Pitted chainplate- replace now or later?

[Kelpie]

Hope the image links work.
I've just pulled the chainplate from one of my cap shrouds. Noticed some brown discolouration around the entry point in the deck, and upon further investigation the lower part looked quite bad with surface rust and black pitting. It was also slightly magnetic, unlike all of the other chainplates, which I thought might be a bad sign.

Anyway I've given it a quick clean up with a 120 flap disc. To my untrained eye the pitting is not too deep and there must be 99%+ of the original metal still there. Hard to see how this is a weak point compared to the 8mm diameter shroud itself. But I know that it doesn't always work like that and I'm a bit out of my depth on the finer points of metallurgy.

For context, I'm a long way from home and waiting in SE Ireland for a window to cross Biscay. So no pressure.
Local engineering firm can supply me a new length of bar but only in 304 grade.

Obviously it's very hard to tell from a photo just how bad the existing chainplate is, but an extra opinion never hurts, so I'd be grateful for any words of wisdom.

PXL-20210821-111309840
PXL-20210821-111304943
PXL-20210821-111259371
PXL-20210821-111253429
PXL-20210821-111248066

 

[cherod]

i believe 304 is actually stronger than 316 although will stain easier and less resistant to sea water . if it is slightly magnetic then it prob already is 304 .. a length of flat bar 316 should not be expensive , and get a few holes drilled in it if it gives you peace of mind,,,,, happy voyage .

 

[Kilo]

If you have time before heading off why not source the bar in 316, have it sent to the local machine shop for them to drill?
Alternatively get one made up in 304 for now, it'll see you safely wherever you're headed then replace with 316 at your leisure?
I was going to wade in with comments to the effect of don't listen to the worry monsters for whom the slightest pimple in a bit of chrome is reason for a complete refit.... But then I looked at the pics & those pits might be hiding a multitude of issues.
Was there some form of mixed metals corrosion going on?

 

[Kelpie]

The only mixing going on would have been different grades of stainless. I think the pitting is a sign of historic water ingress.

 

[Tranona]

Classic crevice corrosion from leaks around where the plate goes through the deck. If you seal it well 304 would be fine. However would be inclined to re-use it. Again well sealed to no further water gets in.

 

[webcraft]

It lookds pretty superficial compared to the thickness of the metal. See Tranona's comment above.

The chainplate is in tension, shouldn't be any bending or twising moments. I cannot see any way that could possibly fail in tension. As you say, the rigging is thinner.

Personally I would be happy to go with it, more than happy. As it seems so easy to replace, maybe get a set made at your leisure somewhere sometime then it will be one more thing to cross off the worry list. But not now, in a rush. If you try to get one made locally and it takes days or a week, you might miss a really good weather window and end up crossing Biscay in serious rig-testing weather! And it might well. Took me A YEAR to get a new bow roller/chainplate made locally forAvy-J. Don't believe anything anyone says in KQ or asnywhere else about a quick job!

What's that wafting on the breeze? It's the smell of tapas and sunshine!

- W

 

[ghostlymoron]

For critical components the correct material is 316 stainless these days (although galvanized was used before it was available so for peace of mind all items of lesser spec. should be replaced. That said, it is very unlikely to fail in the short term but that may not be very comforting when you're 60 miles offshore in an autumn gale.

 

[dehlerdave]

Visual inspection will not give you the correct assurance, cracks can start under these pits and proper Non Destructive Examination of the volume of the material is the only way to be sure. Probably quicker and cheaper to replace.

 

[Laminar Flow]

In general terms, the safety factors on chain plates are quite substantial and in the neighbourhood of somewhere around 3.

While the finish on your chainplates appears fairly rustic, I would suggest, that if it were me, to polish them up nicely, reinstall and keep an eye on them.

 

[Neeves]

Its your call - but you seem to imply you can get some 304 of the right size from a local engineering firm (and presumably they could drill it). If they have the bar and can drill is NOW! - go for it - it is surely not expensive. You have already removed the original, without drama - and you could have a replacement (in theory) by lunchtime tomorrow - how long will it take to replace (you have already pulled the original - so you anticipated replacement even if only the old one).

