Would anyone be willing to help me interpret chainplate plans?

[MicHughV]

Chotu,

You can only eat the elephant one bite at a time.

A sailboat rig is a very complicated thing. Everything must be done right, installed right, tuned right, etc. It must all work in harmony with each other.

I tried to attach a pdf for you, but it's too big, so try this:
Read it thoroughly, several time if necessary.
Let me know if you are able to open it.

HINTS AND ADVICE - Seldénhttps://support.seldenmast.com › files

[MicHughV]

try this instead...

Rigging instructions & sailmakers guide : Seldén Mast ABhttps://support.seldenmast.com › technical_info › riggin...

[MicHughV]

Besides the link I have provided, I've attached a basic sketch for you. This illustrates that the tang should optimally be in line with the shroud. This is to ensure that the turnbuckle pin is flush with the hole in the tang, so that the pin bears along the entire surface of the hole in the tang. If this is not 100% flush, you might want to consider a toggle here.
So this is the first thing to address with your chainplate fabrication.
The second thing is you'll note that the shroud is angled inward, so there will be quite a bit of sideways pressure on the hull, if the chainplate is on the outside. If the chainplate is on the inside, coming thru' the deck, then different loads would apply. That pressure needs to be distributed.
Then off course, there is the whole upward load.
The way that your chainplate is shown in the pics you provided....ie, in two pieces, suggests that it was designed to go inside the boat. To use external chainplates would require a different setup, ie, a single piece.

I (and every one else here) really don't know how your boat is built or designed, or whether you followed the design specs, etc, especially in the area of the chainplate. I also don't know how many spreaders you have, how many shrouds, etc, etc. I do know you have a very tall stick. As before, we can give suggestions, ideas, etc, but this is a major structural component, and I, for one, am not willing to provide anymore detail, as this would be way too complicated without knowing a whole lot more.

At the end of the day, my advice remains the same. Consult with the NA, however difficult this may be for you. Tell him, your preference is to have the chainplates on the outside for construction and inspection purposes. He may or may not agree, but he is the one to ask. If you go outside, I'm pretty sure, he'll have to give you a different design and probably charge you for it.

That's how I see this situation.

[Chotu]

Originally Posted by MicHughV

Besides the link I have provided, I've attached a basic sketch for you. This illustrates that the tang should optimally be in line with the shroud. This is to ensure that the turnbuckle pin is flush with the hole in the tang, so that the pin bears along the entire surface of the hole in the tang. If this is not 100% flush, you might want to consider a toggle here.
So this is the first thing to address with your chainplate fabrication.
The second thing is you'll note that the shroud is angled inward, so there will be quite a bit of sideways pressure on the hull, if the chainplate is on the outside. If the chainplate is on the inside, coming thru' the deck, then different loads would apply. That pressure needs to be distributed.
Then off course, there is the whole upward load.
The way that your chainplate is shown in the pics you provided....ie, in two pieces, suggests that it was designed to go inside the boat. To use external chainplates would require a different setup, ie, a single piece.

I (and every one else here) really don't know how your boat is built or designed, or whether you followed the design specs, etc, especially in the area of the chainplate. I also don't know how many spreaders you have, how many shrouds, etc, etc. I do know you have a very tall stick. As before, we can give suggestions, ideas, etc, but this is a major structural component, and I, for one, am not willing to provide anymore detail, as this would be way too complicated without knowing a whole lot more.

At the end of the day, my advice remains the same. Consult with the NA, however difficult this may be for you. Tell him, your preference is to have the chainplates on the outside for construction and inspection purposes. He may or may not agree, but he is the one to ask. If you go outside, I'm pretty sure, he'll have to give you a different design and probably charge you for it.

That's how I see this situation.

McHughV, I gave you all the information about the boat.. It’s a fractional rig. Standard Catamaran rig. Double diamond. I gave you all the rig dimensions. I gave you all the dimensions of the hull. I gave you the complete construction information for the hull. I gave you the weight of the boat. What else is there?

I’m not sure why you’re saying you don’t have this information.

I made a post with all of this information.

Post number 49 and post number 54 contain everything you have asked for. And a complete an absolute description of the entire boat.

https://www.cruisersforum.com/forums...ml#post3592518

https://www.cruisersforum.com/forums...ml#post3592524

Those two posts contain a complete description of this boat and its rigging. Further, we have a design for the chain plates right here in the first post of the thread. What is missing? Tell me.

[Chotu]

I’ll look at some external plates to see about the part that needs to be inline.

[Chotu]

You know, these metal chain plates are just too hard.

Maybe I should just go with the composite ones after all.

I’ll see if I can organize that. At least I know they will work.

I just wish I could do them with vinylester somehow. Then the lamination would definitely be good since I could do the work with my helper.

[MicHughV]

Chotu,

This is where I see the problem with having this particular chainplate on the "outside"...see attached sketch.

There will be a 1/4" space between the tang and hull (the thickness of the chainplate). That tang will likely get pulled towards the hull and crack the hull.

If the chainplate is to go on the outside, it should be a different design.

