Would anyone be willing to help me interpret chainplate plans?

[Chotu]

Originally Posted by more

wrong, chainplate must hold force acting on mast and mass of your boat.
For example this boat have close 9000 GT and force on mast xxx ton on wind 20 kt on wind 1 kt only x tons
https://www.total-croatia-news.com/t...onal-sail-ship

somebody with new modern software must calculate force on chainplate. i know for this boat up have book and ship computer for calculating how much must max sail have on xx speed wind and angle. you can change anything but the law of physics is not possible to change or escape. after you have an exact number you decide size and bolt size/material. if you don't have number simply go on similar size of sail cat and make bigger chain plate and terminal post,system.

Also for example old Bavaria have oversized chain plate and all system easy survive 100 knots wind but maybe mast go down on for example 120 knots on 200 knots 100 % mast is down. everything is in calculation,everything have limitation

Well, maybe. That really wasn’t the focus of the thread. I was trying to indulge RSlifkin.

My understanding is the force on the chain plate is the righting moment of the boat. That’s it. How could it be anything else? What is holding the boat down to the water? Gravity. When you grab onto the top of the mast, and you start to pull the boat over, the force you are exerting at the top of the mast is what goes into the chain plate. No?

We are not talking about light wind situation here. I think you’re getting confused actually. There is no 1 knot condition. There is also no 100 knot condition with sails up because the boat is already capsized. We’re talking about necessary strength of the chain plate. That is only the condition where the righting moment is exceeded. The case where the boat capsizes. That’s the most force there is on the boat, unless you tie it to the ground somehow. Or anchor it down. It’s just going to tip over.

Where am I wrong about that?

[Manateeman]

We don’t care who the designer is or how many catamarans he has done but this has got to be one of the silliest chainplates we seen in a long time.
Needlessly complex. Looks prone to leaks, difficult to inspect.
Have your assistant laminate some nice triaxial in epoxy inside the hull. Keep the entire chainplate on the exterior of the hull. Use a backing plate on the interior.
Bolt through with button head bolts and extra heavy nuts inside. Slather it in 5200. If you want a larger surface area for your toggle bolts, double up the top portion of the chainplates and have them welded. We have built silicon bronze chainplates on a glass epoxy hull and you could lift the boat with them. You want high tech bling go titanium. We just see too many too small too complex too hidden too close itty bitty fastenings.
But then again, we like big thick ugly industrial I beams.
This is not rocket science.
Chainplates simply spread the load but the hull must be reinforced. They belong on the exterior of the hull unless the hull is welded.
Look at older wood boats. They did not concentrate the load. Keep the fastenings where you can see them on the interior where you can check them. Simple. Strong. Bolted. Spaced to spread the load.
Principals of Yacht Design by Larsson will give you all the math you need.
Good grief...it’s a fast catamaran not the polar icebreaker the manatees require to carry their beer and pizza bazooka.
You and SMJ will sail circles around us, but we can fend off krakens, orcas and hungry ice bears.
Happy fabrication. Keep it simple.
Captain Mark and the manatee crew.

[MicHughV]

Years ago, I built a Bruce Roberts boat. I ordered the plans, and a pretty large roll of plans and a "how to" booklet was delivered to me.

The plans gave the basic outline of how to construct the boat, and the booklet some "typical" details, but assumed "correctly" in my opinion, that the builder would likely change many things to suit his/her needs. The boat could be built in hard chine steel, fiberglass, right side up, upside down, etc....it was up to you, the builder to decide.

The plans did not...and could not give specific details for everything. An easy example would be engine selection, hull thickness, interior layout, etc, etc.....these are all basically up the builder building the boat. There was someone available to answer specific questions, but the builder was dependent on his/her own interpretation of how something should be built.

I go with manateeman here. To date, you have proved yourself to be a resourceful person. This chainplate issue is clearly a dilemma for you. I don't think you are seeking a nuts and bolts answer, but guidance, and really the NA is the best person to do so.

I would imagine that building this cat would follow in a similar manner as outlined above. The designer does not know how, where or when you plan to build the boat, anymore than any CF member does. The designer does not know your skill level, size of pocket book, and a myriad of other details or whether you plan on following his design to the n th degree.

I can imagine that a designer would be inundated with questions from builders, building his designs, to the point where he would get nothing done. He sold you the plans, he did not sell, daily, weekly or monthly consultation meetings with anyone to discuss the many issues any builder is likely to come across.

Not standing up for the lack of correspondence from the NA, but trying to explain, what is the typical procedure here for a home builder.

