Crevice corrosion...

[paladin]

Waaaay back in 1969 when I started Neper, the Jim Brown Searunner 31 Tri.....I worried about a problem with the chainplates. The metal was stainless steel, but a bit thin...although quite adequate strength wise. I was aware of the problem of wear on the pins connecting the turnbuckle and toggle to the plate. I was also aware that it is not advisable to weld ACROSS the tang as it has a tendency to crystallize the metal and weaken it.
I made doublers for the end of the plates, bevelled the edges, and welded around the outside of the tangs but not across it. The metal was cleaned and a hydraulic prss held the two pieces together while being welded. The welds were then ground smooth and polished. There was no visible line where the two pieces were not welded.

Today John Marples advised me the chainplates BROKE.....after about 20 years...the problem..crevice corrosion where the two metal pieces were in contact with each other...so now they advise using thicker metal and no doublers to stave off wear at the pin.....

[ssor]

And no way to detect the problem before failure. :(

[kc8pql]

Thanks for bring this up. I'm designing a SS masthead truck right now and was kicking around the idea of using doublers on the stay tangs to save some weight. Crevice corrosion had crossed my mind, but I kinda discounted the thought. Guess I'd better go ahead and use thicker plate.

[ssor]

If weight is a serious concern then the excess metal can be machined away. Tapers and holes are often used to reduce weight and still maintain strength.

[Jay Greer]

Gosh darn dratt! I hear this so often; pocket corrosion attributing to rigging failures! Now hear this!! I have never seen a bronze tang, chain plate or rigging screw fail, ever, due to work hardening, pocket corrosion or just plain corrosion! And that is in over fifty years of sailing world wide. Bronze plate does not need to be elctro polished, passivated . tig or mig welded. Silver solder will do. Bronze plate can be formed with simple tools in the home shop, cut on a band saw, filed bent, drilled, rivited and polished with a simple buffer.
The savings in labor alone is worth the cost of the material. Besides that it is just plain nice to work with!
And, it doesn't fight back like stainless does!

[mmd]

Yeah, but shiny silvery stainless looks so much better with white gelcoat... ;) tongue.gif

[Bob Cleek]

Right on, Jay! Right on! And you forgot one more advantage of bronze: it chrome plates well... if you must!

[Scott Rosen]

Originally posted by Jay Greer:
I have never seen a bronze tang, chain plate or rigging screw fail, ever, due to work hardening, pocket corrosion or just plain corrosion!On my desk at work is one of Patience's original bronze rigging screws (I call them turnbuckles). It's on my desk, not my boat, because it failed. The threads eventually developed so much play, they no longer held.

But, I still prefer bronze over stainless for just about every application, except maybe stanchions, ladders and anchor mounts.

[carioca1232001]

Where in the US may bronze plate be available at a fair price ?

I looked up - was it McGraw Carr ? - and the prices were pretty high.

Anyone know of other dealers ?

Thanks

[sdowney717]

What about using copper plate?
Readily available but would it be strong enough or would it be too soft? I picked up a 4 foot by 4 foot sheet 1/8 inch thick for $40 at a metal shop. Part of a project for me to make a heat exchanger. I rolled it into a tube and used half inch copper pipe for the elements inside. It was large and heavy and it worked out very well.

[Canoeyawl]

I have used this supplier many times...
bronze bar stock, plate, etc.
http://www.alaskancopper.com/

[Bruce Hooke]

Originally posted by carioca1232001:
I looked up - was it McGraw Carr ? - and the prices were pretty high.You are probably thinking of McMaster-Carr. They are a great place to go when you need a huge range of things to choose from because their catalog is enormous. However, their prices are often a bit on the high side...

[ 08-25-2005, 12:07 PM: Message edited by: Bruce Hooke ]

[kc8pql]

Originally posted by carioca1232001:
Where in the US may bronze plate be available at a fair price ?I've used Atlas Metal a few times. They don't seem to mind taking small orders and the price is better than my local non-ferris metal supplier.
Atlas Metal (http://www.atlasmetal.com/index.htm)

[Gary E]

Originally posted by carioca1232001:
Where in the US may bronze plate be available at a fair price ?
There are many places in all of the large US industrial cities where all types of metal is stocked and sold. Finding what you call "reasonable" may be a exercize in futility and then adding in shiping to Rio de Janeiro will make it extreemly expensive. Is there no industry in your country? I can not imagine you not finding material nearby.

Anyone buying metals from the likes of McMaster Car and other such companies knows nothing of where to purchase, or is not interested in looking in the local phone book and is happy paying high prices through the nose.

[carioca1232001]

What I had in mind was installing underwater bronze-plate-cum-pieces-of-tube , right over the twin prop-shafts where they exit/enter the bilge from the underside.

(There are identical bronze pieces inside the bilge, - the latter pieces are refered to as telescópios in Brazil, because they faintly resemble one)

Sdowney717 wrote:


What about using copper plate?.....
Not the best thing for the intended underwater application

Canoeyawl wrote:


I have used this supplier many times... Many thanks.

Bruce Hooke wrote:


You are probably thinking of McMaster-Carr. They are a great place to go However, their prices are often a bit on the high side ...We are in agreement !


I've used Atlas Metal a few times .[/QUOTE}

Thanks !

Gary E wrote:

[QUOTE]..... Finding what you call "reasonable" ...and then adding in shiping to Rio de Janeiro ....extreemly expensive . BRONZE in Brazil - when you are able to locate a dealer - is sold at an obscene price - don´t ask me why, cause I don´t know the answer !

A friend has been a Frequent Flyer for ages - a pilot ? ;)