Chain plate questions:

[Bowdrie]

Originally Posted by Chotu

So, our chain plates working by friction?

No, the idea of "friction" is delusional.
A slippery stainless surface against a smooth fiberglass surface does not generate anywhere near enough "friction" to overcome the loading tension of rigging.
At best there is some shear strength from the caulk, but only if it's a highly adhesive caulk like 5200, and compared to rigging loads it's small.
Bolts in shear take the loads, all the loads.
The idea of grinding away large areas of the structural plywood to replace with a dis-continuous fiberglass surface is likewise a fools errand.
You have a relatively thin fiberglass covering on top of plywood, unless the fiberglass is quite thick it offers minimal strength, the strength is in the plywood structure.
Epoxy plywood backings to the inside of the hull structure where the chainplates go, laminate if necessary to follow hull shape.
Question: are there longitudinal stringers inside the hull sides?
Question: how thick is the plywood where the chainplates go?
If the top bolt of the chainplates can go thru the sheer clamp, so much the better, it offers much strength.
With the plywood structure their is no need for fancy compression sleeves. The chainplates need to be long enough to transfer the loads in the vertical.
Fore-and-aft not as much.
What does the designer spec-out?

[Benz]

Originally Posted by Chotu

Question about this one. It’s a nice idea. I like the sound of it

But I already have local core in the boat that’s the right density for the chainplates. It was put in during the hull infusion process.

It won’t crush anyway. It’s straight from the plans.

Still a good idea?

It seems like things may crush a tiny tiny bit when the large part of the chain plate is tightened down, but then these G10 tubes will create hard spots instead of evenly distributing the crush load. This would cause less friction and an uneven pressure across the area the chainplates press on .

So, our chain plates working by friction?

It's still a good idea to keep the holes from letting water into the core, even if crushing is a non-danger. The G10 makes a nice bearing surface for the bolt, and a good load transition from bolt to hull. If you sand them flush with the surface, and the surface can't crush, everything should be perfect.

[Cheechako]

Epoxy resin is brittle and has no strength on it's own. If you must drill oversize you should put something in the resin, then final drill after it sets.

Friction is real and I have no doubt that it is a combo of friction and bolts. If you dont think friction is real try parking a car on ice. There is a ton or two holding it down, but on ice you could spin it by hand.

I often wonder if making 'donuts ' out of epoxy for cored holes is a good thing. Is it better than just saturating the plywood with epoxy and in the hole? Not so sure, and without some filler it can't be good. Not to mention you can make a 2 day job out of mounting a simple fitting on deck.

Why not 5200?
Glue a wood block to smooth fiberglass with 5200, then one with epoxy resin. With epoxy you can tap it off with a hammer readily. If there were to be some movement, 5200 will stretch and has some elasticity. Epoxy resin has almost no movement potential.

[Chotu]

Another question. When I stick the chain plate on the outside for the final mount, what do I stick it into? Bog? 5200?

I guess what I’m also asking is, can I build up all my layers of plywood and fiberglass, then let that kick, then position the chain plate at the correct angle, then do my drilling, and then bolt it on bedding it into 5200?

[Chotu]

Actually, I may have answered my own question.

My last post asks about bedding the chain plate. It has some large bog “bolts” as part of the design. Made with structural filler. Should I use glass fibers there? It definitely beds in bog.

Does that mean the whole thing has to go wet on wet? Or does it mean I can do the build up, then a secondary bond to put the actual chainplate on for the final bolt down?

My designer is great at coming up with light, strong things and drawing them. Not so good at letting you know how to make them. Ha ha

Then my bolts themselves are 1/4”. Can I get G10 or FRP tubing in 1/4” ID? Can i get it fast somewhere?

Need it ASAP. Anyone know where to pick it up? It’s small stuff.

[MicHughV]

Without knowing more about this..or other chainplate locations, nor knowing the details of how the boat was constructed, hull thickness, where support beams are, the hull/deck joint, etc, plus we don't know much about the chainplate either, it's orientation to the hull and rig, etc., will it be holding only one stay/shroud or two, the angle of the stays in relation to the deck, etc.......number of bolts, size of bolts, bolt pattern on chain plate, clearance from top bolt to deck, distance between the bolts, etc. Finally, we don't know what the anticipated load on the chainplate will be....nor have seen any talk about safety factors...

The load on a chainplate...especially on a cat can be extraordinary, 1,000's of pounds and one must factor in a shock load to boot.

