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Old 21-05-2007, 18:57   #1
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Failed Shroud Deck Plate

So Sunday we failed the shroud deck plate. We didn't lose the mast and an inspection of the mast reveals no visible cracking.

I am on the tail of finding someone who may stock or sell original style plates but I am not holding my breath. I don't speak much Swedish and and sending emails in english in the blind on Swedish and Danish websites.

So, If the search turns up blank what are people's experiences and thoughts about making the plates.

The plates look pretty simple with two through bolts and a backing plate. On the inside there is an eye to attach the tie rod that goes down to the hull but this is a separate piece. I am planning however, to replace everything I can so I will likely be making the inside piece as well. We will also make the forestay fittings and backstay fittings if we can't find a source.

The only mildly tricky part is that the plate has a bit of a u-channel feature to it. The deck is also curved so we are probably looking at a compund curve and may need to have a mold and a press to make the plate. I am wondering how important this feature is to the structural integrity of the system.

Thoughts or advice is appreciated. Also interested to hear about material recommendations.
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Old 21-05-2007, 19:03   #2
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Quote:
shroud deck plate.
Deck plate...?

You mean a chain-plate?

Something that attaches the rigging wire to the hull..

I had my replacement chain plates made at a local machine shop...No big deal.
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Old 21-05-2007, 19:28   #3
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If the photo shows the plate, it is rail mounted and that is the U shape you are describing. Odd detail if that then attaches to a rod under the deck because the angle will be different (inward) so the load is not really transferred directly. I'm no rigger but it looks like you would be better off with an external plate (exterior of hull, down from rail) so you could spread out the load (can't be much of a backing plate) and attach directly to reinforcing you add inside the hull.
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Old 21-05-2007, 21:05   #4
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When I had a Pearson Renegade 27, I broke a chainplate in the area of a bolt hole when a crane dropped my boat into the water from a height of about five feet. The sling slid off the bow of my boat and there was a giant splash with instant destruction of one chainplate.

I then inspected all the other chainplates, and several of them had cracks in the stainless steel and were well on the way to failure. I was lucky to not lose my mast.

I fabricated all new chainplates for my boat using stainless steel flat bar. It wasn't that big of a deal making my own chainplates. I did use a drill press for making the holes. Polishing the chainplates to a bright smooth finish took as much time as actually making the chainplate.

Making chainplates isn't rocket science. Go for it.
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Old 21-05-2007, 21:13   #5
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Stainless Steel fittings....

I just had a mounting plate made up for under my fuel tank fillers. (PO had drilled too many holes in the deck.)

I found that machine shops don't weld, welders don't machine and neither stocks stainless.

My suggestion : Get your local Stainless Steel supplier to cut a piece to size, then take it to the machine shop and the welder, not necessarily in that order.

If you take the old fitting with you it will save much confusion.
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Old 21-05-2007, 21:20   #6
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In a since I have deck plates too but still called chainplates.
Mine come up thru the deck about 18" from the bulwark. Under the deck they attach to a structural bulkhead backed with SS plates and these bulkheads run directly to the bilge and are attached to the hull as part of the hull that actually meets the keel foundation.

In another words it's kind of a big circle going from the top of the mast, down the shroud, thru a bulkhead, thru the keel foundation and then back up again, The only thing that keeps the circle from elongating more is the strength of the deck and the stress rod (don't know the name of it) that attaches between the deck ring and the mast foot casting (keel stepped mast).

I would assume that your "tie rods" surves the same purpose as my bulkheads..........................._/)
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Old 21-05-2007, 21:44   #7
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Quote:
Originally Posted by Ex-Calif
So Sunday we failed the shroud deck plate. We didn't lose the mast and an inspection of the mast reveals no visible cracking.

I am on the tail of finding someone who may stock or sell original style plates but I am not holding my breath. I don't speak much Swedish and and sending emails in english in the blind on Swedish and Danish websites.

So, If the search turns up blank what are people's experiences and thoughts about making the plates.

The plates look pretty simple with two through bolts and a backing plate. On the inside there is an eye to attach the tie rod that goes down to the hull but this is a separate piece. I am planning however, to replace everything I can so I will likely be making the inside piece as well. We will also make the forestay fittings and backstay fittings if we can't find a source.

The only mildly tricky part is that the plate has a bit of a u-channel feature to it. The deck is also curved so we are probably looking at a compund curve and may need to have a mold and a press to make the plate. I am wondering how important this feature is to the structural integrity of the system.

Thoughts or advice is appreciated. Also interested to hear about material recommendations.
Yo Dan,

you were certainly very lucky you did not lose the rig! Although your photos show where this fitting is located, you need a closeup to show the chainplate detail. Still, from what I can see, this a custom-made fitting, perhaps too light for the job. You would be wise to hire an expert rigger to get new robust replacements made and installed.

best, andy
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Old 22-05-2007, 02:49   #8
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As andy suggested, close-up photos depicting the failure and the interior supporting structure (backing, tie rod & attachments) would help.

On the face of it, I’d be inclined to support Larry’s suggestion that you convert to exterior (thru-hull bolted) chainplates. The pictured design looks a little “gimpy”.

Delmarrey: You might consider adding an escutcheon (deck plate), to your chainplates for water-proofing.
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Old 22-05-2007, 06:45   #9
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Thanks for all the replies so far. It's been very helpful. Also appreciate the terminology correction.

I wasn't smart enough to get close up shot of the failure (the photo above is from the survey) but pretty much one leg of the the d-ring part just gave way and now looks like an upside down J. No deck failure, bolt failure or plate failure. If I had one it would be a 20 minute job.