I see no need to stick to this design for the chainplates, if you don't want to. If you want to put the chainplates on the outside, you are free to to do so.

I think it's impossible for anyone here to give you a perfect answer, as we do not know the boat, have never seen it, don't know the construction details, don't know the location, don't know the rigging size, don't know the loads, etc, etc. It's really up to you to decide what you want to do. I suspect that this chainplate is not typical either and that other chainplates might be different depending on their location and specific requirements.

I've come to learn that there are a number of very smart, experienced, technically competent people on this forum who are willing to throw their 2c in the pot, just like me. But we don't even know the basic dimensions of this chainplate, nor do we know the composition of the hull at this point..

This is a long response, it's just time to take a deep breath and look at this issue piece by piece, bit by bit.

[Chotu]

Originally Posted by MicHughV

Years ago, I built a Bruce Roberts boat. I ordered the plans, and a pretty large roll of plans and a "how to" booklet was delivered to me.

The plans gave the basic outline of how to construct the boat, and the booklet some "typical" details, but assumed "correctly" in my opinion, that the builder would likely change many things to suit his/her needs. The boat could be built in hard chine steel, fiberglass, right side up, upside down, etc....it was up to you, the builder to decide.

The plans did not...and could not give specific details for everything. An easy example would be engine selection, hull thickness, interior layout, etc, etc.....these are all basically up the builder building the boat. There was someone available to answer specific questions, but the builder was dependent on his/her own interpretation of how something should be built.

I go with manateeman here. To date, you have proved yourself to be a resourceful person. This chainplate issue is clearly a dilemma for you. I don't think you are seeking a nuts and bolts answer, but guidance, and really the NA is the best person to do so.

I would imagine that building this cat would follow in a similar manner as outlined above. The designer does not know how, where or when you plan to build the boat, anymore than any CF member does. The designer does not know your skill level, size of pocket book, and a myriad of other details or whether you plan on following his design to the n th degree.

I can imagine that a designer would be inundated with questions from builders, building his designs, to the point where he would get nothing done. He sold you the plans, he did not sell, daily, weekly or monthly consultation meetings with anyone to discuss the many issues any builder is likely to come across.

Not standing up for the lack of correspondence from the NA, but trying to explain, what is the typical procedure here for a home builder.

I see no need to stick to this design for the chainplates, if you don't want to. If you want to put the chainplates on the outside, you are free to to do so.

I think it's impossible for anyone here to give you a perfect answer, as we do not know the boat, have never seen it, don't know the construction details, don't know the location, don't know the rigging size, don't know the loads, etc, etc. It's really up to you to decide what you want to do. I suspect that this chainplate is not typical either and that other chainplates might be different depending on their location and specific requirements.

I've come to learn that there are a number of very smart, experienced, technically competent people on this forum who are willing to throw their 2c in the pot, just like me. But we don't even know the basic dimensions of this chainplate, nor do we know the composition of the hull at this point..

This is a long response, it's just time to take a deep breath and look at this issue piece by piece, bit by bit.

That’s a good post. And I really like what manateeman said also. I like the idea of simplicity, and I certainly don’t mind seeing the chain plates. I think chain plates look nice on a boat. As long as they’re not made out of I-beams. Ha ha ha.

That’s our running joke.

You mentioned that you don’t know the boats dimensions. Let me attach them to this post again. I had posted them in a different thread. I can put the entire rig dimension right here in this thread.

The numbers you have to know are the boat weighs a maximum of 20,000 pounds. That is an over estimate. If I do the most horrible job, it might get close to that. In reality, it’s significantly lighter than that.

The beam is 25 feet. That’s the other piece of data you need to know. That’s how the righting moment is calculated.

Now, you wanted rig dimensions? Here they are.

Please excuse the messy drawing, but that was just for my personal use. I didn’t make it for others. All the numbers are in inches. Unless otherwise noted.

Also, I would love a nuts and bolts solution. If anybody knows how to do a chain plate in easy way given these dimensions, and the weight of the boat, and the beam of the boat, I would be ecstatic.

Like manatee man said, it’s not rocket science. It’s pretty easy actually. But I definitely don’t want to get it wrong.

[fourlyons]

Originally Posted by Chotu

Well, maybe. That really wasn’t the focus of the thread. I was trying to indulge RSlifkin.

My understanding is the force on the chain plate is the righting moment of the boat. That’s it. How could it be anything else? What is holding the boat down to the water? Gravity. When you grab onto the top of the mast, and you start to pull the boat over, the force you are exerting at the top of the mast is what goes into the chain plate. No?