To really get an honest opinion on what will be required would require a visit to the boat and some input from the nautical architect on anticipated rigging loads.

I don't understand how the nautical architect has not already addressed this situation for you with some detailed plans or instructions ???

[Chotu]

Originally Posted by MicHughV

Without knowing more about this..or other chainplate locations, nor knowing the details of how the boat was constructed, hull thickness, where support beams are, the hull/deck joint, etc, plus we don't know much about the chainplate either, it's orientation to the hull and rig, etc., will it be holding only one stay/shroud or two, the angle of the stays in relation to the deck, etc.......number of bolts, size of bolts, bolt pattern on chain plate, clearance from top bolt to deck, distance between the bolts, etc. Finally, we don't know what the anticipated load on the chainplate will be....nor have seen any talk about safety factors...

The load on a chainplate...especially on a cat can be extraordinary, 1,000's of pounds and one must factor in a shock load to boot.

To really get an honest opinion on what will be required would require a visit to the boat and some input from the nautical architect on anticipated rigging loads.

I don't understand how the nautical architect has not already addressed this situation for you with some detailed plans or instructions ???

My designer is too good to give you instructions. Lol

He gives you detail plans and drawings.

But nobody here needs to know any of what you are saying. This isn’t a thread where I’m asking how to make a chain plate. I already have the plans. I just asked how to close out the core which is plywood on the build up.

Then I also asked what type of structural filler I should use where they call for it. Wondering if I should use glassfiber instead of just colloidal silica.

My other question was that I was curious if friction or the bolts hold the chain plate. I have seen people say one or the other. And argue with them pretty well. No idea who is correct. But I’m curious.

That’s it. I didn’t ask how to make a chain plate. I’m not deviating from the plans. Other than reversing them. The plans I have have an internal chain plate that goes through the deck. Stupid. So I’m putting that on the outside.

You are one of my favorite participants in my threads. You practically designed the entirety of my dinghy davits. Remember that one? I put some pictures up later too. Pictures of the finished product. They came out great. We were discussing aluminum at first, and then I changed over to pultruded fiberglass tubes? Remember that? Cantilever? They are awesome.

But this is not that kind of thread. These are already designed. I just have questions about the assembly. And sourcing materials.

Maybe in my first post I should start mentioning in bold letters if I am asking how to design something, or just how to put something together. Because this isn’t the first time this type of confusion has happened. And if that’s the case, it’s my fault for not being clear enough.

And I can’t share the exact details of my chain plates here, because that would be a violation of my designers intellectual property rights. I don’t really like the guy, but I would never do that to someone. He’s very good at his job, and he put a lot of work into coming up with one hell of a boat. One of the lightest, strongest structures possible. It’s brilliant. He deserves to make money selling plans for that.

[rslifkin]

Generally I default to bedding hardware in 4000UV unless I have a reason to use something else. It seals stuff, it's white so a tiny bit visible at the edges doesn't look bad, and for the situations where it matters, it's sticky. Backing plates get attached / bedded with thickened epoxy so they effectively become part of the structure.

I'm no expert here, but I can't think of a good reason why a part that may someday need to be removed/replaced would need to be bonded to the outside of the hull with thickened epoxy or anything of that nature unless the shape of the contact surface was a hair off between the 2 parts and you wanted something more solid to effectively correct that.

For at least some metals, the 3M data shows 4000UV having a stronger bond than 5200. I can't remember if that's the case for stainless, but it definitely is for aluminum.

[Madehn]

Personally i would seal the chainplate to the hull with 5200. as far as the plate and the drilling go i really like the idea of drilling an oversize hole from the inside but not drilling through the outer hull-- fill that with thickened epoxy, sand flush on the inside then drill through it. if you want belt and suspenders, add a backer plate of GP 03 or even G10 to the inside which is glued (or 5200) to the plywood. Make that backer plate large so that it can help spread the loads as much as possible. This might be overbuilt- i tend to make things way too strong but then i don't have to worry about them. how big did you say your bolts were?

[seandepagnier]

As far as what is holding it.. it's not the bolts in shear, but the friction of the chainplate against the hull. So the bolts are in tension only. At least this is my understanding.. is it right? imagine if the bolt itself were pulling up, this would be a lot weaker and push against a potentially softer core. This is why you need to tighten the bolts really tight.

Sorry if this thread isnt all about the OPs questions as I also have chainplate questions.

