plywood bottom rotting

[Cale]

I have a 26ft chris craft and the plywood on the bottom and sides is very weak and in some places rotted should I put new plywood over this, or should I cut out and patch all bad areas.

[The Bigfella]

Photos would help, but a re-skin may be your best option. Definitely NOT over the top

[Andrew Craig-Bennett]

What Ian said. NOT over the top. Plywood does have a finite life, alas. Once moisture can travel in from the end grain, its pretty much all over, as the glue stops the ply from ever drying out again.

[Cale]

If I was to replace the old plywood with new do I just but the ends and sides together and put some epoxy on all joints as well as the braces? What kind of epoxy should I use? Should I countersink my screws and glue bungs over screws then start the finish work? Any ideas or pointers would help this is my first wood boat and I thought that since I love to wood work that it would be a good project but the more I read about this stuff the more I think that I took on a project to big for me.

[MiddleAgesMan]

Where new meets old you should use a scarf joint, not butt. It's a little tough putting the scarf in the old ply that's still on the boat but it can be done and frequently is.

On the other hand, if you can live with a little imperfection you could use a Payson butt joint with a layer of glass inside and out across the joint. That joint is frequently used in new stitch and glue construction. It might work for your repair but it won't be as strong as scarfing.

[Cuyahoga Chuck]

You should poke around the internal framework now so as not to be surprised when the ply comes off. The usual tool is something like an old fashioned ice pick. Long,thin and sharpely pointed.
Poke around any framing that is close to the area of rot.
As long as the can or jug says "EPOXY" on it it should do the job. It may take two applications because end grain tends to wick away from the surface.

[pcford]

All bottom planking should be replaced. If you replace part you will likely be replacing the rest in a few years.

Rot spreads rapidly in plywood. Just another reason not to use the stuff when choosing a boat design to build.

It is very likely that the sides may have to be replaced as well.

With all of the said, it is not a huge, huge job. Plywood goes on fast.

[abbyj]

I have a 26ft chris craft and the plywood on the bottom and sides is very weak and in some places rotted should I put new plywood over this, or should I cut out and patch all bad areas.

First of all, don't get discouraged by the "solid wood" snobs here. No rainforests were raped in order to build the hull your 48 year old boat. Just Douglas Fir plywood made in North America. I also I don't think she has ever had to be re-caulked or re-fastened;).

One of the neat things about plywood is it's dimensional stability. Localized rot repairs are pretty easy, and entire sheets can be pulled, traced over a new sheet and installed.

Shoot some pics for us, and if needed, ask for info on how to post them.

There are a couple of other Boat-Building sites where you'll see less opinionated snobbery and more genuine advice. One is the

BoatDesign.Net forum (http://www.boatdesign.net/forums/), There is a good deal of Chris-Craft posts over there, and a respect for all boats, regardless of their construction.

Duckworks (http://www.duckworksmagazine.com/08/features.htm) also has some neat "How To" articles, and other links

Be sure to check out Glen-L's Forum (http://www.glen-l.com/phpBB2/index.php)also. Though some of the talk is specifically dealing with Glen-L boat designs, It's a great group of helpful folks, and a place where plywood is seen as "rotary peeled wood veneer, in multiple layers, oriented at 90 degrees to other"

Hope this all helps, look forward to pics

[botebum]

Years ago I had a side job patching in some planking on the same model(more or less) as yours. The yard had dropped the boat onto the jackstands and holed it. IIRC the original planking was butted with butt-block backers. When I repaired it I made sure I crossed at least 4 frames/ribs and staggered the joints by at least 2. The resulting patch of a 1'x1' hole ended up being almost 6' long. I bedded the new planking in dolfinite, I think. One frame/rib had to be replaced. The lady only wanted to fix the boat up for a couple more seasons. Before I knew that I was suggesting either a total rebuild or selling it to someone who wanted a project. The transom was on it's way out and the engine beds were getting kind of punky. The stem looked like they'd been pushing barges up the Hudson and the foredeck and cabin top were goners through neglect. Some of the bottom planking was soft and I did everything I could to convince her that it wasn't really a safe situation. The customer got what she wanted:rolleyes: I charged her around $900 in 1998.

Doug

[oakman]

It's not snobbery abbyj, it's reality. Plywood or oriented veneers, or whatever you want to call it is a sponge waiting to happen. Leave a piece of marine grade ply out in the weather along side a piece of white oak or any of the many species of wood with rot resistance usually used in boat construction and the solid wood will outlast the ply every time. Just the truth.

As to the rainforest, yes, some evil was done, but many people are now building responsibly using sustainable products. Why don't you check out the carbon footprint for the making of a single sheet of ply, also check out the poor sod in the factory making the glue for all that ply, bet he's not so happy.

