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Bow chainplate blowout

Posted By: BayMaven

Bow chainplate blowout - 07/13/14 07:29 PM

Has anyone had to deal with this?

[img]https://plus.google.com/u/0/photos?pid=6030345076995377378&oid=100427919838747153607[/img]

The boat is an old nacra 5.2 which is a blast to sail in big wind. Unfortunately, big wind + big boy on wire = plate blowout. No wire breakage was evident and the rig and sails were recovered with a small puncture wound in the jib from the flying plate.

Also - has anyone ever upgraded to a lighter mast? ...was it worth the trouble and expense?
Posted By: bacho

Re: Bow chainplate blowout - 07/14/14 02:46 AM

Your link doesn't seem to work for me. Maybe the pictures are not public?
Posted By: northsea junkie

Re: Bow chainplate blowout - 07/14/14 09:29 AM

The photo shows that the shroud-pin plus its internal plate has completely broken out the hull.

All can be repaired with a thick layer of glass laminate on the inside and combined with some glass on the outside. Only problem is to get access to the inside of the hull at that particular place.

Why are you pondering about a lighter mast after this experience in big wind?
Posted By: Hullflyer1

Re: Bow chainplate blowout - 07/14/14 10:24 AM

Is it he shroud attachment or the bridal wire attachment
Posted By: DennisMe

Re: Bow chainplate blowout - 07/14/14 10:42 AM

I have a Nacra 5.2. Its the Bridle wire attachment point. The shrouds on that boat attach right by the dagger boards.

Lots to upgrade on that boat but a lighter mast wouldn't be on my list unless someone had a nice one piece carbon mast for free...

I'm with Northsea Junky (who needs a shorter nick; "Diehard" would be an option ;-)

You can lift the lids off the bows with a strong putty knife and a chisel, just work a round methodically and 'feel your way' in order to not damage the hulls or lids (or your hands for that matter!).
Posted By: northsea junkie

Re: Bow chainplate blowout - 07/14/14 01:58 PM

Originally Posted by DennisMe


I'm with Northsea Junky (who needs a shorter nick; "Diehard" would be an option ;-)




Thanks Dennis, for your support, but I'm really no "Die-hard".

I know it maybe seems that way in the eye of some spectators, but it's all against my will.

I'm driven by my sigh to the Northsea, which put me sometimes in unexpected harsh conditions. But by this junkie behaviour I damage my 68 year old body severly. Somehow I'm compelled to do so.

Yes I know, just like in the movie with Bruce Willis.
Posted By: catman

Re: Bow chainplate blowout - 07/14/14 03:06 PM

Originally Posted by BayMaven
Has anyone had to deal with this?

[img]https://plus.google.com/u/0/photos?pid=6030345076995377378&oid=100427919838747153607[/img]

The boat is an old nacra 5.2 which is a blast to sail in big wind. Unfortunately, big wind + big boy on wire = plate blowout. No wire breakage was evident and the rig and sails were recovered with a small puncture wound in the jib from the flying plate.

Also - has anyone ever upgraded to a lighter mast? ...was it worth the trouble and expense?


Not hard to repair but it will require a bit of knowledge and time. You have to take the decks off at least part way. I say decks because you will have to repair the other side before it pulls out too. You have to change the way that tang is installed and supported especially since the hull is ripped out at that spot. Check your PM.
Posted By: catandahalf

Re: Bow chainplate blowout - 07/14/14 06:18 PM

Is the boat an older model without a core, or is it one of "Catalina's" foam core editions? What is the hull number? Whether it is cored or not-cored makes a final difference, because you are not faced with just lamination; core replacement will require a more lengthy and detailed retro.

Remove the entire deck because if you don't they become a pain to seal properly. Be careful as those deck plates are very rare.

As a former NACRA dealer, I wish you the best,

Bert Rice
Nacra 5.2 and 5.5 SL (retired)
Posted By: BayMaven

Re: Bow chainplate blowout - 07/18/14 03:55 AM

Thanks for the comments. The google plus image is public ... not sure how to paste actual photo here - html is disabled.

"The blowout" is the port bow forward chainplate - bridle tang - which blew completely through the fiberglass. Amazingly, the deck is still intact with no obvious cracks. I'll check, but as best I can tell this is a 1980 5.2 no core. I agree that any chainplate upgrade needs to be performed on both hulls. They are not robust enough for my taste. Now I'm worried the shroud chainplates might be suspect.

I'm fairly comfortable handling epoxy and glass - I brought these hulls back from their weedy resting place in VA Beach and re-glued deck delam as well as sand/fair/awlgrip both hulls. Fixing her is only economical as a DIY project.

Here is a pic of better days... [img]https://plus.google.com/u/0/photos/...4544068818&oid=100427919838747153607[/img]

As for carbon ... I've already concluded that would be insane ...ly expensive.

