Installing new chainplates and rotten knee advice needed

[Ben Nicol]

Hi Everyone,

Seeing we are in the spirit of ticking off the big expense items at the moment we have decided go ahead and have the standing rig and chainplates replaced.

We have the mast out and the chain plates off the boat at the moment. Hearing stories of people's drama with the knees I have been poking about in the holes where the chain plates were bolted through. I have found all of the (ply ?) wood core to be sound apart from the lowest hole on the cap shroud chainplate attachment. In this i have found a small amount of the black rot watery goo :(

From the initial inspection it does not appear to go much deeper than about 3cm into the plywood core. I am thinking that we can gouge it out and then fill the hole left from the rot with penetrating epoxy and re-drill the hole.

Has anyone done this before ?
Would anyone recommend this approach or perhaps another ?

Thanks,
Ben

[Ben Nicol]

I should mention that we have a 1988 P40

[psherwood]

3 cm into the core? Or 3 mm? If the latter, I'd be OK with penetrating
epoxy. And I'd seal the rest of the wood with epoxy as well.

Phil

[Ben Nicol]

Hi Phil,

Thanks for coming back to me. This is what they looked like before. It looks original. I'm not sure though. They are glassed in thick and the chain plates are bolted through the knees.

3cm is the depth I believe the rot extends from the edge of the hole outward.

It is very solid and thick glass surrounding it.

[Bill Schmidt]

Ben, looking at your photo, I suspect that someone has already
reinforced those knees. They look too good to be original. I can't see
the chain plates clearly, but they don't look original, The "bad" knees
typically pull away from the hull, starting at the underside of the
deck. Yours look well attached and well faired out onto the hull.

The plywood used was of poor quality and only served as forms for
building up the fiberglass knees. They weren't and are not structural as
far as I know. Another feature of the knees that failed was that the
main shroud knees were made too short using the forms for the fore and
aft knees. Later long forms were correctly used. I'm guessing, from your
photo and the year of manufacture of your boat, that your boat has the
longer knees. If so, I would leave a limber hole to allow drainage of
any leakage, replace the chains (if needed because of corrosion) and
recaulk them back in place.

We had the short knees on Wind Witch; had them redesigned by Tom
Wyle and rebuilt much longer and heavier. We did replace the chain
plates and there was visible corrosion on them at the time. WW was made
in 1983, hull #53. Hope this helps.

Billy Manana

BTW: the worst of the engineering/construction of the chains was at the
stern. Look carefully there. The backing plate was of cheap, common
steel. It rotted away completely and the chain was pulling out of the hull!

[Rob Raymond]

Those look the same as the knees on our 84 P40. I believe they are original.

I wouldn't think the 3 mm of plywood missing inside the hole would effect the structural strength of the knee if that's the only rot you have. Do you still have the teak decks? If so, the cover plate to teak seal will likely be the source of moisture in the knees. It's a good idea to cut the teak away and glass G10 blocks directly to the fiberglass deck where the chain plates come through.

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[Ernie Reuter]

We glassed in G10 plates on Iemanja's refit so that water that entered did not wick past the chain plate areas. Used grey buytl tape to seal up these areas where the chain plate actually comes thru the slot. Has worked very well.

Ernie

SV Iemanja 

Currently...... Vero Beach FL

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[Rick Hurt]

Hi Ben,

Before purchasing my P-40 hull #14, I spent many hours inspecting and surveying her, paying particularly attention to the areas with known issue. Short of pulling out the chainplates, the surveyor and I did all we could to determine if the knees had suffered water intrusion (moisture meter, rapping with survey hammer etc.) . I thought I had dodged the bullet, but the following year when I pulled the plates, I found the stbd knee completely rotten, and the port knee intact. The tabbing connecting the knee to the hull showed no signs of failure. After considering various repair options, a Boatwright friend of mine and I came up with the following repair:

1. cut the nose off the inboard edge of the knee (see pic)
2. thoroughly cleaned and roughed up the interior surface of the knee.
3. cut a new knee core using 3/4" G-10, and epoxied the core in place.
4. roughed up and cleaned the aft side of the knee outboard of the chain plate.
5. Using plywood and epoxy, bonded the aft side of the knee to the adjacent bulkhead.
6. Thu-bolted the chain plates, knee and bulk head together. This required fashioning a removing plywood shim between the aft chainplate and bulkhead.
7. I had a polished backing plate fabricated for the cabin side of the thru-bolting.
8. Before reinstalling the chain plates, I cut away the deck and epoxy sealed the top of the port side, yet undamaged knee.

