E38-200 replacement aft chainplate

[Kenneth K]

The chainplate has to line up naturally before holes are drilled, and I think Ericson was casual about that in my case. If slightly askew when bolted down the strain isn't even on the steel.

If re-locating the holes to "line up" the chainplate, it's probably a good idea to check the rigging first to ensure the top of the mast is where it's supposed to be.

Also, a note to the owner, Eric: It looks like the chainplate screw heads have been messed with a bit (post #14) and the original backstay has been altered (post #1) with a Sta-Lok fitting (vs the factory swaged fitting). Might be worth getting the rig checked out if a previous owner made changes to it.

 

[Pete the Cat]

I think the most important thing, when reinstalling, is to insert the lowest bolt first, then tension the backstay. Or maybe the top bolt first, not sure it matters.

The chainplate has to line up naturally before holes are drilled, and I think Ericson was casual about that in my case. If slightly askew when bolted down the strain isn't even on the steel.

Rather than worry about the type metals, I would likely fill all the current holes with hi density filler and possibly look at the backing plate situation for improvement while it is all apart, and then follow Christian's advice. This is not a great design from Ericson or King, but they built boats to a price they eventually could not afford. Ideally you would anchor the backstay like you do a staysail stay; there would be a straight shot to a small bulkhead glassed to the hull. But that would be very expensive to pull off. And many production boats have funky arrangements like this so I think it is something for all of us to watch. Appears to my untrained eye that there was a serious flaw in the original metal--that gap looks like more than a crevice.

 

[footrope]

I like the titanium idea, perhaps because I had my forestay chainplate duplicated (same thickness) in titanium back in 2017. No countersinks. It took a month, by Colligo Marine in Grover Beach, CA. Alignment, as mentioned in several posts, should be corrected if necessary.

Craig

 

[EricHasAnEricson]

@Kenneth K - the sta lok was me. I just replaced all the standing rigging.

Update on my situation: I found a local welder to shore up my existing chainplate in the meantime. Going to go the titanium route, it's not much more expensive, and I'm sold on the efficacy of grade 5 Ti vs 316L.

Looks terrible, but strong enough (for now). For the new chainplate I intend to take 5° off the bend - like others here, mine does not match the angle to the masthead. I'm also going to get rid of the countersunk holes, and use grade 5 Ti bolts with stainless nuts.

Thank you all for your ideas, recommendations, and feedback. I really appreciate it.

 

[Christian Williams]

Can someone explain to me the need for long chainplates, with six holes?

Does such a design actually spread a load?

What are the chances that all six bolts share equally the force upon the chainplate?

The design is traditional and ancient, I just don't get it. Would a chainplate twice as long be stronger? Would a chainplate half the length, with only three bolts, be significantly less strong?

 

[bgary]

Does such a design actually spread a load?

I wondered the same thing, and also while considering the "angle" question farther up-thread.

In particular, I wonder if there is some sort of engineering magic involved in *not* having the chainplate angle neatly line up with the load.

It might be that having the angle slightly beyond the line of the backstay creates some compression-load against the transom surface at the upper end, rather than straight line of pure tension-load along the line of fasteners.

....or, I might be giving Ericson too much credit, and they shipped several thousand boats will ill-designed backstay chainplates. Dunno.

 

[Pete the Cat]

Can someone explain to me the need for long chainplates, with six holes?

Does such a design actually spread a load?

What are the chances that all six bolts share equally the force upon the chainplate?

The design is traditional and ancient, I just don't get it. Would a chainplate twice as long be stronger? Would a chainplate half the length, with only three bolts, be significantly less strong?

I am no engineer, but I would suggest that the length and number of bolts is more related to spreading the load to the hidden backing plate, albeit unevenly. I also believe that the mainsheet, vang and aft lowers, mitigate some of the force on the back stay puts at this point, but it still seems like something to monitor.

 

[Kenneth K]

I am no engineer, but I would suggest that the length and number of bolts is more related to spreading the load to the hidden backing plate, albeit unevenly.

Yeah, I think the large number of bolts is due to the relatively weak fiberglass (versus steel) being the mating material. The steel strap doesn't need 6 bolts but the fiberglass hull does.

 

[Christian Williams]

That makes sense. Our forestay chainplates wrap around the bow and continue down the stem nearly two feet. That must be spread to the load over the hull, not the steel. Similarly, my model has long chainplates in the cabin, led up to rods through the hull. The chainplates are attached to mere plywood bulkheads less than half an inch thick. The length spreads the load on the plywood, not the stainless.

I feel better now. Yes, you may say, but there is still a long way to go.