repair/replace chainplate knees

[richfriend]

I have Kells 28 Outrider (1976) which I acquired this spring and sailed (with some trepidation) this summer. Unfortunately, this boat has been neglected for some time and although the hull is watertight and without blisters, it has leaked severely at most every possible location on the cabin and deck fittings. I am in the process of removing and replacing the interior. None of the interior bulkheads appear to be supporting other than to keep the cabin roof from oil-canning. The chainplates are flat stainless entering thru the deck and bolted to the aft side of knees that are glassed to the hull. The knees at one time contained plywood which has transformed to garden humus. I have sliced off the interior edge of the knees and cleaned out the area where the plywood used to reside and had planned on replacing it with new plywood saturated with epoxy and then glass over the existing structure. My question (yes there is a question here someplace) is should I just hack the knees off entirely and make new ones from epoxy/plywood/cloth? The existing stucture appears to be about 5 or so layers of mat and cloth and is solidly bonded to the hull.

I guess I am lucky that Kells decided to mount most everything on the deck in areas where it is not cored so I only have one 1'x 2'area of the deck where the top skin has delaminated. The core is dry.

Any suggestions are appreciated.

Any thoughts on using dry douglas fir pressure treated lumber for interior framing? The wood has been stored inside (unheated) for 5 to 6 years.

RFriend

[bcooke]

My understanding is that the wood inside the knees is just there to give the glass some shape. The glass carries the load so the condition of the wood really isn't too important.

Now that you have cut into the glass however I believe the strength has been compromised. Rather than the fill and glass over method you mentioned I think I would go will new knees. It is relatively easy and you would be assured of a secure installation.

As for pressure treated wood, it is pretty heavy stuff but it will work.

-Britton

[Ancient Race]

Timing is everything, eh?

I'm just embarking on the same project on my Tartan-27. It's one of the standard restoration pains on Tartans, due to the builder's lack of foresight in encapsulating stainless plates in fg, where water intrusion in combination with the lack of oxygen causes them to rust out. The rest, as they say, is an ugly shortening of the rig. Sometimes rapidly.

Even more irritating is that D&M conveniently located the knees in the head and hanging locker, respectively. Here's the port knee and chainplate structure:


With the cabinet door open:


And the starboard:




You can note the exploratory holes at the bottom of the knees to determine whether they were wet, and the condition of the wood. Not good on either count, and so the replacement is in progress.

I've removed the doors on both the hanging locker and head, and pulled the head itself (sometimes POs are to be thanked for their decisions to pull head systems, replace them with dinky porta-pottis on scabbed-in chip-board bases). I've also removed all of the shelves, towel bars and other obstructions. I'll leave the bulkheads in place.

I don't have pictures of the work site with everything cleared out, but I'll provide a few, as well as photos of this weekend's demo process. At this point, the weapon of choice looks like a 4 1/2" Makita grinder with diamond blade - purpose-purchased for this job, due to the small size of its body. Reserves include a reciprocating saw, two circular saws, two drills and a hammer and chisel assortment.

My plan is to remove the knees, re-fabricate them of white oak, have the chainplates fabricated in new stainless, and re-tab and cover the whole assembly once again in fiberglass. I figure it lasted forty years the first time, the next owner can pay his own dues in another forty.

This is an ongoing problem on both East and West Coast Tartan's, and you might get some further helpful information on the T-27 discussion forum.

Greg

[Tim]

My understanding is that the wood inside the knees is just there to give the glass some shape.

This is only true in some cases, and normally when one is talking about internal stiffeners and stringers, where the molded shape of the fiberglass over the original wood creates a box structure that stiffens the part, with or without the original core material--be it wood or foam. Don't ever assume that wood inside an encapsulated structure is non-critical, though.

With something like a chainplate knee, the wood is important to resist the compression caused by tightening the bolts on the chainplate, as well as for additional shear strength. You could easily build a solid fiberglass structure that would work fine for the chainplate, but it wouldn't be smart to go on the assumption that the wood isn't there for a reason.

My question (yes there is a question here someplace) is should I just hack the knees off entirely and make new ones from epoxy/plywood/cloth? The existing stucture appears to be about 5 or so layers of mat and cloth and is solidly bonded to the hull.

Sometimes, starting fresh is easier in the long run, but there's also an argument for sticking with good, solid old material and replacing only what is necessary.

In your case, it sounds like you have two parallel pieces of fiberglass remaining, in between which once resided the plywood. Correct? If the area between is truly clean and readily accepts new plywood, it might be acceptable to insert a new piece slathered in thickened epoxy filler. You'd have to be sure that you had epoxy all the way around once the piece was inside the existing fiberglass, and then clamp it securely.

If you can't guarantee this, then you're better off replacing everything. But it sounds like you might successfully get away with the "easy" way out here, unless I'm misunderstanding the situation.

Any thoughts on using dry douglas fir pressure treated lumber for interior framing?

It will work just fine. Work boats often use PT for cockpit framework and the like, and it holds up fine. PT tends to be of poor quality, though, but if the wood's dry, as you say, it should have done most of its twisting, cracking, and so forth. Sometimes, though, ripping dimensional lumber like this (which I assume you would do, since using 2Xs for interior framework would be ridiculously heavy and bulky) can release internal tensions in the wood that make it spring and twist after the fact.