Sail Fast!
Posted By: JeffS

Re: Bow chainplate blowout - 07/18/14 12:12 PM

To post pics they need to be small size, click on "Switch to Fully Reply screen" button at bottom of the reply screen
click on "File Manager" button, click on "Browse" this enables you to find the file on your computer, find what you want click on it, once happy click on "Add File" click on "Done adding files" then it's done
Posted By: jollyrodgers

Re: Bow chainplate blowout - 07/18/14 08:20 PM

[Linked Image]
You had the BB code there. The problem was that you had linked to the entire collection.

You can buy a yard of carbon online for $25-40 and that should be enough for your repair. Carbon and epoxy is the way to go for strong repairs if racing rules are not a problem.
Posted By: catandahalf

Re: Bow chainplate blowout - 07/18/14 11:05 PM

Lighter and stronger - good advice from Maui!
Posted By: BayMaven

Re: Bow chainplate blowout - 10/27/14 01:04 AM

I have started the repair. Progress is documented on google+ ... https://plus.google.com/u/0/photos/100427919838747153607/albums/6030345077259053265

Finishing up is dependent on weather and available time. And how strongly the urge to fix the white topcoat is. However, sailing down in FL this winter is a motivator.
Posted By: northsea junkie

Re: Bow chainplate blowout - 10/27/14 08:18 AM

I can see you do it carefully.

Is this the original position of the plate in the hull?
Posted By: catman

Re: Bow chainplate blowout - 10/27/14 03:30 PM

Originally Posted by BayMaven
I have started the repair. Progress is documented on google+ ... https://plus.google.com/u/0/photos/100427919838747153607/albums/6030345077259053265

Finishing up is dependent on weather and available time. And how strongly the urge to fix the white topcoat is. However, sailing down in FL this winter is a motivator.


Looking good.

I would make sure that plate is at least 3/16" thick. You could also remove a little more of the forward sealing surface of the hull if you think it would help with room to work in there. Before you glass that plate make sure you add some glass to the inner hull where that plate will rest. I realize the torn hull will be beefed up but the other hull should be beefed up also. The most important thing is to get good adhesion. Sand well and pre wet the areas with epoxy before adding parts or glass. When you get ready to put that tang in bed it in a blob of epoxy putty to prevent any voids. Mix mill fiber in to that putty so it's strong. If you have any questions you want to discuss feel free to call me.

You can just brush some gelcoat over the repair area and do the fine finish later. You should cover the epoxy to protect it from the UV.
Posted By: Rolf_Nilsen

Re: Bow chainplate blowout - 10/27/14 03:40 PM

We did it like this to align the forces pulling on the chainplate and spread them to the hull.

Plywood was reinforced with glass on both sides.
Steel was cleaned and sanded, them glued to the plywood with thickened epoxy.
A couple of layers of glass on top again so the steel is properly sandwiched.
Then the bulkhead was installed in the hull and fixed with thickened epoxy and glass tape.

[Linked Image]

Guy in the pic liked the idea. Phill Brander was the one who came up with the idea and layup.

With the setup you are working on I would worry about lifting off the deck as it looks like there will be some leverage working there?
Posted By: Anonymous

Re: Bow chainplate blowout - 10/27/14 11:59 PM

With all due respect to you, Phill and a whole lot of other people who have done similar (which includes most wooden Taipans) that detail is ****. Epoxy won't stick long term to ali or stainless. This is not just an opinion it is fact. My boat was built with a similar detail by arguably the best wooden Taipan boat builder in the classes history and just before I bought it one of the chain plates pulled out. The boat was then taken by the previous owner to another experienced boat builder who "fixed" it using a similar detail and 3 years later I got a call from my club to say the mast had fallen down over night because a chainplate had pulled out. My chainplates are now bolted into the boat. Rolf in your photo a couple of small stainless angles bolted or welded to the chain plate and then through the frame would be literally 100 times stronger. The traditional way to detail that fitting would be to twist the legs after it had passed through the hull skin then through bolt them to each other through the frame.
Posted By: Rolf_Nilsen

Re: Bow chainplate blowout - 10/28/14 06:44 AM

Interesting!

The plate was drilled so there are lots of holes there and thickened epoxy used to build fillets before glassing over fills these holes. This would increase surface area and give improved mechanical strength. Comparable to embedding a bolt in epoxy.
Would this change your opinion or is this also done in the "standard but bad" way you mentioned?



For the chainplates we went for carbon chainplates glued to the hull. Stainless was to hard to work with.
Posted By: Pirate

Re: Bow chainplate blowout - 10/28/14 09:48 AM

There's pros and cons for both methods, the physical fixing of the chainplate with a bolt through the frame will eventually cause issues in the long term..... The timber frame WILL eventually shrink somewhat and the bolting then becomes loose which allows the chainplate to move ever so slightly, once that movement has been achieved it will slowly work against everything else that's retaining it in place.