Yup, give me solid wood every time and while you are epoxying and grinding and scarfing, I will pound in some beautiful white cotton and go sailing.

[pcford]

It's not snobbery abbyj, it's reality.

Our pal abbyj does seem to have a bit of a chip on his shoulder in this regard.

A few points: Plywood is a fine material from which to build a boat. It is possible to build a boat relatively quickly and easily from the material. Some folks start with plywood in their first attempts at building. And you can get a fine boat.

However, one has to be aware of the materials limitations. One of the problems with the material is that when it begins to rot, the rot can spread very quickly over a wide area.

A couple examples.

A guy came into the shop with a 20ft. plywood lapstrake Chris Sea Skiff with some soft wood on the bottom. By the time I was done, the boat had original planking above the water line, original transom and original "furniture" and windshield. Everything else was new wood: Entire bottom, frames, stem, bulkhead, stringers....you get the idea. Cost the owner a few tens of Ks.

Another time a client came in the shop with a little 10ft plywood boat with fins.

Parenthetical statement:

(Owner was a woman, by the way. One of the two women for whom I have worked in 35 years of doing this stuff. Note to you youngsters out there: if you want to meet women, doing boat restoration ain't the place to do it. Women usually come into the shop with their boyfriend or husbands. If they are with their boyfriend they are being indulgent about his boat. If they are with their husband, they just are pissed off. Not 100% of time but maybe 90%.

By the way, both women were excellent clients...way better than average.)
The owner had an attachment to her boat...so I rebuilt it..cost about $5K.

Both of these amounts were long ago...maybe 15 years or more...price would be significantly more now.

The point is that doing a rot job on a plywood boat has to be approached realistically. There is a very real possibility that it may entail doing more the just a patch here or there.

Regarding plywood in general. Most professional boatwrights prefer not to work with the stuff. It's just not pleasant to work with.

For amateurs...doing this stuff for pleasure...I would certainly recommend using solid timber for building.

[oakman]

Well PC that puts it rather plainly. Better than my snide reply, sorry for that. . .

What PC said. . .

[Cale]

I am just getting into this wood boat stuff. Someday I would like to have a hardwood sailboat but this one just fell into my hands. I got it for free so I thought it would be a good first project. I would like to find a way to find out what it would be worth if complete brand new looking. Thanks for all the info, I will try to post some pics when I get the chance to take some.

[botebum]

Complete and brand new looking? As in take it to shows and such? It'll be worth a pretty good chunk of change but you'll still have more in it than it'll be worth. Do it for the love, not the money.

Doug

[Excalibur]

However, one has to be aware of the materials limitations. One of the problems with the material is that when it begins to rot, the rot can spread very quickly over a wide area.

A couple examples.

A guy came into the shop with a 20ft. plywood lapstrake Chris Sea Skiff with some soft wood on the bottom. By the time I was done, the boat had original planking above the water line, original transom and original "furniture" and windshield. Everything else was new wood: Entire bottom, frames, stem, bulkhead, stringers....you get the idea. Cost the owner a few tens of Ks.



PC, I can readily understand how one large sheet of plywood can wick water and rot everywhere quickly. But how can water and rot get quickly across the lapstrake? Isn't it still individual pieces separated (in the case of the Chris Craft) by thokiol?

Cale, is your boat lapstrake or large sheets?

[pcford]

PC, I can readily understand how one large sheet of plywood can wick water and rot everywhere quickly. But how can water and rot get quickly across the lapstrake? Isn't it still individual pieces separated (in the case of the Chris Craft) by thokiol?

Cale, is your boat lapstrake or large sheets?

First, the bottom on these things is essentially one big sheet. However, I am sure there were at least a couple more strakes involved at the turn of the bilge. These adjacent planks rotted like the nearby engine stringers and stem.

I believe Cale said his boat was a Cavalier model. That means sheet plywood, not lapstrake. Sea Skiff model line are lapstrake.

[Cuyahoga Chuck]

I am just getting into this wood boat stuff. Someday I would like to have a hardwood sailboat but this one just fell into my hands. I got it for free so I thought it would be a good first project. I would like to find a way to find out what it would be worth if complete brand new looking. Thanks for all the info, I will try to post some pics when I get the chance to take some.

Chris Craft mahogany runabouts can be worth big bucks.
If you can find ACBS (Antique and Classic Boat Society) chapter near you they may be able to offer guidance.

[pcford]

Chris Craft mahogany runabouts can be worth big bucks.
If you can find ACBS (Antique and Classic Boat Society) chapter near you they may be able to offer guidance.

Cavaliers...not so much.

