Chainplate how bad ?

[a64pilot]

When we were discussing my plates a couple of years ago it seemed worst case was oxygen deprived, and in a salt bath.
Then it was discussed that once the salt was present even if there was zero water, the salt would pull enough moisture out of the atmosphere to create a cell and accelerate corrosion, a double whammy if you will, and my chainplates were definitely leaking, I had the water stains in the boat to prove it.
I think they are also subject to stress corrosion from high cycle fatigue, I cant account for my boats plates being OK and leaking, where other IP's half her age had broken theirs. My boat wasn't sailed very often at all, and wasn't subjected to high cycle fatigue.

But either way, there are scads of 40+ yr old boats out there with original plates, that just don't break, and other boats seem to have serious problems at 15 yrs or so. So design seems to play some role too.

[NevisDog]

So, those brown stains may not be rust - could as easily be from the stinking brown liquid that forms osmosis? I've sure seen/smelled brown crud oozing from fi-glass blisters before (but that was below the waterline). So maybe he needs more certainty before tossing all his chainplates overboard?

[a64pilot]

The problem as I see it is, you don’t know until you remove them to inspect, and that can be a lot of work if so do you save a few bucks and put old ones back if they look good, or do you spend a few bucks and go with new?
A decision each person has to make themselves. A lot has to do with intended use.
I not know enough to advise.

However if there were a bunch of those particular boats made, and nobody has ever heard of a chainplate failure, I don’t think I would dig them out, but as in my boats case that chainplate failures are a well documented fact, that’s different.

[Nicholson58]

SS chai plates of a certain age are auspect. I removed mine and polished with a DA sander using 400 grit and finer. I could see the crack all around both sides located within the deck. This is intergranular corrosion. TEAR ON THE DOTTED LINE. I replaced all with new material. In my case, I used grade 5 titanium. 316L is OK for most boats. If you wer able to knock off bits of material I would be very afraid of these plates.

[BrightSEALAB]

Originally Posted by Nicholson58

If you wer able to knock off bits of material I would be very afraid of these plates.

I gathered the OP was using an angle grinder with maybe a flap wheel to pare away some of the deck. This would take the corner off even titanium chain plates without any real effort.

As for the original question... if you believe the metal bars are otherwise sound, that little buzz you gave this one isn't going to cause you any problems. Could get all nitpicky and say that to truly get the best corrosion resistance it will need to be polished to a mirror finish ... but come on.

When were your current chain plates installed? Whatever, in a few years they will probably be of a good age to replace anyway. Put it on your calendar.

[paulajayne]

Originally Posted by a64pilot

but radius it out and polish it, then it won’t be a stress riser, meaning a crack won’t propagate from there.

^^^^^^^


THIS

[Nicholson58]

Originally Posted by BrightSEALAB

I gathered the OP was using an angle grinder with maybe a flap wheel to pare away some of the deck. This would take the corner off even titanium chain plates without any real effort.

As for the original question... if you believe the metal bars are otherwise sound, that little buzz you gave this one isn't going to cause you any problems. Could get all nitpicky and say that to truly get the best corrosion resistance it will need to be polished to a mirror finish ... but come on.

When were your current chain plates installed? Whatever, in a few years they will probably be of a good age to replace anyway. Put it on your calendar.

Have you ever handled titanium plates? Extraordinarily difficult to machine even with carbide tools and cutting fluid on a Mazak. My four plates took eight hours with a skilled machinist and modern NC machinery. They could not be touched with hand tools.

The issue is not the corners you see on this pls SS but microscopic intergranular cracks caused by oxygen depletion in the zone you cannot see. The plates must be removed and polished to reveal the crack. On plates this old, like mine, they are likely there.

[NevisDog]

Originally Posted by Nicholson58

Have you ever handled titanium plates? Extraordinarily difficult to machine ...

