Replacing Rotten Wood in Cabin Top

[rebel heart]

Cross layed plywood (30+ years), painted over. I've got a patch that's about 24" in diameter rotted fairly bad. No sunlight shining through, but one hammer blow could probably bust right through the thing. The real rot is a 12" diameter center. It's on the cabin top, and it looks like the offending leak has been fixed before. It's just dry rotted out at this point.

I used CPS just to try it out, and was thinking that I might just build the area up with some West + 307 fairing filler, smooth it out, repaint, and be done with it. Maybe put in a piece of cloth to add some strength, epoxy that in, then add the thicker epoxy compound, sand, and paint.

I'm a little spooked about cutting the wood out and replacing a 24" hole; maybe it's just psychological but it's freaking me out either way.

Does the epoxy repair sound legit, or chicken $h|+ ?

If I get a piece of plywood, would I "marine treat it" somehow?

[Pblais]

I'm a little spooked about cutting the wood out and replacing a 24" hole; maybe it's just psychological but it's freaking me out either way.

I agree a 24 inch hole is more than just a hole. In the end the bond at the perimeter will tell the tale. No matter what you do with the hole the edges have to bear the full load. Bridging over and / or under to solid material is what you need. This might be a time when traditional decoration might hide the patch.

Consider adding a hatch? When you can't win you can survive. Nature knows where the doors need to be.

[rebel heart]

Originally Posted by Pblais

I agree a 24 inch hole is more than just a hole. In the end the bond at the perimeter will tell the tale. No matter what you do with the hole the edges have to bear the full load. Bridging over and / or under to solid material is what you need. This might be a time when traditional decoration might hide the patch.

Consider adding a hatch? When you can't win you can survive. Nature knows where the doors need to be.

Funny you should mention that because I have a 4" solar vent that needs to go somewhere, and that location is as good as any other I suppose.

My neighbor (on a trawler) just repaired a section that was at least 5' by 8'; it was the entire aft deck for the most part. A huge section. The guy is a pack mule and I'm always stunned by what he can get done.

It just weirds me out to imagine putting a 4" hole into an already weakened spot.

[Pblais]

My last boats a CSY 33 had a 4 inch vent that was moved. 4 inches is not 24 inches. The permite relative to the sdquare area is nat that large with 4 inches. Your foot isn't less than twice that.

[fred]

24" is too large an area to patch with no support.
Is it near any cabin top overhead girders? Perhaps some bridging or blocks could be put between the girders to support the patch.
A hatch gets my vote....
A great idea, Pblais....
I've had many boats and not one had 'enuf' ventilation.

Think of it like the floor of a house.
Would you walk on a patched floor, that did not have a floor joist under it?



fred

[Jesse]

Paul and Fred are on the right track. The rotted area must be removed at any rate,if not it will simply grow to engulf the entire cabin top. A hatch is one way to replace the material you take out and the added light and ventilation would be beneficial. Jesse

[clausont]

RebelHeart - you will probably find it easier that you had expected it to be once you get started. Wood is not that hard to work with. Here is a little project that I am doing on our Ingrid:
Head knocker From Deck on Flickr - Photo Sharing!
Not Anymore! on Flickr - Photo Sharing!
Head Knocker From Below on Flickr - Photo Sharing!

Don't look too closely at the quality of my work - its not pretty. But it's not finished yet either. Even at this point it is water tight - I know for sure because of the amount of rain that we have had in the last few weeks since I did this part!
You will do just fine with your repair. Sounds like a good time for a new hatch

[rebel heart]

Claus;

Thanks for the words of encouragement. Part of the difficulty I have is just the part where I need to take a saw and cut such a big hole in the boat, but I really want to do it the right way and not cheap out.

The area itself is beveled / curved, so a flat hatch probably won't do me much good. There are joists along the cabin top separated at 13" intervals or so.

How do you deal with a piece of wood that needs to be curved like that?

[s/v Jedi]

How do you deal with a piece of wood that needs to be curved like that?

Rebel: you don't. Cut the 12" hole and check the wood; keep cutting it bigger until you find good wood without rot. Now bevel it to 12:1 so that the outside diameter is the bigger one, using plane, router, beltsander etc). Now take 3-ply plywood, cut roughly to shape and have someone push it onto the hole from inside. mark it from the outside. Enlarge the markings to half the 12:1 bevel size and cut. It will now fit in there, with the edges halfway the thickness of the cabin-top. See if you can compound it a bit to have the same curves, practice a bit how and where to push. Now, wet the bevel and 3-ply edge out and mix a batch of thickened epoxy, using medium density filler to peanut butter consistency. When the wet-out starts gelling, apply epoxy generously, push the panel in and do the pushing/compounding for best shape while tacking the edges in place. Remove excess epoxy with rounded end of stick so that you leave a little fillet in place. Let cure.

Now, you build both outside and inside up using fiberglass cloth or woven roving if thickness allows (every layer on outside bigger cloth, inside smaller to fill up bevel) and find a fairing-wizard for final looks or try yourself with long thin batten. Sand, paint.

All but the fairing and painting part is easy. I succeeded with similar projects without ever having it done before. I did have some fiberglass experience like building model airplanes but nothing special.

cheers,
Nick.

[Wotname]

Originally Posted by rebel heart

If I get a piece of plywood, would I "marine treat it" somehow?