So, to me, it depends on timing and the credibility of the time defined by the engineering firm.

If you see a weather window developing quickly, go for that - but if there is nothing really enticing - it will give you something to do, or when you cross Biscay.

Jonathan

 

[Neeves]

I know this will seem like a very stupid question and has little to do with your thread.

But you are a long way from home in a 'foreign' land, about to undertake a challenging passage (though I hope it is not challenging, simply enjoyable) - what possessed you to remove a chain plate NOW!

Take care, stay safe

Jonathan

 

[Kelpie]

@Neeves
The engineer turned out not to have the correct size in stock, I'd have had to wait a few days, or go up a size and then deal with whatever problems that created. It doesn't help that it's the weekend and I was very lucky to be able to catch him at all.

Forecast looks pretty good over the next few days so I've reinstalled the chainplate with ample sealant and I'm quite happy to deal with it later.

As for why I pulled it... I suppose the impending Biscay crossing is making me more and more critical of the boat, and I'm not inclined to simply ignore things that might linger in the back of my mind.

The good news is that next time I pull the chainplate it will be much easier, and my confidence in the boat has gone up a few notches. Time well spent, IMHO.

 

[webcraft]

@Neeves
The engineer turned out not to have the correct size in stock, I'd have had to wait a few days, or go up a size and then deal with whatever problems that created. It doesn't help that it's the weekend and I was very lucky to be able to catch him at all.

Forecast looks pretty good over the next few days so I've reinstalled the chainplate with ample sealant and I'm quite happy to deal with it later.

As for why I pulled it... I suppose the impending Biscay crossing is making me more and more critical of the boat, and I'm not inclined to simply ignore things that might linger in the back of my mind.

The good news is that next time I pull the chainplate it will be much easier, and my confidence in the boat has gone up a few notches. Time well spent, IMHO.

Also, the last time I got an 'engineer' to make a chainplate I ended up putting the old one back because the 'engineer' had welded the threads onto the underside of the deckplate trathegr than making the thing out of a continuous piece of stainless. Getting new ones made is probably not something to do in a rush or when stressed,

And the good news is, our old chainplate made it across Biscay and is still holding up. Your chainplates are much more massive, and will probably survive until the heat death of the universe and beyond. I reckon you are good to go. Have you got the Navtex working?

Watching Marine Traffic and cheering you on here.


- W

 

[Kelpie]

I think the Navtex is working, although I maybe need to look at the list of stations as there is a lot of garbled stuff in there.
Forecast is looking really pretty good though, and even the stronger winds near A Coruna seem to have lessened.
See you on the other side...

 

[webcraft]

I think the Navtex is working, although I maybe need to look at the list of stations as there is a lot of garbled stuff in there.
Forecast is looking really pretty good though, and even the stronger winds near A Coruna seem to have lessened.
See you on the other side...

Is that you off? Can't see you on AIS right now.

Have a great trip, keep in touch. See you in Portugal soon.

- W

 

[Wansworth]

Pleanty of marine engineering in Vigo and materials

 

[Kelpie]

Is that you off? Can't see you on AIS right now.

Have a great trip, keep in touch. See you in Portugal soon.

- W

Not away quite yet- haven't paid the harbour so will have to wait until they open the office in the morning ?. Breakfast then away, need a bit of tide under us to get out of here and HW is around 7am so best not hang about too long.

 

[webcraft]

Not away quite yet- haven't paid the harbour so will have to wait until they open the office in the morning ?. Breakfast then away, need a bit of tide under us to get out of here and HW is around 7am so best not hang about too long.

Bon Voyage, next time we communicate in a few days you will be in La Coruna and we hope to be in the Western Isles.

- W

 

[Wansworth]

Hope you have your su cream and Panama ready,warm here in Galicia,safe voyage

 

[Wansworth]

If you do go to Vigo for your shroud plate better enter into the Fish dock pass Davila marina and right at the end is a yacht club.All around that area are ship builders steel suppliers and chandlers,bars and supermarkets anda bus into Vigo.