hole would need a fork terminal rather than an eye.

I haven't measured how thick the existing eyes are, but I'd guess more than 1/8", so I might have to cut some more threads on the existing bolt to get it tight.  Or replace the bolt, but I doubt I'll find one with the perfect shank length that doesn't have me cut some extra threads.

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   If you bend that ronstan fitting much it throws off the lengths of the two plates & the alignment of the clevis pin holes goes bad, and the pin gets off axis to the load. Which is why I recommend a single piece of material - changing the angle does not affect the geometry.

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I see what you mean.  My plan to bend them was to stack washers between the plates and then clamp that down tight on a 5/16" bolt where the clevis pin is.  Then put the flat part in a vice.  Hopefully that can clamp the two plates into position well enough that they expand/contract on either side of the bend instead of just shifting position.

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If you're prepared to bend those Ronstan fittings and attempt to keep the alignment then you might as well bend your new eyes in the same fashion as the boat was rigged originally... I TOTALLY get that it looks ghetto (or ratchet or whatever we're saying these days) but there have been a ton of boats rigged that way over the years and I believe as sketchy as it looks that it's a sound method.

Not to say it couldn't be improved... change to t-balls is the obvious choice... but this may be a situation where it's tempting to overthink it.

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T-swages have their own issues as well. The tangs shown earlier with fresh straight swages is the way to go.

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A 3/8" eye fitting is 5/16" thick, while the tang is just 1/8".  It'll surely be easier for me to bend the tangs without adding cracks than to bend eyes.  I've yet to measure the angle I need, but just from eye-balling it, I think it's closer to the 22° of the tangs than to the 0° of straight eyes.  So less bending too.

But I'll see what happens bending and expect that it might not go well.  Maybe get a spare tang in case I bust one.  Seems like another possible problem is the spot welds holding the two plates together could let go from the plates wanting to slide.

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Let me make sure I understand this. You have 3/16" wire with 3/8" clevis pin which work to hold your mast up, and now, you want to change it to an eye fitting that has a smaller 5/16" pin? 

The correct tangs are available; you just need to talk to a rigger to get them, but I know that Claude, formerly of Metal Mast Marine, and currently of DC Products can make exactly what you need at a very reasonable price. Best of luck. 

Bam Miller 

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Yep.  What could go wrong?

My understanding is that aircraft eyes for 3/16" wire should be able to supply 100% of the rated strength of the wire.  So I shouldn't be making it any weaker by moving from marine eyes to aircraft eyes.  Aircraft eyes for 7/32" wire also use a 5/16" clevis and are supposed to be stronger than the wire I've got now.

Switching to tangs will mean the eyes aren't bent and aren't being loaded off axis.  So, assuming the tangs are not a new limiting factor, if anything this should be stronger than what I've got now.

At least that's my theory so far.

I also found a single plate shroud tang at rigrite, K-363C, 1/8" thick with 5/16" pin hole.  Suppose to be good for up to 7/32" shrouds.  Perhaps that would have been better.   It also factored into my reasoning that if a 1/8" thick plate for a 5/16" clevis and a 3/8" bolt can support 7/32" wire, then an identically dimensioned Ronstan tang ought to be good enough for 3/16". 

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