Chainplate ideas

Have been thinking...(some would say be careful...that's dangerous for you Ranger)...nonetheless,my thoughts HAVE been mulling over the issue of chainplates and there ability to corrode and fail severely and dangerously.Now-i'm no expert,and correct me if i'm wrong...but the biggest cause of chainplate failure is they seem to get corroded or suffer from corrosion which then weakens the metal causing it to crack and fail-sometimes dangerously and catastrophically-when you least need it to happen!At sea, n.miles from anywhere.
So-my thoughts followed this path...
If the material used fails when it gets corroded what can be done to stop it getting corroded.I know that there are composite materials that are being used in chainplate fabrication but to my knowledge they are quite expensive.So my idea is this...why not get 316ss and just simply put a hardwearing powder coat on it?This way anyone who has a bit of skill with there hands can buy the right width and thickness of 316ss in a bar/strip and cut it to the shape,size you need,drill the holes slightly oversized (for taking into account the powder coat) and then powder coat your metal.There are various different powder coats on the market and this would stop or at the very least slow down the corrosive effects of salt water/fresh water on the material,there by prolonging its life.It would also be better for sealing the chainplate as well.
Am i way off the mark here?
I would love to hear any and all opinions from you guys about this.
Thanks.
Quick add on:-I guess the only thing that wouldn't be convenient is the fact that you couldn't see the chainplate to visually inspect the material to see if it has any cracks are failure in it...however,i have seen pictures where the chainplate failed below the deck planking but above the inside/bulkhead!!

 

316S is a passivated steel and very corrosion resistant. All stainless need oxygen to form a layer of protective oxide. Otherwise you will get crevice corrosion and the fitting will fail. Bronze and Monel have higher corrosion protection and used to be very popular.

 

Would the same apply to 304ss?
I know that bronze and monel are very good performers when it comes to corrosion.Bronze has been about for years-the Royal Navy loved it..Bronze isn't as 'tough' as steel and as far as i know has to be cast doesn't it?And monel is apparently quite expensive,as is bronze-but not prohibitively so.They are indeed both viable alternatives.
All the evidence of chainplate failure i have seen points to ss as eventually shearing and it seems to be mostly due to corrosion weakening the material and then having individual loads placed on it.
This was just a thought about powder coating and it arose via a friend i have who used to work in a tail lift company-they powder coated the parts that were involved in heavy duty lifting and that were also constantly in an open exposed environment-obviously not a salt water environment,but an exposed to all weather environment nonetheless.
Just an idea.....

 

Ranger,

Corrosion is certainly one of the failure mechanisms, but so is work hardening. Of course I am prejudice, but I think the best solution is to just switch to titanium instead of stainless. When properly redesigned titanium chainplates can get very close to the same price as stainless, but have none of the corrosion problems, at a fraction of the weight.

 

If, as you suggested, are going the route of rebuild old wooden hull you might also consider using iron for the hardware. Cheap and easy to work with.. did I say traditional?

 

Powder coating is great for some purposes. I think chain plates would not be one of them. With powder coating you might have any type of impact to the plate that would cause a void of some type. Then you would have the possibility of corrosion happening under the powder coating going unnoticed.

 

Agreed, corrosion can be a problem, but fatigue is the big one because it can couple with corrosion and accelerate issues. 316L would be my choice for economical chain plates. 304 has no business on any ocean going (salt) craft. Iron requires the same scantling approaches as lower grades of stainless. You just make them thick enough to accept some corrosion during it's life span. Titanium can be spec'd to rival good stainless in cost as can some composites, though you do need them properly engineered. Bronze and Monel are great, but often cost prohibitive. I've never seen a coating on mild steel work well, except galvanizing. You can get long life from well sized galvanized steel, but you'll have to live with some staining.

 

http://duckworksmagazine.com/12/howto/chainplate/index.html

 

Bronze , use a good size and install proper toggles on each turnbuckle to keep loads down when folks push the boat off a dock by pushing on the rigging.

 

Composite chainplates can be a good option if they're designed as an integral part of a composite hull.

Carbon and other advanced fibres don't like bolt holes, though; for bolted-on chainplates my vote is still with metal.

Bronzes are my #1 choice (and yes, you can fabricate them from bar stock, they don't have to be cast).

Titanium is great if you have the budget for it and can find someone who knows how to work it- many machine shops, and most welding shops, have no clue what to do with Ti alloys.

316L stainless is perfectly serviceable if it's properly fabricated (no cracks or crevices for corrosion to start) and properly installed (anti-corrosion gel on all the fasteners, etc.) There's no need to coat or paint 316 SS. And skip the lesser grades (304 or anything from the 4xx series) as they don't get along particularly well with salt water.

 

Material options abound with chain plates, it's the sizing that's key, particularly for differing materials.

 

Noted.However,some of the powder coatings available on the market today are extremely resilient to impact and if one was to use a double coating of powder and then 'dip' the material in a rubberized compound i think that you would have an extremely hard-wearing end product.I may get a 'test' chainplate to see how viable it would be under real world conditions.Granted,there is always the possibility of having any type and number of impacts upon the chainplate,but in general i believe that as long as you used the right type of coating it 'should',as i say,be quite resilient to wear and tear.Maybe one problem would be 'chafing' and the wearing down of the coating in the holes through movement (with the clevis pin).
These are only ideas.My primary concern is how to stop or at least prevent corrosion.
Also how often is it advisable to completely change out the chainplates?

 

There's really only two ways to address corrosion on a chain plate, eliminate contact points or use a noble metal. Any coating, regardless of type will be hard pressed to withstand the abrasion of the pin, so this is where the coating will get breached first, then corrosion begins. Properly size, bronze and monel plates have stood the test of time. Ti is a possibility and 316 or 316L stainless also has faired quite well. Corrosion prevention is also a function of maintenance. If interested in the least amount of effort in this regard, a noble material is required, not a coating.

 

hi all...
hopefully not an outright hijack, but a side step to be sure. im building a 40' cutter and planning to incorporate carbon chain plates. the boat is wide open, access to the newly installed bulkheads (1" laminated marine doug fir ply) is cake. ive got a bunch of 13oz 1" uni tape and pretty much have my head around the process. for something like chainplates my philosophy is one of 'overkill begets peace-of-mind'. is there an on line calculator that might get me close? or some sage boatbuilder whose been there before? yeah...ill end up paying an NA for this and other things, just looking for a ball park. the boat will splash at about 9tons, 6500lbs of ballast, 45' stick. if i build up 1/4" over the pin and down both sides of the bulkhead, fanning the tails out over several square feet each side, does that sound like overkill? is it necessarily true that 1/4" carbon is as strong (in tensile) as the equivalent section of 316? the originals where 1/4" stock and im using that as a starting point.

no back to our regularly scheduled program...

 

Rob,

It very much depends on the specific layup, resin, and cloth used, but a tensile strength of 500,000psi is reasonable for CF, compared to 35-40,000 for stainless and roughly 138,000psi for titanium.

But there are a lot of other issues involved, including the fact that CF is very bad at handeling shock loads, and impacts. It isn't quite as simple as just reducing the cross section area by a factor of ten and being done with it. In some applications you may need thicker CF than steel, and in others you can get away with less.

There are also issues with fatigue life that can be designed around in metals, but not CF.