Would anyone be willing to help me interpret chainplate plans?

[Chotu]

This might just work. It looks like lodesman has earned his ticket for a free day sail if he is on the East cost after this thing is done.

[rslifkin]

You can spread the load with just about any material you want as long as it's strong enough. Extra fiberglass, plywood, G10 sheets, etc. For avoiding crushing, either a big enough epoxy ring in the holes or sleeving them with something like G10 tube would work. Or de-core and rebuild that whole area as solid glass, but that's likely overkill.

Make sure you have enough material on both sides of the core to spread the load, then with properly prepped holes, you should have no issues with crushing or anything when tightening the bolts down. No need for a bunch of tiny bolts or hiding bolt heads or anything either, the bolts just need to be sized to take the shear load without the help of those knobs (and with appropriate safety factor).

[Matt Johnson]

As a reference - We're six 1/2" bolts for our external 1/2" x 8" x 24" chainplates (the bottom 16" against hull). The backing plate is 1/4" stainless and is 9" x 15".

We are solid laminate in this area, but in other high load areas have used the equivalent of Coosa Board 26lb density as plywood replacement.

Hopefully this helps with a baseline.

[Rumpi]

Just stop second guessing the designer and build as drawn. The instructions are clear, even if brief. Laminate the required layers on the outside and inside. If needed, grind the inside flat where the oval plate sits, or bend the plate to the hull. Drill holes, fill, redrill, countersink for heads on the outside, bolt on the oval plate. Bend the tang so the upper part is inline with the wire, bolt over the plate with 4 screws. Fair the screwheads with thickened epoxy, add the last fiberglass layers over them, fair and paint. Before bolting the tang relieve the hole it passes trough the hull so that whatever sealant you use there has enough thickness and width to accommodate the movement from differential expansion.

You are not required to understand the designers reasoning or calculations, and in fact you are unable to do so. The chainplate is designed as you see because the limiting factor is the ability of your hull laminate to resit shear and compression from the bolts. Otherwise he could have just specified one single big bolt, as is the case in other parts of your rig. From the corrosion perspective it is absolutely irrelevant if the boltheads are burried under laminate or not, the shanks would still have the same probability. By putting a heavy laminate over the bolts he has actually lessened the chance of water getting in there. Unless you plan to remove and replace the screws on a regular basis at short intervals, it is the better solution.

[MicHughV]

yes, I like the idea as shown on # 75.....I believe there are 8 holes down the centre....I would use every other one, so you have some " space" between the bolts to distribute the bolt load to the hull.
And use the chainplate as a backing plate. maybe 4 thru-bolts around the perimeter (two each side of the tang) just to add strength....in other words the shroud load is distributed to the hull with the 4 bolts in the tang, plus 4 more on the chainplate....it will act as one unit.
I'd get the tang bent to accommodate the angle of the shroud and position the whole thing as low as possible, so just the last 2" or so show above the deck....this way you have more hull to distribute the load..

I think we are getting somewhere...I welcome comment.

[MicHughV]

I was googling catamaran chainplates and came across several varieties such as this...this is on the outside obviously, but would work just as well on the inside with the tang on the outside.

Still would like to see you get the NA blessing on it though....

[Chotu]

Originally Posted by Rumpi

Just stop second guessing the designer and build as drawn. The instructions are clear, even if brief. Laminate the required layers on the outside and inside. If needed, grind the inside flat where the oval plate sits, or bend the plate to the hull. Drill holes, fill, redrill, countersink for heads on the outside, bolt on the oval plate. Bend the tang so the upper part is inline with the wire, bolt over the plate with 4 screws. Fair the screwheads with thickened epoxy, add the last fiberglass layers over them, fair and paint. Before bolting the tang relieve the hole it passes trough the hull so that whatever sealant you use there has enough thickness and width to accommodate the movement from differential expansion.

You are not required to understand the designers reasoning or calculations, and in fact you are unable to do so. The chainplate is designed as you see because the limiting factor is the ability of your hull laminate to resit shear and compression from the bolts. Otherwise he could have just specified one single big bolt, as is the case in other parts of your rig. From the corrosion perspective it is absolutely irrelevant if the boltheads are burried under laminate or not, the shanks would still have the same probability. By putting a heavy laminate over the bolts he has actually lessened the chance of water getting in there. Unless you plan to remove and replace the screws on a regular basis at short intervals, it is the better solution.