I just got 6" by 24" plate pieces of titanium grade 5 for $60 each. Each one can make a few chainplates. This was half the price of 316.

stainless seems not the best material because of crevice corrosion and the fact you need to passivate it. Same reason it isn't the best material for standing rigging either.

The issue with titanium is its actually quite difficult to cut. I would say more difficult than 316 stainless which is not exactly easy. I am struggling with that as it took me 20 minutes to cut 5 inches.

Before I always used silicon bronze. Much easier to drill and cut. This is really a great material I would prefer over 316 any day. No need to passivate, and you can easily anneal it and bend as needed. No worries about crevice corrosion either. With 316 (correct me if i'm wrong) you need to anneal to bend more than 15 degrees or so, and its not really easy to do this.

Sorry if I assumed 316, if you are using 2205 or something else.. where did you get it?

[Madehn]

i looked again- the bolts on your chainplates are only 1/4 inch. seems very small- my chainplate bolts are HUGE compared to that-- different design i get it but 1/4"

[Chotu]

Originally Posted by rslifkin

Generally I default to bedding hardware in 4000UV unless I have a reason to use something else. It seals stuff, it's white so a tiny bit visible at the edges doesn't look bad, and for the situations where it matters, it's sticky. Backing plates get attached / bedded with thickened epoxy so they effectively become part of the structure.

I'm no expert here, but I can't think of a good reason why a part that may someday need to be removed/replaced would need to be bonded to the outside of the hull with thickened epoxy or anything of that nature unless the shape of the contact surface was a hair off between the 2 parts and you wanted something more solid to effectively correct that.

For at least some metals, the 3M data shows 4000UV having a stronger bond than 5200. I can't remember if that's the case for stainless, but it definitely is for aluminum.

Well, in the plans, there are quarter inch bolts that bolt through the hull. And then there are these sort knobs I guess you might call them, made from structural filler epoxy. These knobs are 3/4” and have their own holes in the chain plate as well. So I don’t see any other way around it.

I believe it’s a pretty smart technique used to do away with a bunch of metal. So it’s not as heavy. Every pound counts. That’s the way the whole thing is designed.

[Chotu]

Originally Posted by seandepagnier

As far as what is holding it.. it's not the bolts in shear, but the friction of the chainplate against the hull. So the bolts are in tension only. At least this is my understanding.. is it right?

I just got 6" by 24" plate pieces of titanium grade 5 for $60 each. Each one can make a few chainplates. This was half the price of 316.

stainless seems not the best material because of crevice corrosion and the fact you need to passivate it. Same reason it isn't the best material for standing rigging either.

The issue with titanium is its actually quite difficult to cut. I would say more difficult than 316 stainless which is not exactly easy. I am struggling with that as it took me 20 minutes to cut 5 inches.

Before I always used silicon bronze. Much easier to drill and cut. This is really a great material I would prefer over 316 any day. No need to passivate, and you can easily anneal it and bend as needed. No worries about crevice corrosion either. With 316 (correct me if i'm wrong) you need to anneal to bend more than 15 degrees or so, and its not really easy to do this.

Sorry if I assumed 316, if you are using 2205 or something else.. where did you get it?

I don’t have a clue. I’m not bending it. The fabricator is. I don’t have that kind of equipment.

And I agree with you completely. I would absolutely love to use titanium. Where did you get it?

[rslifkin]

Originally Posted by Chotu

Well, in the plans, there are quarter inch bolts that bolt through the hull. And then there are these sort knobs I guess you might call them, made from structural filler epoxy. These knobs are 3/4” and have their own holes in the chain plate as well. So I don’t see any other way around it.

I believe it’s a pretty smart technique used to do away with a bunch of metal. So it’s not as heavy. Every pound counts. That’s the way the whole thing is designed.

Hmm... Those knobs sound kinda like load bearing locator studs. I assume the bolts don't go through the knobs?



I don't know how practical it would be, but I'd think it would be stronger to make the knobs from G10 rod going through the hull and backing plate vs just building up thickened epoxy for them.

[Chotu]

Originally Posted by Madehn

i looked again- the bolts on your chainplates are only 1/4 inch. seems very small- my chainplate bolts are HUGE compared to that-- different design i get it but 1/4"

Yeah. Just a really different design. I have about 5,000,000 1/4 inch bolts.

Then as I had described a little earlier but you hadn’t seen, I have three-quarter inch composite epoxy knobs which are kind of like bolts in a way. A whole bunch of those also.

I think the design I’m describing actually says that it’s not friction.

It’s relying on the structural integrity of those knobs that are being pulled on by the shroud.