Chainplate Failure and Concerns

[dadidoc]

I now have 8 brand new 1/2 inch thick and 12 inch long chainplates to put back on my Morgan. I took off a few more, cleaned them in a citris passivation bath, and found cracks in each.
I now have chainplates better than the OEM, made by water jet cutting, holes drilled with special bits vs being punched, and I do not have the concavity formed on the back of the plate due to punching. I started this whole thread, and you all should know that I am replacing all my chainplates !

[theonecalledtom]

Got my first quote today for CP replacements. 2-300$ a piece depending on polishing which I was told is the most intensive part.

I'm looking to replace 6, so this is painful!

Talking a metal yard I can get enough 316 for the job (all 6) for $120.

Does the approximate quote seem a bit over the top?

[theonecalledtom]

oh - 20" X 2" X 1/4" 316 with 6 holes a plate

[osirissail]

Originally Posted by theonecalledtom

Got my first quote today for CP replacements. 2-300$ a piece depending on polishing which I was told is the most intensive part.
I'm looking to replace 6, so this is painful!
Talking a metal yard I can get enough 316 for the job (all 6) for $120.
Does the approximate quote seem a bit over the top?

No, not really. Besides being dead sure that the fabricator of the new chain plate follows the constraints and requirements for hole placement and metal required between the hole placement and the edges of the chainplate - the polishing is really where all the labor is involved.
- - Stress analysis for hole and shape can be referenced from Brion Toss's Riggers Apprentice book - not a small tomb but contains all the information and formula for making a viable and serviceable chain plate.
- - I normally polish all the stainless steel myself starting with the rolled plate cut and holed to specifications. The polishing normally takes me almost a week to work my way from 120 grit down to 2400 grit polishing paper which yields mirror bright finishes. Skipping any steps doesn't work as you spend twice the time and paper trying to make up for the missed grit step. I do use orbital electric finishing sanders and plenty of water on the surface when I get down to the finer grades.
- - In other words, the finishing is very labor intensive and if purchased would be a major price factor. If you do it yourself, your labor rate is zero so that cost is saved.

[silverp40]

You can also purchase 316L stainless with a very small increase in cost. This would be more corrosion resistant than 316 with same strength. If the steel is manufactured in the USA it's even better...

[silverp40]

Here is a pic:

[theonecalledtom]

Originally Posted by osirissail

No, not really

Sadness. We don't have nifty machines that you can just pop the pieces in and have them come out all shiny these days?

Because of some other things going on my life this means I'll probably have to spread out the spreader replacement, two at a time. Luckily the others look in better condition, but I don't really trust them anymore!

[dadidoc]

It is me again.
Reading from the start of my post - lost of interesting stuff - lots of misleading info too.

I would not worry about "polishing" - I think it is more important to passivate. I used Citrisurf and they came out cleaner and they were properly etched by the citric acid to remove the metals that you guys are embedding when you use sandpaper and brush wheels to polish.

I skipped a step, but wish I had my 8 new chainplates "shot peened" which would have strengthened the plates and made them more resistant to stress corrosion.

I am now finishing up an tuning my rig -feel better with all new main plates on my Morgan 416 - now I need to tackle the mizzen.

[osirissail]

Originally Posted by theonecalledtom

. . . Because of some other things going on my life this means I'll probably have to spread out the spreader replacement, two at a time. Luckily the others look in better condition, but I don't really trust them anymore!

You list yourself as being in Southern California. If you can get the dimensions of your old chainplates and then email or call the appropriate vendors from NavTec/Norse/Gibb in the link you can request a quote on cutting and polishing new chain plates from them.
- - I have used their Florida listed outfits quite successfully when redoing the rigging for customers. Or, at least I found the Fla listed dealers to be quite responsive and helpful.
Sales/Service Locations - Navtec Rigging Solutions

- - If nothing else you will have a quote from which you can make comparisons to other shops that are willing to make the chain plates.
- - As far as polishing is concerned, properly done it will result in a layer of pure chrome oxide on the surface of the chain plate that will help protect the metal from intragranular corrosion. Passivation is the stand alone process of chemically removing the iron from the surface of the metal and leaving the chrome component behind to provide protection. But anyway, shiny chain plates look nicer and more professional. Who wants an ugly boat?

[CSY Man]

Passivation is the stand alone process of chemically removing the iron from the surface of the metal and leaving the chrome component behind to provide protection.

I had my (new) 316 SS chainplates electropolished..Looks good, last a long time and a hell of lot less work than trying to polsih to a chrome like finish.

[osirissail]

Originally Posted by CSY Man

I had my (new) 316 SS chainplates electropolished..Looks good, last a long time and a hell of lot less work than trying to polsih to a chrome like finish.

Yes, Electropolishing is the "knat's ass" way of doing a good job. Which means it is the best and accomplishes the objective of obtaining a continuous chrome surface finish without have to resort to mechanical means. It also allows you to have a brushed surface finish which can be more attractive (to the eye of the beholder) than a mirror finish. Unfortunately, not every shop has the equipment to do electro-polishing and some that do have the equipment do not maintain it properly.
- - Mirror finishes are obtained mechanically followed by an acid bath to remove any remaining iron/steel from the surface. The mechanical polishing smears the chrome over the surface to try to seal in the iron/steel below. Unfortunately it is mechanical and as such there are bound to be microscopic gaps between the chrome parts of the finish. So how long a mechanical polishing will last is variable whereas electropolishing can usually obtain a much longer "stain-free" finish.