OK, I don’t want to derail anything with the other line of conversation, but this post is important. So far, no one here has been able to understand the plans. You are the only one. Can you please stay with this thread and help us figure these plans out? I started this thread because I couldn’t understand what the plans said. Truly, I do want to just build to plan. But I don’t know what they say.

A few questions if you could:

1) In the drawings of the chain plate and support plate, it is very difficult to tell how far up the support plate is supposed to go. Do you have any idea from the plans? Does it go all the way up into the deck lamination?


2) How do the bolts that hold together the chain plate and the support plate work? They are not shown at all in the drawings. Do they go all the way through the hull? Or do they end inside the boat?

3) what exactly is the reinforced deck plate? And how do you install it? What are the specific layers of glass to go there?

4) The hull isn’t flat like you had mentioned. So, how do I put the flat pieces of plywood on there? Do I fill the gap? You talked about grinding, but that takes away the skin and leaves a very thin core left. There would be just core showing after that.

5) to be double and triple clear, there is nothing but some machine screws holding it to the outside of the boat. Correct? Just beef up the glass a little bit like it describes, put in the machine screws, then glass them over? That’s it?


I really wanted to build according to the plan. However, the plan is not even clear enough for anyone on this forum except you to understand it. No one has understood it. Any help you have on helping me understand the plan would be greatly appreciated. Then I can just get to work building this thing today.

[smj]

Our chain plates are 1.5”x15”x3/8” straight stainless (no bends) run through solid glass with 5-1/2”bolts and fender washers, no backing plates. Been there for 21 years with lots of hard racing and no signs of stress.

[Chotu]

Matt and SMJ, thanks for the real life data. That’s actually really helpful for understanding the stuff and making it a lot less scary to deal with.

I must decide today on what to do.

[Chotu]

Originally Posted by MicHughV

yes, I like the idea as shown on # 75.....I believe there are 8 holes down the centre....I would use every other one, so you have some " space" between the bolts to distribute the bolt load to the hull.
And use the chainplate as a backing plate. maybe 4 thru-bolts around the perimeter (two each side of the tang) just to add strength....in other words the shroud load is distributed to the hull with the 4 bolts in the tang, plus 4 more on the chainplate....it will act as one unit.
I'd get the tang bent to accommodate the angle of the shroud and position the whole thing as low as possible, so just the last 2" or so show above the deck....this way you have more hull to distribute the load..

I think we are getting somewhere...I welcome comment.

I welcome some comments on this one also. I definitely want to keep everything running in parallel here so that today I can pick something. I’m still keeping the composite chain plates running in parallel also.

[Lodesman]

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?

I think the point of the support plate is to be glassed in and essentially part of the hull - the large holes are there for the composite to anchor it against the shearing forces imo. I think I would do as rslifkin suggested and de-core that area and build it up in solid glass with the embedded support plate.

[MicHughV]

I've said this from the beginning...the core has got to go...I agree....regardless of outside or inside attachment...

[MicHughV]

I'm starting to feel like I'm building this boat....can't sleep at night anymore, my mind is grappling with a 1,001 ideas...

[Chotu]

Originally Posted by MicHughV

I'm starting to feel like I'm building this boat....can't sleep at night anymore, my mind is grappling with a 1,001 ideas...

I know the feeling. But nobody else should. Ha ha ha.

The worst part is I’m doing all of these things in parallel. Evaluating the different ideas in this thread, evaluating composite chain plates. Really, the most quick and feasible one is the one I would like to do. And the one that works of course.

Maybe it’s time for a little break for you. I can’t take one, but you sure can. You have certainly earned your ticket for a free day sail on this boat when it’s complete.

I think it would be kind of fun to get everybody that has participated in these threads together and all go out together for a day when it’s nice and windy and see what she can do.

I could have never completed a lot of parts of the boat without you guys and it’s going to be a pretty unique boat to sail. So might be fun!

I tend to bounce between Florida and the northeast based on the weather, so maybe we can plan something soon when everyone has time and the rig is on.

[MicHughV]

Yep, that would be an awesome idea.....would love to see your boat one day. I've sailed on a few cats, but none that big.
Ya, some good guys on this forum, for sure.