Chain plate questions:

[Chotu]

Originally Posted by rslifkin

I'd prefer wet on wet if possible. At least for the nubs to the outermost layer below them. Probably doesn't matter as much for the plywood bonds.



As long as it can all be done in a day for a single chainplate once everything is prepped, I'd expect a slow enough hardener would allow it to be done wet on wet without any craziness.

That’s true. I think I am leaning toward wet on wet because it is such a crucial piece. This may warrant two people doing the job.

[Benz]

^^ Second the wet-on-wet. It's just that much better to have all your molecules chemically cross-linked.

[Chotu]

OK. Wet on wet it is. That’s my feeling as well. I much prefer things to be properly bonded all in one day.

[Chotu]

Question:

The hull has a slight curvature where the chain plate anchor plate attaches. Very slight, but it exists.

My chainplates look something like tennis rackets. The oval part of the racket is an anchor plate 1/4” thick and the “handle” of the racket is 1/2” thick bar that gets bent a little to line up with the shroud angle.

The oval part of the racket is what’s fastened to the buildup of glass and plywood.

The hull has a slight curve no matter if I do the chainplates internally or externally. I assume the chain plate buildup layers need to grab onto glass right???

Do I need to take down my Epoxy and micro balloons / silica fairing compound on the outside of the boat to dig down to real glass to bond the buildup to? Then what? It’s a little bit of a curve. Still don’t have a clear path to making these in my head and it’s coming up quickly.

Also, internal or external plates?

Internal pros:
Work is easier since there is no standing in a dinghy trying to create the buildup wet on wet.
No chance of dropping hardware or the chain plate in the water.
Less chance of my helper making mistakes to create voids and blow the layup
The plans show the chain plates internal

Internal cons:
A hole in the deck to deal with forever
(Can I just use a rubber boot like masts do and make a lip around the hole to clamp the rubber boot to?)

External pros:
It’s what people want these days
Stainless dries off easily
No hole in deck

External cons
Very difficult install.


Should I just follow the plans here completely and do internal, then rig up a watertight fitting to keep every drop out of the boat rather than play the 1980’s boat game of constantly having to rebed a plate that tries to keep water out of leaky chain plate deck holes?

[Chotu]

I’m really leaning toward just following the plans and doing internal for ease of construction, and I think I have found a foolproof way to keep water out of the deck penetration so there can’t be corrosion from leaks.

[rslifkin]

I'd go with internal being that you're building them with the boat in the water. I'd think if you seal them through the deck with a sufficient amount of sealant that can absorb a little flex and then add a well sealed boot over that it should be easy enough to keep them from leaking.

Just to be on the safe side, make sure the interior design in that area will allow some airflow (and access) to the chainplates and that any water that does get in can drain away without harming the interior. That should minimize any issues if you do end up with a leak at some point.

For the hull curve, I'd think you need to build it up to flat in that spot in one way or another.

[Chotu]

Originally Posted by rslifkin

I'd go with internal being that you're building them with the boat in the water. I'd think if you seal them through the deck with a sufficient amount of sealant that can absorb a little flex and then add a well sealed boot over that it should be easy enough to keep them from leaking.

Just to be on the safe side, make sure the interior design in that area will allow some airflow (and access) to the chainplates and that any water that does get in can drain away without harming the interior. That should minimize any issues if you do end up with a leak at some point.

For the hull curve, I'd think you need to build it up to flat in that spot in one way or another.

OK. I’m pretty glad you agree on where my gut feeling is going here. That’s a good reality check.

I don’t plan to cover the chain plates up at all inside. They are very pretty. They look nice. They are nice beautiful pieces of stainless. I’ll leave them as a decorative item actually. And yes, I’ll make sure to be careful about any drips in that part of the interior so they can’t damage things.

But I think I might have a way to seal these that they never really do on all of the production boats. Shouldn’t be too hard to use a boot.

[Chotu]

Funny. After all of the hashing things around, I’m ending up just going with what the plans say for the whole thing. Ha ha. It’s just easier and more practical to do that given all of the situations that are the world right now.

[drdoyle]

You will need a full size same thickness backing plate for the inside to match the outside chain plate covering the bolt holes as one unit. The backing plate should be wider or narrower than the outside chain plate to prevent a shear point across both sides of the hull. Yes you need to prevent crushing the plywood "core". Either take a router with the correct style bit to cut a slot between the inner and outer fiberglass layers, then fill this with a fiberglass impregnated epoy glue. Or you can machine a anti-crush washer a few millimeters shorter than the hull thickness and epoxy that into the hull bolt holes. The biggest trick is going to be pre aligning the holles to center all the bolt pass-throughs. As an option to routering into the hull a core notch into the bolt hole you culd use a hole saw on the inside and remove only the inside skin and core leaving the outside skin, then epoxy in a large diameter solid SS anticrush fender type washer(s) , then glass the inside to cover all the crush washers (and add strength to the hull). The inside chain plate backer could have an "L" shaped top that would push up against the deck stringer or a deck beam to spead the upforce load partially away from just the hull side shearig forces.