We are not talking about light wind situation here. I think you’re getting confused actually. There is no 1 knot condition. There is also no 100 knot condition with sails up because the boat is already capsized. We’re talking about necessary strength of the chain plate. That is only the condition where the righting moment is exceeded. The case where the boat capsizes. That’s the most force there is on the boat, unless you tie it to the ground somehow. Or anchor it down. It’s just going to tip over.

Where am I wrong about that?

You are correct Chotu, it is righting moment, not sail area or wind strength that determines rig loads. Very strong gusts (and sea state) can deliver shock loads that exceed those of the righting moment, but that is one of the reasons for a 3x safety factor.

[Pauls]

I second Manatee's post. This design is poor. It is complex, prone to leakage (which will eventually cause failure), and it is structurally inefficient. An exterior chainplate, for the same strength, will be lighter. It will also be much simpler to build, cheaper, and inspectable.

[Chotu]

Originally Posted by Manateeman

We don’t care who the designer is or how many catamarans he has done but this has got to be one of the silliest chainplates we seen in a long time.
Needlessly complex. Looks prone to leaks, difficult to inspect.
Have your assistant laminate some nice triaxial in epoxy inside the hull. Keep the entire chainplate on the exterior of the hull. Use a backing plate on the interior.
Bolt through with button head bolts and extra heavy nuts inside. Slather it in 5200. If you want a larger surface area for your toggle bolts, double up the top portion of the chainplates and have them welded. We have built silicon bronze chainplates on a glass epoxy hull and you could lift the boat with them. You want high tech bling go titanium. We just see too many too small too complex too hidden too close itty bitty fastenings.
But then again, we like big thick ugly industrial I beams.
This is not rocket science.
Chainplates simply spread the load but the hull must be reinforced. They belong on the exterior of the hull unless the hull is welded.
Look at older wood boats. They did not concentrate the load. Keep the fastenings where you can see them on the interior where you can check them. Simple. Strong. Bolted. Spaced to spread the load.
Principals of Yacht Design by Larsson will give you all the math you need.
Good grief...it’s a fast catamaran not the polar icebreaker the manatees require to carry their beer and pizza bazooka.
You and SMJ will sail circles around us, but we can fend off krakens, orcas and hungry ice bears.
Happy fabrication. Keep it simple.
Captain Mark and the manatee crew.

This is a great post also. Thank you. I would love to follow this type of path. I just need to get some specifics about it. I don’t want to make any mistakes.

Given what you are saying, would I just use the same pattern he did? The same shape? Where should I get my industrial I-beams from? Is there a good place to order them?

And it looks like you’re going to have to lead the way on the polar expedition. SMJ and I will follow up behind. If I build the right chain plate, maybe I can handle Chotulu.

I will put the Larsson book on my list right now. But I also really need to get moving on this chain plate stuff. It’s going to derail the project and the timeline. And cost me another year of having to work on this thing.

I really want to just go simple, fast, all the hardware in front of me. External chain plates. I just don’t know how much of all of that to use.

[dkenny64]

dumb question.. is this being over thought?
why?
ok layer up the glass a foot around the chain plate to say an inch thick.. use 1/2 plates outside and 1/4 plates inside.. 4 maybe 5 1/2 bolts...the 1/2 plates are external to the hull. the 1/4inch are inside the 1" thick fiberglass and tapers to the normal hull about 12" from center..
chain plates that are external are easier to monitor.. those glassed into the hull.. may be on the edge of failing but without xrays..you'll not know until they fail.
for length think 24 to 30 inches on the chain plate..
use 5200 between the external plate and the hull


just a thought
-dkenny64

[Chotu]

Originally Posted by Pauls

I second Manatee's post. This design is poor. It is complex, prone to leakage (which will eventually cause failure), and it is structurally inefficient. An exterior chainplate, for the same strength, will be lighter. It will also be much simpler to build, cheaper, and inspectable.

Who am I to argue with perfect logic? You guys are all right. I agree completely. I think manateeman’s idea is the way to go.

I just need some scantlings on it. So that I can make sure I don’t underdo it or overdo it. I also don’t want it too heavy if I can help that. But I do want an adequate to hold up to the 3x loading fourlyons has helped to teach about on this thread.

One more for McHughV: the hull is as follows...

36oz triax/1”thick, 6lbs corecell/ 36oz triax

Locally in the area of the chain plates, it is done much higher density corecell that feels like wood. It’s like 12lb or 16lb or something. I don’t recall. I could check if necessary.

All is resin infused epoxy construction.

