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post #1 of 12 Old 10-10-2014 Thread Starter
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Funky funky chainplate puzzle

That is, the original chainplates on our Albin Ballad 30'er were funky, and I'm puzzled how to approach the aft lowers. None of the (inboard) shrouds happen to align with interior bulkheads, so Albin went to some trouble building trusses and weldments that did attach to bulkheads, and then used shouldered eye bolts for the thru-deck hardware.

We're reusing the original trusses with new eyebolts for the forward lower and upper shrouds. No problem. But our Ballad had pilot berths outboard of the settees, so the aft lower chainplates sorta bolted thru the cabinetry & went thru doubtful gyrations before tying into a species of half bulkhead tabbed to the hull:

chain1
chain2

Well, we've done away with the pilot berths and sistered lovely 3/4" Hydrotek to the old half bulkheads, bringing us right up to the side decks.

portside

Whatever chainplate we attach to THAT is going to be much stronger than original. Issue is, the new plywood makes reusing the original welded thing (with eyebolt) problematic, as we would need to turn it 90 degrees & that means top is the wrong angle. And using it would move the eyebolt forward a little, about 3/4" from its original location. Furthermore, we'd still need to extend the welded thing down another 15" or so if we want to bolt it all the way to the hull, including thru the old half bulkhead.

Alternative: Ordinary flat SS chainplate (1.25"x3/16"x36") for the aft shrouds, which puts us almost in the right location, saves a couple eyebolts, and runs uninterrupted from toggle pin to hull.

Could also have a machine shop cut angled thing & weld a new top on it.

What is your advice? Figure out a way to adapt the old bracket & use an eyebolt? Or just employ a conventional flat chainplate for the aft lowers?

Buccaneer18, Grainnia
SJ21, Diarmuid
Albin Ballad 30, Fionn
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post #2 of 12 Old 10-10-2014
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Re: Funky funky chainplate puzzle

Maybe use flat SS bar but try to prebend/twist the above deck portion to better align with the angle of the aft shroud?

Or, alternatively, use the flat bar but have your machineshop/welder fabricate a piece to weld to the top of it that provides the angles, as well as greater surface area for sealant.

Ron

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".. there is much you could do at sea with common sense.. and very little you could do without it.."
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Re: Funky funky chainplate puzzle

Consider to use straight bar-stock for your chainplate - no bends, no kinks, nor 'twists' (are 'stress risers' that make the metal less strong and promote fatigue cracking), no welds (heat affected zone weakens the metal). Just a straight piece of bar stock.

Beneteau uses rod stock ... and a simple T connection to the hull, no multi-drillings to a knee, etc. Pure stress connection without 'adulterations' - pure, simple, brilliant.

Put a high 'mirror polish' on those chainplate to enhance 'fatigue resistance'.
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Re: Funky funky chainplate puzzle

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Originally Posted by Faster View Post
Maybe use flat SS bar but try to prebend/twist the above deck portion to better align with the angle of the aft shroud?

Or, alternatively, use the flat bar but have your machineshop/welder fabricate a piece to weld to the top of it that provides the angles, as well as greater surface area for sealant.
My welder is only a hypothetical welder at this point, but that is a possibility. Approximate angles on the lower shrouds are 9 degrees inward (more than covered by the bulkhead angle) and 6 degrees fore&aft. which we will probably obtain thru a bend in the chainplate. An eyebolt, of course, would have no trouble with that much offset -- just aim it toward the mast. I'm thinking we would start the bend below decks & angle the slot thru the deck, to minimize stress concentration of a bend at deck level. Dunno?

Nice thing is we can get 36" lengths of 316SS for, like, $17 each. Polish them pretty. If Greg/Stumble wants to woo me with titanium, I'm listening. Cuz one downside to the flat bar vs. eye bolts is ease of pulling for inspection every five-ten years.

Relative strength of materials (all 316 or 316L stainless):

1/4" wire: 1,400#WLL; 7000#BL
3/8" clevis pin: 2,400#WLL; 7,700#BL
3/16x1.25" bar (with 3/8" pin allowance): 4,100#WLL; 11,000#BL
1/2" eyebolt: 2,150#WLL; ~9,000#BL (per Suncor)

Since the Ballad originally had 6mm wire, either chainplate solution is likely to be stronger than the wire, which is prolly 2x overkill for the loads. It's not that big of a boat. So it's down to convenience, fabrication cost, and durability going forward.