Yes, with epoxy.

Originally Posted by s/v Jedi

Rebel: you don't. Cut the 12" hole and check the wood; keep cutting it bigger until you find good wood without rot. Now bevel it to 12:1 so that the outside diameter is the bigger one, using plane, router, beltsander etc). Now take 3-ply plywood, cut roughly to shape and have someone push it onto the hole from inside. mark it from the outside. Enlarge the markings to half the 12:1 bevel size and cut. It will now fit in there, with the edges halfway the thickness of the cabin-top. See if you can compound it a bit to have the same curves, practice a bit how and where to push. Now, wet the bevel and 3-ply edge out and mix a batch of thickened epoxy, using medium density filler to peanut butter consistency. When the wet-out starts gelling, apply epoxy generously, push the panel in and do the pushing/compounding for best shape while tacking the edges in place. Remove excess epoxy with rounded end of stick so that you leave a little fillet in place. Let cure.

Now, you build both outside and inside up using fiberglass cloth or woven roving if thickness allows (every layer on outside bigger cloth, inside smaller to fill up bevel) and find a fairing-wizard for final looks or try yourself with long thin batten. Sand, paint.

All but the fairing and painting part is easy. I succeeded with similar projects without ever having it done before. I did have some fiberglass experience like building model airplanes but nothing special.

cheers,
Nick.

I tend to agree with SVJ here but what is the thickness of the ply you replacing?

If greater than say 3/8", I would laminate up the new piece in a similar way to SVJ but use say two or 3 pieces of 3/16" etc.

I would ONLY use marine plywood regardless of what others say about epoxy and commerical ply. The amount of labor is significant so why mess around with a second rate material.

[amarinesurveyor]

You've got to get rid of that rot but cutting it out. After cutting, make sure there is no rot in the supporting beams...there is a good possibility that that they are affected also. Don't ignore it; don't patch it with epoxy filler; replacing the wood is the only way to go in my opinion.
Brian

[rebel heart]

Originally Posted by s/v Jedi

Rebel: you don't. Cut the 12" hole and check the wood; keep cutting it bigger until you find good wood without rot. Now bevel it to 12:1 so that the outside diameter is the bigger one, using plane, router, beltsander etc). Now take 3-ply plywood, cut roughly to shape and have someone push it onto the hole from inside. mark it from the outside. Enlarge the markings to half the 12:1 bevel size and cut. It will now fit in there, with the edges halfway the thickness of the cabin-top. See if you can compound it a bit to have the same curves, practice a bit how and where to push. Now, wet the bevel and 3-ply edge out and mix a batch of thickened epoxy, using medium density filler to peanut butter consistency. When the wet-out starts gelling, apply epoxy generously, push the panel in and do the pushing/compounding for best shape while tacking the edges in place. Remove excess epoxy with rounded end of stick so that you leave a little fillet in place. Let cure.

Now, you build both outside and inside up using fiberglass cloth or woven roving if thickness allows (every layer on outside bigger cloth, inside smaller to fill up bevel) and find a fairing-wizard for final looks or try yourself with long thin batten. Sand, paint.

All but the fairing and painting part is easy. I succeeded with similar projects without ever having it done before. I did have some fiberglass experience like building model airplanes but nothing special.

cheers,
Nick.

Nick;

That's awesome man. Thanks for the step by step on this stuff. There was nothing in me that felt good about leaving that crap wood in there. So it looks like this weekend is going to be project time.

A couple other questions if I can:

a) I would think cutting out a rectangle would be a lot easier than cutting some weird polygon, right?

b) I'm familiar with the concept of scarfing, but I've never done it before. I found this good link, and will look around the Internet for some others: Scarf Bevel Cutting . I'll probably try to do a sample scarf in a spare board before I do it on the real repair. Overkill?

c) When you say "tack the edges in place", do you mean to use finishing nails or something of that sort, in order to hold the woods together to let the epoxy cure?

And please feel free to add more info; t-minus 4 days till I start on this thing.

[rebel heart]

Just for anyone else who finds this thread, I found a good article on scarf bevel cutting, and a reference to how to use a power planer properly:

Scarf Bevel Cutting

http://www.boatdesign.net/forums/woo...o-23215-2.html

How to Use a Power Planer | Tools | Reader's Digest

I'm sure this seems really elementary to you handy wood workers (or just handy people in general), but to me it's like building an atom bomb.

[rebel heart]

Sorry I'm just having some "duh!" moments right now as I'm working this out in my head. So it really just comes down to:

a) Cut the hole.
b) Take the width of the wood (1/2"), and multiply by 12 (6").
c) Draw a line 6" from the edge of the hole with a marker.
d) Using a hand or power plane, make an angle from the marker to the hole.

So conceptually that doesn't seem very hard at all. Step (d) looks like it would be hard to get right.

[DeepFrz]

Before you do anything, use a hole saw (in a drill) and cut out a small piece (1") to see what your layup is. If you have fiberglass on the top and bottom with a plywood core then there is no need to cut the hole right through. Keep the bottom layer and you wont be working overhead with epoxy, which is a messy, horrible job. Just tape over the hole in the bottom with packing tape before you start the epoxy job.

There is a good article on the West System web site on deck repair which you can read to see what they did.

WEST SYSTEM | Projects - Boat Repair