Difficult to "machine"... due to spring-back, lack of heat dissipation, etc, etc, but not due to hardness. I think if you just want to hack at it with a grinder you won't find much resistance. Some steels are harder.

[a64pilot]

Grade 5 Ti is the most commonly used Ti in Aviation, and I can tell you that it’s extraordinarily difficult to machine, the feeds and speeds have to be turned way down compared to 4140 steel, way down.
The center section spar on an S2R-T660 will take a day or so to machine in 4140 and a couple of weeks in grade 5 Ti.

[NevisDog]

"Although titanium has gained a reputation of being an extremely strong material, most steels are stronger. The only advantage titanium has over steel is that it is a much lighter material." Also it's very corrosion-resistant.

Titanium is however extraordinarily difficult to machine to a precise profile for a great many reasons, but hardness is not one of them.

[a64pilot]

Hence it’s use in aircraft, and boats

[NevisDog]

Originally Posted by a64pilot

Hence it’s use in aircraft, and boats

No one doubts that a64 - the question was whether Ti was more resistant to an inadvertent attack from a grinder; I think not but, either way, "machining" should never be confused with "grinding".

[Jim Cate]

Titanium is great stuff, sho nuff, but for most boats the advantage is pretty small. Unless the chain plate design is pretty simple, machining costs are high as noted above, and if welding is required, more so. Stainless has (for most boats) proven adequate, and now with 2205 duplex coming down in price, even longer lifetimes are likely. I'm quite happy with my 2205 chainplates, now over 28 years old and much used. Had them out recently and they were as new: no pitting, no cracks, no elongated holes, still shiny!

Had they been fabricated from Ti, all the same would likely be true, save the "shiny" bit. They would have cost more, been no stronger (in a meaningful way) but would have saved several pounds each. That would be nice, but hardly noticeable on my boat, even though she's pretty light for a cruiser.

Jim

Late edit: I see that Grade 5 Ti is in fact nearly twice the tensile strength of 2205. It has less elongation at failure than the s/s, and depending on the application this can be good or bad. For chainplate replacement, if the original 300 series plate dimensions are followed, either material will be considerably stronger, and thus should be more than adequately strong.

And re shiny: no personal experience, but others have reported here on CF that polishing Ti (unknown grade) is difficult... not that shiny is all that important!

[a64pilot]

Grade 5 Ti is roughly equal in strength to grade 8 steel, and grade 8 bolts are awfully strong.
But where Ti really wins is it’s almost complete resistance to corrosion.
Welding isn’t all that bad, the price for all eight of my chainplates to be made from Ti, with significant welding was a couple of hundred bucks more that from 316L from Garhauer.
Now if your plates aren’t encapsulated and therefore starved for oxygen and if they don’t require a tremendous amount of work to get to and or inspect, IE ground out of the hull, then you may not need or want Ti.
The additional cost for the plates to be made from Ti on my replacement were I kid you not, less than 3% of the total cost of the replacement, about 2% actually.

Oh, and Ti can be shined like chrome if you like, I have a 30 yr old polished Ti Lightspeed bike that is as shiny today as when it was made, cause Ti doesn’t continue to corrode.
It actually is extremely acceptable to corrosion, it corrodes in literally milliseconds, form a protective coating and stops.

[Stu Jackson]

Originally Posted by NevisDog

>>>>>>>>

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?

Doesn't there need to be "somewhere" where the "line" of waterproofing exists?


It appears, although we don't know for sure, that the entire depth of the deck has been glassed around the CP. It could be only the surface layer, right?


Somewhere along the line (pi) there has to be waterproofing to keep it dry down below. Waterproofing indicates a need for a tight seal, no?


I think the difference here is that we are all, or most of us, assuming that the encapsulation is complete for the depth of the deck surrounding the CP.


Could be, but...


Here's what I did with a similar "design" of CPs:


Chainplate Rebedding 101 - with Bed It with Butyl from Maine Sail

C34 mark 2 chain plates leaking - Chainplate flix