Failed Shroud Deck Plate

[Thermal]

Originally Posted by Ex-Calif

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?

This is true, but the chainplates are usually attached to some sort of bulkhead or reinforced area of the hull, that way the side load is spread out over a much larger portion of the hull.
Refabricating the failed piece is of course feasible, but you have to have confidence in the skill of the welder since all of the shroud tension is going through the weld, and the weld is also the first place corrosion will start.

[delmarrey]

Just to add more info to the discussion.

If one attaches chain plates to the side of the hull, it'll need to be a solid glass hull. A cored hull, the holes will elongate without some extra work to the hull.

If it were mine and wanted to put bolts thru the hull I would have backing plates secured to the hull and/or carbon-fiber/Kevlar laminated to the hull to strenghten the thru holes.

You were lucky to get 25 years out of that design. Mine have been in place for 26 years. I do an inspection on mine at least once before the first sail of the year.

BTW some of the smaller trailerable sail boats the chain plates are only secured to the deck.

Gord, you are right! A clevis would not be the cheapest. I keep forgetting we're not all Machinists with the tooling.

[Terra Nova]

Originally Posted by Ex-Calif

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.

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

Thoughts?

Yo Ex,

at least one person has suggested having a professional do this. This is just not an area for a do-it-yourself experiment.

best, andy

[Ex-Calif]

"at least one person has suggested having a professional do this. This is just not an area for a do-it-yourself experiment."

Thanks for the tip. Actually any change to the existing design is an experiment I would say. Don't worry I don't plan on welding these up myself although in my hands on days I was a decent welder certified in oxy acetylene and TIG.

Actually, there has been several bits of conflicting advice. From external chain plates to carbon fiber ones. As an engineer with 25 years experience it would be dumb of me not to ask questions and get some opinions.

There have been a lot of opinions for which I am very grateful. At the end of the day, I have to take all the inputs and make the decision myself.

The failure point is clearly the ring that is welded to the chain plate. Corrosion was a significant factor. The deck and hull are in perfect shape. No signes of stress or cracking. If I have a new chain plate built with a thicker ring and get 30 years out of it, that'll do me ;-)

Delmarrey & Thermal - Regarding the hull strength take another look at the cross section drawing. The rail is solid and is about 1 inch thick. There are 4 through bolts and a backing plate. I could extend the backing plate or improve the connection to the deck but in reality I probably want that fitting to fail before the deck lifts off the boat...

Thanks again for all the great input. I called my mechanic and he is started on the new plates. I told him to upsize the rings one size and let me see the pieces before welding.

[delmarrey]

I think the real culprit was the fact that the lower bracket was sealed in glass and from the air. Lack of air is one of SS worst enemy. Add a little water and it's off and running. You may want to keep it exposed to keep an eye on it. Have you check for cracks in the upper bracket?

As far as the upper bracket, making it any bigger wouldn't make any difference IMO. It would be nice if it were a "T" rather then an "L". It would give it more surface area against the under side of the deck.

I'll bet everyone now is running out to check their own chain plates!

[GordMay]

Chainplate Scantlings:
This table, from ”Skene’s Elements of Yacht Design” is a handy reference for sizing chainplates and tangs:
Goto:
http://www.cruisersforum.com/gallery...1325&catid=500

[Ex-Calif]

That is a very handy reference. Thanks!

I am hoping we end up with something as nice as this.

[capt lar]

[capt lar]

Hey ! My PhotoBucket talents are improving !
Above is a photo of the config on my Bristol. To get the extra berth, same condition with change of angle. Note the transfer of loads down, but inward. The hardware is heavy and no sign of cracks, but it is a spot to watch. Most common issue is leaks where passes through deck since it is not a straight pull.

[mike d.]

i would agree with Gord May. and move the plates through bolted to the outside. if your plates/half round rods are located at or near the toe rail, and your hull is not cored that is what i would do. all you would have to do for the shroud and stay angles is bent the upper part of the plate to match the shroud/stay angle, through bolt to the hull sides and you are done. this also allows you to keep an eye on every part of your plates and bolts to a lesser degree. any rust stains and you know you have to get to work. from the pics from what i can see they should have been attended to some time ago. i see alot of rust stains on the glass surrounding to hole in tohe deck.

[delmarrey]

Here's a sample of strong inboard chanplates secured with 1/2" bolts.

[Ex-Calif]

New chain plates are installed and we are back in business. I will post photos next week for anyone interested. Went a size up on the plate and the u-bolts and it is "much" beefier loooking now.

Backstay brackets are being manufactured as we speak.

[Tuxie]

Sorry for reviving old thread but do you happen to have those promised photos? (:

I bought Maxi 77 which happens to be my first sailboat and when I bought it it had half a meter snow on top of it so didn't get to see the deck... Now that snow has melted I transported the boat to my home town I was able to inspect the boat better and found interesting surprise. The chain plates have been converted so that there's no connection to the hull anymore but rather somewhat bigger chain plates.. However they happen to be made of normal iron which has rusted almost completely through.. It seems to be have something like 3cm thick metal originally but now it's at most 1cm thick.

It would be interesting to see what's the original and designed setup for Maxi to restore that. Especially as another side of the deck around the chain plate seems to have fractures in the fiberglass meaning I'll have some fun fiberglass work to look forward to.