[Chotu]

Originally Posted by dkenny64

dumb question.. is this being over thought?
why?
ok layer up the glass a foot around the chain plate to say an inch thick.. use 1/2 plates outside and 1/4 plates inside.. 4 maybe 5 1/2 bolts...the 1/2 plates are external to the hull. the 1/4inch are inside the 1" thick fiberglass and tapers to the normal hull about 12" from center..
chain plates that are external are easier to monitor.. those glassed into the hull.. may be on the edge of failing but without xrays..you'll not know until they fail.
for length think 24 to 30 inches on the chain plate..
use 5200 between the external plate and the hull


just a thought
-dkenny64

I think it is being over thought. By me.

And this is actually what I thought the plans said at first. Although they do say internal, I was going to reverse them and put the chain plate outside. And I expected to see a backing plate inside or at least on the other side from wherever the chain plate was located. When I didn’t see that, that’s when I started the thread. Because I got very confused.

This is basically exactly what I want to do. And I don’t want plywood involved. That’s what bothered me also about his design. I’ve had no shortage of rot on my boat anywhere I decided to stick a piece of plywood.

What would be the width of the chain plate you are proposing?

Are you thinking a regular strap? Or something that gets wider?

[fourlyons]

Originally Posted by Chotu

This is a great post also. Thank you. I would love to follow this type of path. I just need to get some specifics about it. I don’t want to make any mistakes.



Given what you are saying, would I just use the same pattern he did? The same shape? Where should I get my industrial I-beams from? Is there a good place to order them?



And it looks like you’re going to have to lead the way on the polar expedition. SMJ and I will follow up behind. If I build the right chain plate, maybe I can handle Chotulu.



I will put the Larsson book on my list right now. But I also really need to get moving on this chain plate stuff. It’s going to derail the project and the timeline. And cost me another year of having to work on this thing.



I really want to just go simple, fast, all the hardware in front of me. External chain plates. I just don’t know how much of all of that to use.

It sounds like you already have the chain plates made, why not install them on the exterior as drawn. But don't embed the bolts, bring them right through the hull. The interior install didn't require backing plates, why would exterior? But if it makes you nervous, install backing plates.

[Chotu]

Basically, this is really frightening. I’ve done a lot of work on this boat as you guys know against incredible odds. More odds than most people face. This is an extremely important part of the boat. If it fails, people can get hurt, die, it will destroy my rig, it will destroy other parts of the boat. So I am scared. I will admit it. I am frightened. I just want to get this right. And my plans are of almost no help.

[Chotu]

Originally Posted by fourlyons

It sounds like you already have the chain plates made, why not install them on the exterior as drawn. But don't embed the bolts, bring them right through the hull. The interior install didn't require backing plates, why would exterior? But if it makes you nervous, install backing plates.

Actually, the chain plates got made by mistake. I asked a friend to ask a friend about them. And instead of giving me a quote, they made them out of 304 stainless. And I have no idea how they figured the plans out because I don’t know what they were supposed to be. I’m not sure how the fabricator knew.

Anyway, I was not able to take 304 chain plates, so they got used for something else. Right now they are supposed to start the new ones. But here I am stuck.

I guess I just wish I had a plan to follow. Something that was definitely going to work. I don’t seem to have that. The only one I have that would definitely work are the composite chain plates. And I don’t think I have the capability to get those done with my help.

And I guess the reason that it doesn’t require a backing plate in the original drawing is that the deck is taking up the transverse load isn’t it? If I put the external, the transverse load goes right into the chain plate. So that will pull on the bolts in a direction normal to the surface of the hull. That’s different than the way he designed it. The way he designed it, the deck took care of that.

So this is pretty tricky stuff. And I don’t know what I’m doing really. Just enough to be dangerous as they say.

[Chotu]

McHughV: you’re right though. I owe some Heinekens. To everyone that helped in a significant way on the forum during the build.

I will take anyone who helped in a significant way out for a few hours as a token of appreciation if they want to sail such a beast as I’m trying to get done here.

It’s a fairly uncommon boat, so it may be interesting to some.

[rslifkin]

Originally Posted by Chotu

Basically, this is really frightening. I’ve done a lot of work on this boat as you guys know against incredible odds. More odds than most people face. This is an extremely important part of the boat. If it fails, people can get hurt, die, it will destroy my rig, it will destroy other parts of the boat. So I am scared. I will admit it. I am frightened. I just want to get this right. And my plans are of almost no help.

If in doubt, either overbuild them, or talk to a rigger about what options would be strong enough. Then you just have to worry about the hull buildup for strength, but it seems like that part is more clear from the plans.

It's definitely one of those places where I wouldn't try to optimize, but would go for "definitely strong enough even if I got it a bit wrong"