The timber frame is a great way to spread the load over a greater area, this reduces the strength required in a specific area such as the original posters fitting would have required in the small area it used as the fixing point.


I guess the question is really one of time..........

Just how many years should we expect to get from setup A versus setup B ????

The OP's boat was probably designed with a "life expectancy" of X amount years of service, anything after that is probably a bonus or a headache ...... depending on how much work it requires in order to keep it going
wink
Posted By: Jake

Re: Bow chainplate blowout - 10/28/14 11:32 AM

Fiberglass and stainless will have different expansion rates in different temperatures so anything that just "pins" it in place (epoxy through holes, etc.) will likely fail over time. Bolts aren't the answer either because they can create very high compression stress on very small surface areas of fiberglass leading to cracking and failure. Wood is nice too, but, as someone pointed out, it suffers from the same same high compression loading from bolts and will compress over time.

Nacra catamarans built around the 90's (and I presume still today) use a method on the side stay chainplates where the chainplate is T-shaped with holes in the "T" section. Those holes holes are filled with long strand fiberglass roving. That plate and roving is glued in place and the roving is fanned out on the hull. Even if you get some mild separation of the steel and fiberglass, the roving that is woven through holes in the stainless will keep it in place. A Nacra 20 is shown below (and granted, this could have been made to look a lot prettier on the inside).

I whacked this boat so hard that the chainplate got a little loose. I built a pressurized cap and pushed some epoxy around the chainplate from the outside and firmed it back up.

[Linked Image]
[Linked Image]

I used a similar method to make a carbon fiber beam strap for a custom built A-cat that was starting to crack around where the rear beam connected to the hulls. Once the carbon roving entered the hull, I wet it out and fanned it out on the inside of the hulls.

[Linked Image]

[Linked Image]

You'll also notice the Orange N20 fenced in the backyard. That's "The General" and that dog was so mean it had to stay chained up.
Posted By: Rolf_Nilsen

Re: Bow chainplate blowout - 10/28/14 12:40 PM

It is 10degC in summer, and winter, here Jake, so no danger of different exansion ratios wink (at least it feels that way now)


Next time we will do carbon or machine a stainless bolt for this.


Very good thread this one!
Posted By: waterbug_wpb

Re: Bow chainplate blowout - 10/28/14 01:28 PM

+1 on Jake's solution.

I visited the Stilletto yard and they were doing an extensive retrofit of a 28 footer. I peeked in the hull near the main chainplate, and they had the same sort of deal going with the metal plate and carbon / kevlar roving (or webbing) put through the holes in the plate, and then fanned out and laminated to the hull at various lengths along what I presumed to be the load path(s).

The whole assembly was then sandwiched in another few layers of glass against the bracket and hull.

I would presume you need to be careful to avoid sharp edges/corners in the bracket to avoid chafe should that thing ever jiggle with expansion or cyclic loading?

Posted By: BayMaven

Re: Bow chainplate blowout - 10/28/14 01:43 PM

The port bow chain plate - or bridle bow tang if you will - blew out of the hull. The starboard tang held, but started to crack or shear off. Interestingly, neither the deck nor the hull showed any sign of twisting or raking. I was concerned when I refinished the hulls about the top/bottom seams of the two hulls halves, but they seem to be holding up well after ~30 years!

The shroud chain plates seem to be OK, but an inspection is warranted. Bolstering the glass under the shroud plates and through bolting are probably as far as I will go.

However, the discussion is interesting. Keeping old plastic boats alive may go against nature. This old nacra was rescued from my Dad's backyard where it deteriorated for 15+ years. The hull gel coat was pocked and the deck delaminating in spots and the rudders previously stolen. The fact that it even sailed again was due to a couple of key points:

1) A chat I had with an enthusiastic West River, MD cat sailor who used to deal nacra. His opinion was the 5.2 was built like a brick **** house and I should definitely rebuild the boat and race with them on weeknights!
2) My own (mad?) determination to put it right again.

RE point 2: It's not like I'm hurting for a ride. I have an Olson 34 keelboat and a Catalina 16.5 dinghy as well. It's just that the nacra 5.2 is so damn fun and scary in a breeze. Otherwise it is a pain in the butt to setup and launch.

I guess I'll see how my repairs hold up and hopefully have fun until she breaks again.
Posted By: catman

Re: Bow chainplate blowout - 10/28/14 05:26 PM

I would never use wood. In this case the tang will be bolted to the plate. A glass/foam bulkhead wouldn't hurt. One that encompassed the top third of the hull would be nice. I think the plate will work fine as long as it's strong, care is taken to get max adhesion and it gets time to cure properly.

This boat has an advantage when it comes to repair or the question of is it worth repairing. It does not have a core.



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