Moving Rear Chainplate External

Thursty30 · Jul 6, 2017

I am finishing up the drawings for my rear chainplate, the ones for shrouds and fore stay are already in fabrication using tried and tested designs (from this forum) and simply duplicating the bow plate. My question is whether the external chain plate needs to be as long as the one that is buried in the transom.

With my design for the aft plate, I am going to drill through the old plate that will remain bedded in the transom (picture 3) and use 3/8'' SS bolts, much like the sides. Can I shorten the length of the new external plate & use 3-4 bolts, instead of spanning the full 15'' and using 8? The full 15'' rod with anchor will be re-glassed, and in my mind bear most of the forces pulling up. The less holes I drill through that the better, right?

If the pictures don't clarify my intent, or I haven't explained my self well let me know.

Thanks,

Conrad

footrope · Jul 11, 2017

A few questions

Are their any fasteners in the transom for the old plate? I don't see any, and you mentioned drilling, but want to make sure. Is the plate in the transom secure and what is the corrosion like in the areas you can see? Do you have any idea what the forestay-back stay tension is set to? Is this a 30 foot boat?

Thursty30 · Jul 12, 2017

footrope said:
Are their any fasteners in the transom for the old plate? I don't see any, and you mentioned drilling, but want to make sure. Is the plate in the transom secure and what is the corrosion like in the areas you can see? Do you have any idea what the forestay-back stay tension is set to? Is this a 30 foot boat?

This is the E-29 model (~28.6'), I do not know what the tension is set too for the stays. There are no fasteners in the existing aft plate, I will be drilling for the new fasteners, I ended up with a design that uses (7) 3/8 bolts over 15'' of 1/4'' 316SS for what will be the new exterior mounted chain plate. The plate in the transom is secure, no corrosion visible that I can see. The section that I carved out to expose the bottom (pictures above) was bone dry, as has been every other part of the boat that I cut into so far. With the exception of the aft lower staboard chainplate, it was obviously not bedded properly where it comes through the deck and so water was able to penetrate there.

What are your concerns? I have submitted the designs to my metal fabricator and will get pricing tomorrow, so there is still time to make modifications. Interested in your thoughts.

Thanks,

Conrad

footrope · Jul 12, 2017

Hi Conrad,
If you're replacing 1/4" with 1/4" then I think you have a pretty good plan. Seven bolts sounds better than five to me. I was trying to figure out if you were changing to external to avoid problems or to fix an existing issue that had developed with the old one. Also the size of your boat, plus wire and pin size is a rough guide to the strength needed when you tension the rig. But I'm not applying any actual science to this, just common sense comparisons of the new to the old.

You have the potential to introduce moisture all along the length of the old chainplate with the plan to tie into it. So do a good job of sealing it up.

Loren Beach · Jul 12, 2017

Six is a nice round number

Picture of ours in reply #3 in this thread.
http://www.ericsonyachts.org/infoexchange/showthread.php?7890-Transom-Thru-Hull-Replacement

I would guess that using your old glassed-in section for a backer should work great.
Six large ss bolts work for our boat, and should be strong enough for yours.
(Just my SWAG... but I am not an engineer.)

Thursty30 · Jul 13, 2017

Footnote - I have tried to let common sense be my guide, everything I do is intended to be as good/better then what I am replacing. Also adding backing plates (which in turn reinforces the hull deck joint) behind all new chain plates to give thick flat sections for the bolts to penetrate. Appreciate the feedback, very good point about introducing moisture. I don't want to ream out the steel wide enough to seal the penetration with epoxy, so I will likely end up using mainsail methods and his bed-it tape. The stuff worked unbelievably well for rebedding my portlights to the cabin.

Loren - Thanks for the input. My finished product will be similar, so happy to see I am not reinventing the wheel. I don't like being a guinea pig with these types of projects. I just did added a couple above the water line thru hulls (increased scuppers from 3/4'' - 2'', and moved above water line). Fought the same battles you did, ended up using a pipe wrench to turn the nuts on the large through hulls. I was a little frustrated and tired after being crammed into the tiny lazarette fighting those fittings all day, so I didn't take any after pictures. I'll have to snap some this weekend.

toddster · Jul 13, 2017

Tangentially related, but last night I came across photos of an E29 that has had the lowers moved inboard and more fore-and-aft. I think I had seen pictures of this same boat before and couldn't quite figure out what was going on with it. I wonder who did this and what the thought processes were? Maybe easier to walk down the side decks, but is it structurally sound? Looks like they went with a split backstay and left the old chainplate in place.