Not trying to frustrate you, trying to help you.

[Chotu]

Originally Posted by MicHughV

Chotu,

This is where I see the problem with having this particular chainplate on the "outside"...see attached sketch.

There will be a 1/4" space between the tang and hull (the thickness of the chainplate). That tang will likely get pulled towards the hull and crack the hull.

If the chainplate is to go on the outside, it should be a different design.

Not trying to frustrate you, trying to help you.

Definitely. I hadn’t even considered doing what you drew. That would be terrible. I agree.

If it were outside, it would just be a straight half inch chain plate.

BUT.... the transverse force on the chain plate would move it like my red arrows show. It would try to pull out of the hull at an angle normal to the hull too. As well as the usual chainplate pull.

So... the design the designer did wouldn’t work. Those screws without backing plate would rip right out. It would need a backing plate.

Incidentally, this would weigh 3x what the designer’s design does.

[Chotu]

I’m very frustrated actually because I need to start the chainplates TODAY.

I have a metal guy waiting on me, I have hot weather approaching, Marina said I can’t store my rig on land here any more, I have a deadline to leave, I’ll have an idle employee in 2 days, etc etc

I can’t waste any more time.

I need to start building chainplates immediately.

Before starting this thread, the lamination work was starting for the chainplates tomorrow. The metal work would have started yesterday.

This boat needs to get done!

I needed help interpreting the plans. Now it’s another redesign. I honestly am really struggling here.

[smj]

Consult another multihull NA? Maybe try Richard Woods? I believe he’s still in the consulting business and seems to design with common sense.

[Lodesman]

Originally Posted by Chotu

Definitely. I hadn’t even considered doing what you drew. That would be terrible. I agree.

If it were outside, it would just be a straight half inch chain plate.

BUT.... the transverse force on the chain plate would move it like my red arrows show. It would try to pull out of the hull at an angle normal to the hull too. As well as the usual chainplate pull.

So... the design the designer did wouldn’t work. Those screws without backing plate would rip right out. It would need a backing plate.

Incidentally, this would weigh 3x what the designer’s design does.

Why would you not keep the 1/4 "support plate" glassed in on the inside of the hull, with the chainplate thru-bolted? I would radius the chainplate around the rounded part of the gunwhale.

[Chotu]

Originally Posted by Lodesman

Why would you not keep the 1/4 "support plate" glassed in on the inside of the hull, with the chainplate thru-bolted? I would radius the chainplate around the rounded part of the gunwhale.

Hmmm. That’s not a bad idea, really.

I could even lengthen the chainplate so it was able to bolt to more of the support plate to help with that transverse load.

Only thing then is the tendency for the external chain plate to move. For the through bolts to drag through the hull as the shroud pulls it vertically. There would be nothing resisting that motion, right?

Or would the support plate resist that motion transferred through the bolts, so long as the core doesn’t crush?

[Chotu]

Originally Posted by smj

Consult another multihull NA? Maybe try Richard Woods? I believe he’s still in the consulting business and seems to design with common sense.

Maybe. That’s a long process. I need to get this moving now, unfortunately. I’m backed into a corner. My employee is idle today because of this.

[rslifkin]

Originally Posted by Chotu

Hmmm. That’s not a bad idea, really.

I could even lengthen the chainplate so it was able to bolt to more of the support plate to help with that transverse load.

Only thing then is the tendency for the external chain plate to move. For the through bolts to drag through the hull as the shroud pulls it vertically. There would be nothing resisting that motion, right?

Or would the support plate resist that motion transferred through the bolts, so long as the core doesn’t crush?

As long as the bolts are tightened sufficiently, vertical movement shouldn't be a problem. I've never heard of it as an issue on any of the (many) boats that use external strap type chain plates through bolted with a backing plate.

[Chotu]

Originally Posted by rslifkin

As long as the bolts are tightened sufficiently, vertical movement shouldn't be a problem. I've never heard of it as an issue on any of the (many) boats that use external strap type chain plates through bolted with a backing plate.

Yeah. I think this might be it. I was really heading down the road toward the composite chain plates again, but, this has real potential.

The question about these bolts being tightened sufficiently is how tight is sufficient? Because, I’m sure I could definitely crush the core if I tighten it up to some huge torque.

I was picturing something like this where the blue is the external chain plate, the black are bolts and the support plate (exactly as in the designer’s plans) is inside the boat. With plywood and epoxy plugs and everything.

Only thing missing here would be the millions of bolts he has that go through to the skin of the boat outside. Would I still do those?

Maybe doing the holes for the connecting bolts so they have a huge annulus of epoxy would get rid of the crushing factor?

Or even decoring the whole strap area, putting in 1/4” of glass and bolting through that to the “support plate” inside the boat?

I’m kind of curious why he has all the plywood layers inside the boat holding the support plate anyway. Is it possible to just spread that load using larger sheets of glass below the support plate?

Edit:

I understand why he has the plywood now. It’s for those epoxy plugs. As you pull on them along the surface of the hull, the plywood picks up that pull and transfers it to the glass which then transfers it to the hull.