Chainplate Project , hull to chainplate spacer material?

[Kenneth Lawrence Clift]

I have a Pearson Triton 28 made in 1961 I am installing external chainplates and I am wondering what material I can use for a space between the hull and the chain plate it would need to be 1/4" and tapered down to 1/16 ".
I have some good quality Burmese teak and Epe. I have also thought that maybe plastic or nylon shims may be better.
Any help would be appreciated.

 

[fallguy]

Well, just from a materials perspective and not as a sailor, I can tell you I'd avoid taking any wood down to 1/16" and applying pressure to it; even from a caul. It'll crack after all sealed and have a random behavior/seal.

So, if you need to make a spacer, you'll want to avoid going that thin and let the polysulfide do the narrower bits. Can you explain better the need for shimming? It may help others as well.

 

[Rumars]

It's a useless modification especially since you don't have the equipment to mold the chainplates to the hull.

Anyway, in oder of preference:
1. G10 or GP2 bonded to the hull with epoxy and painted.
2. Epoxy thickened with high density filler and milled fibers, painted.
3. Metal, with your sealer of choice.

 

[wet feet]

What makes you believe the alteration is necessary? The boat has lasted 61 years with the original configuration and you would have to achieve a watertight repair to the old fastening holes.

 

[Kenneth Lawrence Clift]

This boat has only been used in semi-protected waters and was not designed for ocean cruising though it has a hull thick enough to survive anything. It was built in 1961 before they knew much about fiberglass and before the invention of chopper guns.
The boat has inboard chainplates that fasten to a bulkhead and a fiberglass stringer. The chainplates are
thin and week-looking. Since the boat will be used for ocean passages we are strengthening everything including new rigging wires, tangs, and mast bolts. The new chainplates need a little more space at the top to accommodate the turnbuckles and I thought a wedge of wood would solve the problem. Epe is very hard and durable. I would bed it in with 3M 4200 black since the hull is black. My main question is would this be acceptable with a boat surveyor from an insurance point of view? The wedges would be 6" x 2" a quarter of an inch at the top tapering to a 1/16" where the chainplate meets the hull. The chain plates are 2" x 18" and 3/16 thick and made of 316L stainless steel. I also intend to connect the 1/8" backing plates into the existing bulkhead chain plates with a piece of 3/16 bent stainless rectangular bar stock.
I would appreciate any further ideas. Thank you.

 

[fallguy]

G10 is okay as Rumars said, wood is not as I said, wood is going to crack on the edges. It is a very simple proposition. Take a piece of wood and taper it from 1/4" to 1/16" and test its ability to withstand any stresses with a simple hand test. If it passes; make another. It simply won't be reliable and will be subject to grain orientation variability in its strength which makes it unpredictable due to the constraints YOU are placing on it; not me.

If you intend to make the boat b/w capable, then you need to engineer the chainplates backing as well. The existing structures may also be insufficient.

If you have such exceptional help as Rumars; I suggest you add some pictures or hire a surveyor with bluewater experience ahead of survey. I paid my surveyor a retainer so I could ask the hard questions.

Again, I'm only telling you wood is a very bad choice based on years of working with many types of wood.

 

[fallguy]

We could carry this exercise out to an engineering analysis to see what the strength of ipe or teak is at 1/16" thick under various grain orientations, but based on my experience; this is not needed.

For a simple comparison, ipe has a compressive strength of about 13,500 psi vs g10 which is about 65,000. This simple comparison says nothing about grain direction. But that G10 is 4 times less likely to crush. I'm less worried about crushing it than cracking the thin end.

If you can avoid taking the timber down to 1/16"; the proposition is more worthy of consideration.

 

[wet feet]

I doubt that the original chainplates would fail under load.It isn't too hard to arrive at a useful figure for the ultimate tensile strength of a piece of 2" X 3/16" stainless steel and it will certainly exceed the entire weight of the boat.The weak points are likely to be the hole(s) for the clevis pins.The simpler solution is to make a longer chainplate of the same material,to allow for the additional clearance you are seeking above deck.Some additional length below deck might allow the addition of another bolt too as the risk of elongating the holes in the bulkheads is probably the greatest weakness of the present setup.It may be that there is a minor risk of the chainplates shearing the clevis pins and this can be reduced by welding on a washer at the correct location and then reaming the hole to suit.An altogether easier project that relocating chainplates to a zone that was never intended to receive or distribute the loads and which would require shaping parts to conform to the shape.But it is your boat and your decision.

 

[Rumars]

Why are you trying to do it the difficult way? If you want stronger chainplates just enlarge and seal the slot in the deck and insert the new ones. The main bulkhead is either sound and strongly attached to the hull in wich case it can take them, or rotten and delaminated needing replacement anyway.
The knees are the same, plywood laminated over with fiberglass, if you want bigger ones (for longer and wider chainplates) you just replace them.

Beefing up chainplates on a Triton is nothing new, the web has examples including pictures. Atom for example has 1/4 x 1.5" 316L plate and 7/32" wire.

 

[Kenneth Lawrence Clift]

Thank you, everyone, for your input. I will certainly go for the G10 method.

 

[fallguy]

Why are you trying to do it the difficult way? If you want stronger chainplates just enlarge and seal the slot in the deck and insert the new ones. The main bulkhead is either sound and strongly attached to the hull in wich case it can take them, or rotten and delaminated needing replacement anyway.
The knees are the same, plywood laminated over with fiberglass, if you want bigger ones (for longer and wider chainplates) you just replace them.

Beefing up chainplates on a Triton is nothing new, the web has examples including pictures. Atom for example has 1/4 x 1.5" 316L plate and 7/32" wire.

My hunch is he wants external plates based on an article in Practical Sailor that lauds the external over internal for the ability to see modes of failure. But the concern for me is whether the new attachments will meet the load requirements. Given that he has not stated the loads; also a small concern.

I know so very little, but I would anticipate the loads for b/w are higher than for inshore or nearshore. So, a change seems prudent.

Assuming the strength of the structure is a fair question, well, I mean an error.

When I installed a simple cleat in my boat I did a load analysis and got help here to verify it.

It would be a wise exercise for him as well.

sorry, beer talking now

 

[wet feet]

My hunch is he wants external plates based on an article in Practical Sailor that lauds the external over internal for the ability to see modes of failure. But the concern for me is whether the new attachments will meet the load requirements. Given that he has not stated the loads; also a small concern.

I know so very little, but I would anticipate the loads for b/w are higher than for inshore or nearshore. So, a change seems prudent.

I would expect the loads in blue water to be exactly the same as in any other kind of water.The duration for which they are present may be greater,because of the distance to and from blue water.I hope our poster has worked out a good way to distribute those loads into the structure because a large and well bonded bulkhead does the job very well.