Buccaneer18, Grainnia
SJ21, Diarmuid
Albin Ballad 30, Fionn

Last edited by bobmcgov; 10-13-2014 at 12:03 PM.
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Re: Funky funky chainplate puzzle

If you are having new stuff made up, why not use the tie rod system - it's well proven. Get a deck tang fitting welded up to suit, have a matched piece for under the deck with an eye in it and a tie rod to connect there and to another eye on the stringer or in the bilge or welded to the mast step if keel stepped.

Makes a tidier and simpler installation than forcing flat bar through all those gyrations.

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Re: Funky funky chainplate puzzle

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Originally Posted by SloopJonB View Post
If you are having new stuff made up, why not use the tie rod system - it's well proven. Get a deck tang fitting welded up to suit, have a matched piece for under the deck with an eye in it and a tie rod to connect there and to another eye on the stringer or in the bilge or welded to the mast step if keel stepped.

Makes a tidier and simpler installation than forcing flat bar through all those gyrations.
It would be a possibility & a good option if we had kept the pilot berths. Tie rods can span those. But the pilot berth is gone, so now we have a really strong bulkhead running right up to the side deck w/in 5/8" of the correct chainplate exit location. My question is whether to find some means to use the 1/2"d eyebolts I bought, or whether to just use flat bar right off the bulkhead. It's aesthetic as much as anything: two eyebolts and a tang looks silly. But also ease of future extraction and inspection. Eyebolts win that one.

I do think it would be handy to bend any flat bar below decks if possible, to reduce the chances of fatigue and corrosion of a bend at deck level. We're only talking about 6* or so.

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Re: Funky funky chainplate puzzle

Pics! Here is where the bulkhead meets the side deck, with the cross showing where (at deck level) the chainplate eye has to land:

chain1

By some crazy chance, that cross falls right in the middle of a 4x4x1" chunk of phenolic core replacement.

Our two competing options:

chain2

Foreground is a mockup of a flat bar chainplate, bent 6 degrees below deck level. The real thing would be 316LSS, 1/4"t x 1.25"w x 36" long.

Background is the original strut with 1/2" shouldered eyebolt.

Original strut in place:

chain3

The bolt ends up a titch forward or original location, maybe 1/2", and there's that gap at the top of the strut because we've rotated it 90 degrees. Nothing a blob of thickened epoxy can't remedy.

Flat bar chainplate showing how it would go in:

chain4

It's virtue is its simplicity -- one continuous piece of steel from turnbuckle toggle to hull tabbing. And we hit the design shroud location dead nuts. Also roughly twice as strong as the eyebolt.

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Albin Ballad 30, Fionn
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Re: Funky funky chainplate puzzle

If the eyebolt arrangement was original and satisfactory, it has the advantage of more-or-less being self aligning under load.. Also probably an easier thing to bed/seal esp if you had a SS timber washer welded under eye, and drilling a hole is more straightforward than cutting a slot.

btw... to my eye (in pics, anyway) the tabbing looks a bit lightweight? is it finished?

Ron

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Re: Funky funky chainplate puzzle

Your design looks just fine to me - bolt it through that bulkhead and call it done.

I agree with Faster though - I'd put at least two more layers of glass on all that tabbing

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Re: Funky funky chainplate puzzle

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Originally Posted by SloopJonB View Post
Your design looks just fine to me - bolt it through that bulkhead and call it done.

I agree with Faster though - I'd put at least two more layers of glass on all that tabbing
Which design do you like -- the strut, or the flat bar?

The upper tabbing may get one more layer of tape; it's tabbed both faces & not doing much but keeping the bulkhead located on the side deck. And remember -- there's gonna be a big-ass piece of metal passing thru 1.25" of reinforced deck sandwich right.at.that.spot. The edge compression of the phenolic core is 25,000 psi. Face compression 45,000. Lateral movement seems unlikely.

The real business (load path wise) takes place where that bulkhead joins the hull -- and that is tabbed much more heavily, including 6" wide 18oz biaxial tape. Then the bulkhead gets tied to the settee backs, which are further tabbed to the hull to create longitudinal stringers. Then a top hat stiffener gets run from that intersection down to the keel transition, which is 1" of solid FRP.

First post shows how the original chainplate was attached via offset knee using 4 #8 brass screws to that half bulkhead, which was tabbed to the hull using a single layer of CSM on each face of the plywood. That was it. Our new arrangement is roughly ten times stronger than what came from the factory. I may add one more layer of tape to each side where the bulkhead meets the decks (presently 3 layers 10oz tape each face), but it's not a thing I worry about. The important forces here are vertical.

Buccaneer18, Grainnia
SJ21, Diarmuid
Albin Ballad 30, Fionn
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