It is a thru hull fitting. In my endless internet surfing I came up with some cross sections of the set up. Pictures below.

The first is the cross section at the deck. You can see based on the hull shape the pull is pretty much straight down to the 10mm hull.

The next is the hull fitting cross section. It is a through hull fitting as well. The next is a shot of the previously failed lower tie rod )Maxi's term) bracket.

Intrestingly I found a source for the tie rod and all the tie rod hardware but not the chain plate. Hmmm...

The last is a shot of the all new tie rod harware.

These drawings should make it pretty easy for my materials guy, machine shop guy and welder to make something up ;-)

The first cross section doesn't seem to accurately depict how much the
chain plate wraps on the deck "rail." I am thinking that the wrap takes up some of the lateral forces on the chain plate as the angle changes from the shroud to the tie rod. Without the wrap the lateral loading is on the fibreglass bolt holes. There are 4 of them.

What do you all think? Am I over analyzing this?

Any other advice appreciated.
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Old 22-05-2007, 13:25   #10
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Quote:
Originally Posted by GordMay
Delmarrey: You might consider adding an escutcheon (deck plate), to your chainplates for water-proofing.
They are in the works. I've had to replace the sealant every spring. I'm trying to come up with something that fits over the two without pulling the shrouds (an E-plate) and that will seal up the sides, a bit, of the vertical plates.

The underside is a 8" X 10" flanged to the deck weldment. I want to sandwitch the deck.

Sorry, didn't mean to steal the thread.
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Old 22-05-2007, 13:40   #11
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Quote:
Originally Posted by Ex-Calif
What do you all think? Am I over analyzing this?

Any other advice appreciated.
The part that bothers me is it's NOT a straight pull between the chain plate and the underlay work. That angle piece has a side stress affect rather then a straight pull. That would cause a twisting of the angle. It should be a clevis, straddling the center of effort.

That sideways working is probably what caused the first cracks and eventually failure.

Angles are designed for support work, not push/pulling. Maybe for a spring attachment??? I would definitely change the design. You could ask any building architect and he would tell you not to use angles for push/pull applications. That was doomed from the start!

I would attempt to get everything in a straight line and then I'd check out the other side of the boat. It's next!
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Old 22-05-2007, 14:09   #12
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It looks to me like they are using the deck as a sort of spreader and all the sideways load is carried by the bolt going through the coaming, with maybe a little bit going to the wrap-around deck plate. Doesn't look like a very good design to me. Replacing that setup with normal chainplates on the outside of the hull with maybe some extra glass reinforcement on the inside and backing plates would be your best option, IMHO. Another option would be to replace all that hardware inside the boat with one continuous chainplate that goes from the bottom angle through the coaming to the shroud turnbuckle, and the usual floating deck plate on top of the coaming. This would work the same as the original design, except that there would be more bearing surface to the deck for the sideways load. Seems to me that the boat builders were more concerned with appearance that structural integrity in this design.
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Old 22-05-2007, 14:12   #13
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Quote:
Originally Posted by delmarrey
The part that bothers me is it's NOT a straight pull between the chain plate and the underlay work. That angle piece has a side stress affect rather then a straight pull. That would cause a twisting of the angle Ö
That sideways working is probably what caused the first cracks and eventually failure.
Ö I would definitely change the design Ö
Ö I would attempt to get everything in a straight line and then I'd check out the other side of the boat. It's next!
Quote:
Originally Posted by capt lar
Ö Odd detail if that then attaches to a rod under the deck because the angle will be different (inward) so the load is not really transferred directly. I'm no rigger but it looks like you would be better off with an external plate (exterior of hull, down from rail) so you could spread out the load (can't be much of a backing plate) and attach directly to reinforcing you add inside the hull.
I donít see any good way to straighten the shroud to hull loading line (important, as noted above), without going to an outboard (exterior) chainplate Ė which would also be the simplest & cheapest solution.
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Old 22-05-2007, 14:32   #14
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You might consider building carbon fiber chain plates. They may work much better in your situation. Here are several links to sites with some examples.

Building Galene-Composite Chainplates

Floats

In the second link, scroll down to the short explanation of the chainplates and then click on the picture on the left to open a photo album.

Good luck
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Old 22-05-2007, 15:54   #15
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Thanks for all the inputs. I have received a reply back from someone I have been told my several sources is a "maxi expert" and he advises the chain plates are not stocked as spare parts by anyone and so they have to be made.

He doesn't advise a redesign of the system pointing out it's worked for 25 years. I don't know if I agree totally. This system is obviously under designed from a materials sizing standpoint and very susceptible to corrosion at some very key points. It also has significant stregth in some areas (5/16 inch shrouds, 1/4 inch steel tie rods) and reall weak features as well (side loading on several brackets and undersized rings). The failure point was where the ring attaches to the deck plate.

This spot was corroded and in my opinion under designed - probably 1/4 inch diameter. I am going to have chain plates and backing plates made with the same design but thicken up the ring, meaning a bigger contact/weld joint at the plate.

As far as the side loading, don't all designs have to transfer the lateral loading into the structure somehow? I am having a hard time visualizing and "external" chain plate but I am guessing it is attached to the side of the hull and the attach point for the shroud sticks up above the deckline?

I don't know if that much redesign is what I am after. Carbon fiber sounds interesting but again too much redesign effort.

So I will get the new plates made, a bit beefier, and send pics when it is done.

BTW - At least one person has told me not to use stainless but to use high alloy/high tensile steel.

Thoughts?
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