Except for recoring the knee, we effected the same modification to the port undamaged knee.

I have left the interior cover off the stbd side knee so that I could monitor any signs of failure to the newly cored knee. After 5 years, so far so good.

I am not an engineer, or a Boatwright, but I have to believe that an intact core in the knees creates needed dimensional rigidity and strength to the structure, similar to the coring in a deck. Take away this rigidity, and the layed up glass starts to work, and ultimately fail.

Regards
Rick Hurt
S/V Perla, P-40 #14

[Ben Nicol]

Thank you everyone for your input thus far. We really appreciate it.

@ Billy - I was thinking the same thing. They look quite well reinforced and there is signs of over glassing on some of the plywood that supports the white wooden liner. Also there is a triangle of wood cut from the bulkhead in the saloon and then covered with a removable teak trim. (not sure if original) I am still a little concerned about what would happen if the rot spreads. If the ply was just there to form up the shape, i guess the penetrating epoxy and the insert of a spacer like you install under a bushing ( http://autofab.com/images/F53535747.jpg ) may do the trick.

@ Rob - I would be my left one that that is where the water has come from and totally agree with you. We still have the teak decks in place and i was considering putting some raised blocks around the chain plates and other bits of hardware at a later date, about the same time we re caulk the teak. Thanks for sharing the designs.

@ Ernie - I have heard of the wonders of Butyl tape, yet to use it on anything of importance yet. Were your plates of the same design as Rob's ?

@ Rick - This is exactly what my worst case scenario plans look like in my head. Thanks for providing it in detail. I am working full time and am dreading paying for the operation. How long did it take you to complete ? Just to confirm - IMG_127 is the before photo of this procedure. This is pretty much what knees looked like, perhaps a little thinner.

Thanks,
Ben

[Jim Henerberry]

Hey Ben,

I went through the same project last summer and have posted a detailed explanation with a collection of pictures here:

https://groups.google.com/forum/#!searchin/PassportOwners/chainplate%7Csort:relevance/passportowners/kNQOw1i9ZqU/irkIx2G2BQAJ

To more directly address your question about the rot, I also drilled holes and poked into them with an ice pic, which felt bottomed out into solid wood fairly quickly.  When the knees finally started to come off the hull and I decided to remove them, I found mainly mush inside.  I am very glad I just took them off and rebuilt the whole thing.  My approach was to layer up plywood and sandwich straight stainless steel chainplates (standard issue from Schaefer Marine).  I then throughbolted the whole arrangement through the bulkhead.  I still need to replace my cap shrouds because the old wire has become stretchy.  I found it necessary to add a panting rod (mine is made of 1 x 19 wire with a turnbuckle, also known as a deck tie down, located on the forward side of the mast--I have a keel stepped mast) because the shroud tension now transmits directly into the bulkhead and appears to have squeezed things making everything, including some parts of the sole and the bulkhead itself rise up about a half inch.

If you do choose to keep your knees, I've heard here that other owners have tied them into the bulkhead using wood blocks and through bolts.  Before I did mine, I was considering an arrangement of angle irons (made from stainless, of course) to tie it all together.  I am happy with my choice, now that it's done.  I did work on it for about six weeks last summer maybe 4 or 5 days a week for maybe 3-6 hours per session.  That includes all the finish work as I had a bunch of rotted ceiling strips in the pullman too (those teak strips along the hull) and had to rework all that as part of the whole project.

Let us know what you decide to do.

Jim Henerberry

P40 Lottie B

1987, #123

[Ben Nicol]

Thanks Jim, 

Much appreciated. I think we will need to go down the rebuild path. I can see the same thing happening eventually. After much reading and thinking and things through i think we will need to bite the bullet. Attached is my reasoning for rebuilding the knees. Even if the rot is minor, it is probably worse than we think.

As the mast bends, the Cap and Intermediate shrouds will have un-equal forces, as they don’t attach to the same part of the mast. 

If the core is not present or not laminated correctly the fiberglass could begin to lift higher on one side than the other (shearing). Although only small movements, it could potentially create stress fractures, eventually breaking the knee away from the deck and the hull over time. 

Although drilling holes and filling with penetrating epoxy sounds like the easy fix, it wont ensure a lamination between both sides due to the fact that it will be impossible to correctly clean and prepare the bonding surface. We would just be filling center of the knee with epoxy, making it heavier but not necessarily stronger. 

Are there any obvious shortcomings to my reasoning ?

I think we will keep the knee and follow a similar process to RickH for now but before we do anything I want to do some more thinking. 

Ben