exterior chain plate?

[Robert]

I have discovered significant corrosion in the aft stay padeye backing plate on Zephyr (CD 28 #230). Two factors have led me to consider switching from the present design to an exterior, hull-mounted chain plate (which seems to be a very common way to anchor the aft stay). The first factor is that the rust on the backing plate and three support rods---which appear to be just garden variety rebar, as in concrete reinforcing bar!---is fairly extensive and would be difficult to repair without complete removal and replacement. Definitely a major project. The second factor is the padeye design itself. It looks like (to my amateur engineering eye) that the backing plate is being loaded excessively at the rear edge, which puts a lot of strain at the hull-deck joint. With enough corrosion where those rebar rods connect to the backing plate, this could lead to hull-deck separation. This is in fact what alerted me to the problem in the first place---a slight lifting of the teak caprail just behind the padeye.
So my question is, given the correct size chain plate, proper backing plates, and proper alignment, is there any reason that would preclude switching from the padeye to an exterior chain plate arrangement. (Removing the plastic storage alcove gives good access to the inside of the hull in this area.)
Any comments or suggestions will be much appreciated.

Thanks, Robert



rbtfshNOSPAM@yahoo.com

[Will Parker]

Sounds like your backstay might be too tight. You better check the tension. Also, I think exterior chain plates are clearly superior. They don't hide their problems. I believe the Cape Dories would be better boats if they had such, e.g. Pacific Seacraft.
Will
"Jambalaya"
CD30

I have discovered significant corrosion in the aft stay padeye backing plate on Zephyr (CD 28 #230). Two factors have led me to consider switching from the present design to an exterior, hull-mounted chain plate (which seems to be a very common way to anchor the aft stay). The first factor is that the rust on the backing plate and three support rods---which appear to be just garden variety rebar, as in concrete reinforcing bar!---is fairly extensive and would be difficult to repair without complete removal and replacement. Definitely a major project. The second factor is the padeye design itself. It looks like (to my amateur engineering eye) that the backing plate is being loaded excessively at the rear edge, which puts a lot of strain at the hull-deck joint. With enough corrosion where those rebar rods connect to the backing plate, this could lead to hull-deck separation. This is in fact what alerted me to the problem in the first place---a slight lifting of the teak caprail just behind the padeye.
So my question is, given the correct size chain plate, proper backing plates, and proper alignment, is there any reason that would preclude switching from the padeye to an exterior chain plate arrangement. (Removing the plastic storage alcove gives good access to the inside of the hull in this area.)
Any comments or suggestions will be much appreciated.

Thanks, Robert

whildensp@earthlink.net

[CharlieJ]

My 1976 CD28 was a victim of the same design flaw, starting to show strain on the aft deck.
Here's my experience:

#1 removing the old material wasn't that bad....I stuffed old drop cloths on either side to contain the mess. The "secret weapon" after trying various grinding wheels, wire brushes, etc was a very course drill disc sander (like 40 grit as I recall). This really cut into the glass laid over the rotten metal rerod, which just crumbled away. I had to be careful about heat buildup.

#2 the yard mechanic (a very cooperative guy) cut a plate of 1/4" thick 316 SS aprox 6"wide x 10"long to be bolted against the inside of the transom. To the top (6" wide edge) he tack welded a roughly 6" x 6" top plate to fit snugly under the deck under the stay pad eye. We then fitted this "L" in place, carefully bending at the tack weld joint to set the exact angle for a good fit. Then back to the shop to complete that weld and weld on some side tabs. The huge forces are actually traction via these side tabs to the transom plate. The final unit weighed about 20lbs and looked most like a shoe box.

#3 we then working together drilled 5 transom holes in an X pattern and drilled the SS plate for the transom bolts (5/16" I recall) and pad eye bolts.

#4 we smeared bolts and plate with wax, applied a generous area of thick West System on the inside transom, and loosely bolted in the unit.....this gave a solid epoxy base with no stress points. After the epoxy set I took the unit out and "epoxy coated" all the holes. Next day I applied 4200 caulk on all surfaces and holes, and bolted everything back together.

My good fortune was a very helpful yard mechanic. He was happy to have me work with him and my total labor charge was about 3 H. If not for this, an external plate with backing would make more sense.....cutting, drilling, and welding the SS was nothing for him. Major mistake: not converting the shrouds to external chainplates.

[hilbert]

I purchased a 3/8" x 1.5" bar of 316 stainless online, to make an exterior chainplate. It will need to be bent about 45° to have a fair lead.

[CharlieJ]

I had a good time working with John making the internal SS "box", but no doubt the external plate is the simpler, smarter solution. Looks good, too.

[David van den Burgh]

For what it's worth, our '79 CD36 has a similar external chainplate on the backstay. It also has reinforcement fiberglassed to the inside of the transom to spread the chainplate load across a wider area.

I purchased a 3/8" x 1.5" bar of 316 stainless online, to make an exterior chainplate. It will need to be bent about 45° to have a fair lead.