Chain Plate Fabrication for Island Packet

[lovinlifebda]

Broke a chain plate on our IP40 (1995) - got a message back from Island Packet that they're on vacation for about 2 weeks and are wanting to get moving on getting them ordered and shipped to us here.

Anyone out there know where IP gets their chain plates fabricated?

Thanks to all.
Cheers,
Sharna

[Stumble]

Sharna,

How did you break it?

I would imagine a local machine shop that works in 316 stainless should be able to recreate it without much difficulty if you can give them the old one as a pattern. We have certainly done it with titanium chainplates.

[lovinlifebda]

Hi Greg,

Appreciated the reply. Sailing in light air; just dropped the main, headed to anchor for the night. We're liveaboards and because of the IP set up (all 3 welded to the horizontal plate embedded in the hull behind all the cabinetry/bulkhead) taking them all out isn't something we want to do. Snead Island Boatworks (Steve) has been a godsend and is happy to help the local yard with the installation/glassing once we get the new chainplates. Even gave us the contact (Derek Dudinsky at JTR Marine in Gulfport, Fl who offered to try for a 4 to 6 week once we sent all 8 chainplates to him and was fantastic to deal with). Can't say enough positive things about either of them and their offer of great service. But we're in Bermuda. We were looking for someone who already has the drawings for the 1995 IP40 on hand so we didn't have to remove everything until closer to the time - and didn't want to remove the mast as well. So it was more a question - I should have worded it differently - anyone know who Island Packet gets to do their fabrication of chainplates. They've always been happy to share that kind of info in the past. We're the 4th owner and IP changed their system in 2000 to include weep holes so that if someone didn't properly maintain the chainplates, or had loose rigging causing flexing, it wasn't going to cause the hidden corrosion. Hey, when it's done we'll really know our girl intimately!
Thanks again.
Cheers,
Sharna

[Hannah on 'Rita T']

Sharna, call Steve Hollis at Ocean Sails, 297-1008, he can find you someone to fabricate a stopgap. or, Bluestocking here on the forum is a wealth of knowledge. If you need anythign else, pm me, I'd be happy to help.

[Stumble]

Ouch, sounds like they were long past corroded through, and you guys just saw them actually fail.

Sharna,

If you can give me exact measurements of the parts, including hole patterns thickness, and dimensions, I mite have something in our catalog that is close enough that it wouldn't require drafting the parts. If we did have to draft a new ones, we can do it from the dimensions, or from the parts, but the dimensions you give us need to be very exacting. I haven't shipped to the Bahamas before, but our lead time to the US is generally around four weeks. With an additional week if we have to have the part drafted.

The upside is that because titanium is non-corrosive in the marine environment, and has a higher yield and tensile strength than 316 stainless, crevice corrosion issues just aren't a concern, ever.

[Cheechako]

wow, never would have expected a boat that "young" to break a chainplate...... even in a storm!

[Stumble]

Originally Posted by Cheechako

wow, never would have expected a boat that "young" to break a chainplate...... even in a storm!

The recomendation from the experts is to pull and x-ray inspect stainless chainplates every 10 years. A boat at 17 years without inspection thus is well past the recomended inspection interval. It is rare, but even younger boats have had problems. Crevice corrosion is an insidious process litterly eating away at stainless from the inside out.

A recent article from Brion Toss about stainless chainplates. The Worst Possible Chainplates - All At Sea - Southeast

[Cheechako]

yeah, I understand SS all too well. Still ...it seems premature to me... maybe builder error to start with. how many on this board have broken a chainplate on their 30 year old boat... much less 15.... robust designs endure... etc...

[Stumble]

I think the difference here is between "broken" where the piece has completely seperated, and "broken" where the piece has lost a significant amount of its designed strength.

Most chainplates are built to be massively stronger than the rigging loads really justify, not because builders really want to spend the extra money and weight on them, but because they are designed with a very significant corrosion allowance. This allows a chainplate to see service lives longer than the start of corrosion, or even after loosing a significant amount of its initial strength due to corrosion.

Basically if you make something twice as strong as it needs to be, the lifespan is increased significantly. Make it ten times stronger, well even if you loose 90% of the material it will still hold.

The problem with this is that if the corrosion creates an unequal stress riser in the part, or causes it to deform easily, the failure method becomes part specific, and can't really be engineered to. And when dealing with 316 stainless, under the worst possible situations it can take as little at 4.5 years for a crevice to penetrate 8mm plate.

For a more in depth look at the rate of CC take a look at http://www.nsc.co.jp/en/tech/report/pdf/n9911.pdf . It's a little thick on the engineering side, but the conclusions are reasonably accessible to non-engineers.

[Cheechako]

If I'm envisioning these right... they are a welded asembly? three tabs on one plate...? Relying on the deck for support.? Is that what it is? Welds are always the first to corrode... Unless done to aircraft standards....

[neilpride]

Is one of the worst designs for a chainplate in the case of Island Packet, i believe the Stainles Steel dont come from a good quality source and the design? any metal encapsulated in fiberglass , Huffff,

For the OP, are you considered to swicht to external plates?? easy to inspect , no crevice corrosion, easy to clean...

Here is another IP piece of chainplate.

[DeepFrz]

External chain plates certainly can fail from crevice corrosion.

[neilpride]

Originally Posted by DeepFrz

External chain plates certainly can fail from crevice corrosion.

True, but no doubt about how easy are to inspect or clean or dismantle.

[DeepFrz]

True, but no doubt about how easy are to inspect or clean or dismantle.

True. I suppose some of that depends on how the internal cabinetry is constructed, but at least they are not imbedded in fiberglass.

[neilpride]

Topsides are preety thick in Ips, the only problem i see to swicht to external plates is the caprail .

Here are some pics to show how is the cabinetry...