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Old 20-08-2018, 04:36   #1
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Chainplate how bad ?

Hello,

While i was grinding around chain plate, i touched it and a little bit on the corner is gone.

Do i need replace it ?
Weld it ?
or its still good as is ?

i am worried that under pressure a crack might come from this place.

Boat : columbia 9.6 ( 32 ft~)
The metal is aluminium if i am not mistaken
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Old 20-08-2018, 10:03   #2
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Re: Chainplate how bad ?

The metal must be inox , if you are not filling sure about it replace it
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Old 20-08-2018, 10:18   #3
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Re: Chainplate how bad ?

I saw a few corroded chain plates online that are still holding and the small bit that is missing is nothing compared to them but I would like to be sure.

If there are much higher chance of stress crack developing there and if it would of been changed by professionals because of that.

PS My bad about saying its aluminium , it must be inox
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Old 20-08-2018, 14:55   #4
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Chainplate how bad ?

I dont really see a notch, but radius it out and polish it, then it wont be a stress riser, meaning a crack wont propagate from there.
OK now I do, just polish it out, blend it in and take out the scratches
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Old 21-08-2018, 08:47   #5
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Re: Chainplate how bad ?

Seems like you are imto a project already, so How old are they? Might be a good idea to replace anyway. Esp. If for a cap shroud. Check the bolts holding them as well. It should not be terribly expensive to get the local metal shop to make duplicates in that size.

Strong 316 inox really doesnt normally gouge or cut very easy if just dinged by a grinder.
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Old 21-08-2018, 08:58   #6
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Re: Chainplate how bad ?

The damage that will get you is hidden, below the deck. This rounded nick will not contribute that that since it is not in the same place.


Whether they are bad below deck is a separate question.
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Old 21-08-2018, 09:23   #7
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Re: Chainplate how bad ?

You can see the rust in the laminate. It needs to be pulled and replaced. Id not be at all surprised if you find a crevice corrosion crack in the plate where it goes through the laminate.

It looks like it was fully glassed in which I consider A Very Bad Idea. I would route out around it after you pull it and install the new one with a proper sealant.
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Old 21-08-2018, 13:55   #8
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Re: Chainplate how bad ?

I can only see a rounded nick slightly above the level of the centre of the eye. If that's what you are referring to then it is of no concern as it is not subject to the maximum stresses seen below the shroud attachment point and the chainplate is slightly overwidth relative to the eye. [Picture it taken to absurdity: as a chainplate increases in width, the extra material added carries less and less of the stress as it gets further outward from the eye.] You could (if you were truly anal) round off the upper part of that chainplate into a perfect semicircle centred on the eye without weakening it in any way.

Looks to me like you got lucky - don't do it again! Can't comment on condition of chainplate(s) or their attachment bolts below deck.
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Old 21-08-2018, 18:44   #9
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Re: Chainplate how bad ?

Rounded holes and radii don't tend to propagate cracks easily but I agree with Suijin. If that is rust we are seeing through the glass it needs to be investigated. Drill an inspection hole in the glass if you want to check for rust, otherwise pull the chainplate and start fresh with new ones correctly bedded in.
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Old 21-08-2018, 18:55   #10
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Re: Chainplate how bad ?

Quote:
Originally Posted by Suijin View Post
You can see the rust in the laminate. It needs to be pulled and replaced. I’d not be at all surprised if you find a crevice corrosion crack in the plate where it goes through the laminate.

It looks like it was fully glassed in which I consider A Very Bad Idea. I would route out around it after you pull it and install the new one with a proper sealant.
+!

Attached is 1. ) an x-ray of a single pinhead size hole in stainless steel. You can clearly see the corrosion inside the ss is thousands of times larger than the pin hole on the surface. 2.) a broken ss propeller shaft. does not look all that bad on the outside but looks like an Aero chocolate bar on the inside.

Your chainplate is done, get rid of it and don't glass in the next one. SS corrodes in the absence of oxygen.
Ret'd Certified Corrosion Analyst.
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Old 22-08-2018, 05:24   #11
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Re: Chainplate how bad ?

First a word about "inox", a little used term that in fact means "stainless steel", the name most are more familiar with. I couldn't agree more with those who say replace. This an old boat and sadly, the chainplates are glassed in. This is very bad as SS - which is wonderful when fully exposed to the air (and water) - does horribly when glassed in. When SS does deteriorate it does so in an anerobic environment (no oxygen).

All sailors would do well to examine all their SS to make sure it is exposed to air. In your case - particularly with some rust spotting - your glassed in plate simply cannot be trusted. A chainplate failure is a risk you simply cannot take.

If all your plates are glassed in, you must replace them. Yes a bit of work, but not that bad, and not that expensive. Your life and your boat depend on it.
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Old 22-08-2018, 13:05   #12
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Re: Chainplate how bad ?

Some interesting insight into that brown staining beneath the fibreglass - a good warning to all of us.

Why then do you think bedding in flexible sealer will not harm the stainless steel by oxygen starvation at deck level, while glassing in is considered harmful? What makes the difference?
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Old 22-08-2018, 13:08   #13
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Re: Chainplate how bad ?

Agree with all the above. The notch you made is insignificant. The brown staining within the fibreglass shows you need to replace it now.
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Old 22-08-2018, 14:14   #14
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Re: Chainplate how bad ?

Quote:
Originally Posted by NevisDog View Post
Some interesting insight into that brown staining beneath the fibreglass - a good warning to all of us.

Why then do you think bedding in flexible sealer will not harm the stainless steel by oxygen starvation at deck level, while glassing in is considered harmful? What makes the difference?
There isn't any difference, sealed is sealed. You could argue that the sealant may be more flexible and be worse, but it's not likely to be significant.

The sealant is to keep the salt out, the salt is an electrolyte if you will and is the real enemy

I replaced mine with grade 5 Titanium, if it's a nice boat and you want to keep it, price the Ti, it may not be nearly as expensive as you may think. The Ti is much stronger and will last longer than the boat will.
however I have seen brown discoloration in fiberglass lots of times, with no metal nearby, I don't know why, but it seems brown discoloration isn't all that rare.
My SS plates were 29 yrs old when they came out, boats of my type had broken plates at half mines age, but mine truth be known appeared to be serviceable, but without removal, how are you to know?

I think before I Spent that time and money I'd at least see if there is a history of that particular boat breaking chainplates, if there isn't any history, I Don't know that I Would jump on pulling them .
If there is a history, Id be far more likely to pull them.
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Old 22-08-2018, 14:24   #15
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Re: Chainplate how bad ?

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Originally Posted by a64pilot View Post
The sealant is to keep the salt out, the salt is an electrolyte if you will and is the real enemy

however I have seen brown discoloration in fiberglass lots of times, with no metal nearby, I don't know why, but it seems brown discoloration isn't all that rare.
Yes, salt is an enemy but ss will corrode even in fresh water if oxygen starved. The broken shaft photo I posted earlier was on a fresh water boat that had been in the water but not moved for 7 years. The shaft broke on start up inside the cutless bearing where it had been starved of oxygen.

Brown discolouration is not only associated with metal corrosion but is often the result of decaying core materials i.e. balsa and plywood.
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