[sailorladd]

The sound of the design of your new chain plates do not make sense.... I replaced all my stainless steel chainplates with a more robust set and basically they are mounted outboard, they use the same bolt-sized holes that run directly through the hull and are cinched tight with "Loctite" with good strong stainless backing plates..... that is very important! Strong wide backing plates...

[Chotu]

Please let this thread die. The executive decision has already been made. Don’t waste your time.

All the materials are on their way to do the composite chain plates. They will be started this coming week.


I liked all the advantages.

With metal, I have 300 different opinions on how to do it and each one says the other will fail. With composite, there’s just one way to do it and it’s very clear.

With metal, I have to worry about corrosion someday. With composite, I never have to look at it again. It’s part of the boat itself.

So, we are going to put in the composite chain plates. Just higher quality than metal. So that’s what I’m going for.

[Jeff H]

As others have pointed out, moving the chainplates to the outside of the hull is not as simple as drilling the right number of bolt holes and bolting the whole thing together. Typically when a boat is designed for external chainplates, there are knees or other types of stiffeners glassed into the interior of the boat that prevent the topsides from flexing. Fiberglass fatigues when exposed to repetitive flexure and without stiffeners there will be flexure, which in turn will weaken the hull.

Friction has nothing to do with how chainplates are attached to the boat. While friction type bolted connections work in steel to steel connections, they have nothing to do with fiberglass construction. The bolts are solely what transfers the loads from the chainplates to the hull. The bolts are in single shear and so try to rotate (heads upward- interior downward).

If passing through a cored hull, (even a plywood cored hull) the bearing surface (shaft) of the bolt needs to be tight against the skins and core. The outer and inner skins need to be thick enough to resist that the bolt trying to saw through and crush the skins. In other words, the big loads are on the skins with the core playing a more minor role.

I agree with the suggestions that the core should be drilled out from the interior leaving the exterior skin intact. I also agree with the suggestion of wetting out the edges of core in the hole and then using thickened epoxy to fill the void. I like the idea of using G10 since that will provide a solid bearing surface.

If I had to do this, I would use a 25mm (1") hole saw to cut out the inner skin and core. I would use the same hole saw to cut the G-10 and make the new G-10 cores. I would rough up all faces of the G-10 with course sandpaper, wet out the edges of the hole, mix up thickened epoxy and use that to fill the voids around the G-10 and hold the G-10 in place.

Once cured, I would grind the surface of interior face of the hull and the G-10 and lay-up multiple laminations of biaxial, cloth, and roving, which ideally will also tie into the new vertical stiffeners.

Only when all that cures would I drill the holes for the bolts.

I will also note that unless this is something like a 25 foot momohull, 1/4" bolts are tiny for this purpose. The issue with bolts that small is that even small amounts of corrosion greatly weaken them as compared to larger diameter bolts where the cross sectional area is proportionately much larger as compared to the surface area.

One of the big issues with external chainplates is accelerated crevice corrosion of the bolts, so the corrosion issue relative to bolt diameter is doubly critical. (By way of comparison, the bolts on the chainplates of my light weight 38 footer are 5/8" diameter, and there are 12 of them per chainplate. The wooden bulkhead they pass through is 1 1/8" thick and has a thickened glass bushing around each bolt hole and sealer laminate if fiberglass glass on the face of the bulkhead. There is also a backing plate that is the same footprint and thickness as the chainplate material.)

Jeff

[Manateeman]

We don’t see how you will get accelerated crevice corrosion if you used silicon bronze plates and bolts.
Not our experience. We could show you bobstay plates right at the waterline so underwater a lot, that look like we put them in yesterday but they are 30 years old. The plates were 2-1/2 x 3/8” and bent to fit the hull and a cross bolt. 1/2” button head bolts with heavy nuts, backing plates and stuck on in 5200.
We did not realize Chotu had a core hull and could not read his drawing in post one. He now has a solution. Our opinion on the advantages of exterior bronze chainplates remains unchanged although they might not be correct for all applications. He has a very high tech, fast and light vessel. Not exactly manatee displacement. LOL. The manatee crew loves to follow these advances high tech Boatbuilding but after beer and pizza expenses, they have little money left.
Happy trails to you.
The manatee crew.