All in all, PT is OK for its intended usage for exterior building framing, etc, but I don't think it's great for too many other things. But that aside, there's no reason not to use it if you have a good supply that seems to be of acceptable quality.

[richfriend]

Thanks for the replies.

The sides of the knees are solid and well bonded to the hull. I sliced the minimum amount off to open them up and have cleaned one out to bare glass with a homemade sanding stick, 36 grit, in a sawzall. Not the most elegant tool but quite effective.

The pressure treated was hand picked to begin with -- nice straight grain -- and is very dry. I have ripped some other pieces into 1x2's and 1x1's without problem.

Now all I have to do is design the interior and re-build it.

Rfriend

I want to die peacefully in my sleep, like my grandfather,
rather than screaming in terror like his passengers.

[Rachel]

My plan is to remove the knees, re-fabricate them of white oak, have the chainplates fabricated in new stainless, and re-tab and cover the whole assembly once again in fiberglass. I figure it lasted forty years the first time, the next owner can pay his own dues in another forty.Greg

Greg,

Do I read this correctly that you plan to put the stainless chainplate tangs back inside the knees? That is, between the wood and the glass? Granted they did last this long that way, but I think I would favor remounting them on the outside of the glass... unless there's something I'm not understanding about your particlular situation (very possible).

--- Rachel

[Tim]

My plan is to remove the knees, re-fabricate them of white oak, have the chainplates fabricated in new stainless, and re-tab and cover the whole assembly once again in fiberglass. I figure it lasted forty years the first time, the next owner can pay his own dues in another forty.Greg

Greg,

Do I read this correctly that you plan to put the stainless chainplate tangs back inside the knees? That is, between the wood and the glass? Granted they did last this long that way, but I think I would favor remounting them on the outside of the glass... unless there's something I'm not understanding about your particlular situation (very possible).

--- Rachel

I agree. You'd be far better off simply securely glassing the knees in place and bolting the chainplates externally to the new knees. Glass over the top as original is a bad idea. Chainplates of this sort should always be available for inspection, in my opinion.

[Ancient Race]

Thanks Rachel & Tim -

I've actually been waivering awhile regarding the enclosed/accessible question. The debate is, of course: it ain't optimal, but it lasted forty years. I thought I'd make the final decision when the demo was done and I had a little more insight. Your views certainly incline me toward the accessible position, even if it means a slight realignment of the knee to achieve the same strength.

I'll start another thread on my own project this weekend, as I don't want to wander too far from RFriend's question. But if he's going to fabricate and install a new knee himself, let me ask about the hard spot issue here, as it might be relevant to his project as well.

The T-27 chain plate replacements generally go with the builder's encapsulation, and to my knowledge all but one have retained the wood - either marine ply or white oak. An issue with the wood/hull joint has been the need for a gasket between the two materials in order to avoid a hard spot.

I'm disinclined to believe it's necessary, if the fillet and tabbing are sufficiently solid that the knee isn't pushing against the hull.

Any thoughts?

Greg

[Quetzalsailor]

Re: pressure treated lumber. I replaced the engine beds in our old Morgan 27 with PT 2 x stock. Dimensionally the same as the mush that I removed. Tabbed with epoxy-glass. I do wonder about chemical compatibility but the local watermen do it with polyester and my epoxy showed no distress in the four or five years before I sold the boat.

Re: encapsulated plywood. Don't believe the Gougeon Bros when they write about wood saturated with epoxy; it really doesn't seep in all that far across the grain. What it does do is make the wood impervious to water; epoxy is far less permeable than paints and polyesters.

Re: replacing plywood once encased within 'glass. You have to decide whether the plywood is doing something or whether the plywood is a form for the original glasswork. When in doubt put it back just like the original designer intended. It'll be fine encapsulated in epoxy, including at the bolt holes. A quicky rule of thumb might be to observe whether the tabbing is really thick (1/4" or so) and complete or extending only about 4" onto the plywood. Complete encapsulation in epoxy is key. Sealing edges and holes in wood which extends out into the boat is key.

Re: replacing plywood with solid glass. Sure, make up panels in polyester-'glass - I cast on plastic on old window glass and cut the shapes I need; epoxy onto the place needing reinforcement. Remember that epoxy sticks to polyester but polyester does not stick to epoxy.

Re: cleaning out old wood from within tabbing and inserting new. Easy to say, probably really hard to do well; the surfaces need to be clean and dry. Make the insert marginally thinner/smaller, precoat all wood and glass surfaces with neat epoxy, liberally coat in thickened epoxy. I did the sawzall sander trick, too, to sand the interior of a centerboard trunk. It needs perfecting!

Re: encapsulating chainplates. If it's easy to do it right (not encapsulate)... Crevice corrosion would be unwelcome. That said, there's a lot of encapsulated carbon- and stainless steel (however there's ever less encapsulated carbon steel). Having replaced the encapsulated carbon steel backup plate under the Morgan forestay fitting after only 30 years...I can only wonder about the encapsulated stainless webs on our NE 38 after 36 years.