[Excalibur]

PC, I just went over the thread again. Cale hasn't told us what he has yet. Maybe the small Sea Skiffs have a big sheet, but my 38' is all ply (lapstrake) planking under water. The topsides are carvel and not ply.

[pcford]

PC, I just went over the thread again. Cale hasn't told us what he has yet. Maybe the small Sea Skiffs have a big sheet, but my 38' is all ply (lapstrake) planking under water. The topsides are carvel and not ply.

Hmm, never noticed that some Sea Skiff were only lapstrake part way up. Oh, your boat is seam-batten not carvel on topsides.

[Thad Van Gilder]

[QUOTE=abbyj;1952950]First
of all, don't get discouraged by the "solid wood" snobs here. No rainforests were raped in order to build the hull your 48 year old boat. Just Douglas Fir plywood made in North America. I also I don't think she has ever had to be re-caulked or re-fastened;).

That's funny, I thought doug fir came from a temperate rain forest...

ah, what do I know.

-Thad

[Thad Van Gilder]

ah the cavalier dory. neat center console design. I put a bunch of strakes on one years ago.

-Thad

[brad9798]

Back to the original question, I have a 35' Cavalier aft-cabin ... plywood, of course.

You guys remember, the throw-away line from CC back in the day.

Plywood is relatively easy to replace, even for the modest woodworker.

You will want to make your joints on frames.

BUT make sure the frames are solid, if not you will have to cut the bad part out and sister/replace them.

Butt joints have NEVER given me problems on MY LADY! Not one.

Scarfs are better ... but for my 44 year-old boat, butts are fine, and even I can't tell where they are without sometimes measuring!

[Cale]

Thanks Brad you really put that in good prespective also I feel that the but joints will be fine, what is the best way ro seal the new plywood before I put it on.

[brad9798]

CPES is good ... a GOOD MARINE-GRADE ply will make all the difference!

My boat is the envy of the harbour ... even with butt joints! ;)

Folks can say all they want about plywood ... but, unlike the Constellations, my boat is still over 60% ORIGINAL plywood!

B

[brad9798]

Some epoxy is good, too! West System is what I have used for the past 10 years!

[pcford]

You will want to make your joints on frames.



Butting the plywood on frames is certainly not appropriate.

[brad9798]

I am no shipwright ... but like I said, I have been the envy of the harbour for years.

My boat looks top-notch ... even if she is not perfectly repaired!

I have trophies to prove it! ;)

pcford- I know you KNOW your stuff, but I am a laymen!

Brad

[Cale]

Butting the plywood on frames is certainly not appropriate.
Then how should I do it ?

[Excalibur]

Hmm, never noticed that some Sea Skiff were only lapstrake part way up. Oh, your boat is seam-batten not carvel on topsides.

Yup, happened late in the wood boat series (mid late 60's). They added the "Corinthian" moniker at that point for smooth sided topside models, so I officially have a "Sea Skiff Corinthian".

I got the "carvel" label from Chapelle, who said that " Carvel, or smooth-skin planking is the orthodox method;" and "In some designs having carvel planking the seams are backed up with battens; this is known as "ribband carvel" or seam batten construction"...

You are right that calling it "carvel" is imprecise. It is seam-batten.

[pcford]

Yup, happened late in the wood boat series (mid late 60's). They added the "Corinthian" moniker at that point for smooth sided topside models, so I officially have a "Sea Skiff Corinthian".

I got the "carvel" label from Chapelle, who said that " Carvel, or smooth-skin planking is the orthodox method;" and "In some designs having carvel planking the seams are backed up with battens; this is known as "ribband carvel" or seam batten construction"...

You are right that calling it "carvel" is imprecise. It is seam-batten.

I always think of carvel as having traditionally caulked seams.

Don't know if that is the "official" definition.

[Excalibur]

I always think of carvel as having traditionally caulked seams.

Don't know if that is the "official" definition.

I got most of my learning from books and not by doing, so I'll take yours as "official". Mine's mostly second hand.

[neilm]

I know boatbuilders don't use treated plywood much because of it's low grade but after my inflatable bottom of mahogany marine plywood fell apart I decided the next floor would be treated plywood. I didn't paint or epoxy anything, just cut it to shape and layed it down. After eight years of mostly wet environment I inspected it and it has show no sign of rot or delamination. I'm sold on treated plywood. I just wish I could get it in Marine grade or ACX.

Neil

[pcford]

I got most of my learning from books and not by doing, so I'll take yours as "official". Mine's mostly second hand.

I'll take that as a compliment. However, one thing that I have always preached in these venues is not to take the word of any one guy...even though he may think his opinion is gospel.

Lots of self-appointed experts around here. Who knows, maybe I should get a wood as engineering material book so I can be an expert too.

[abbyj]

[quote=abbyj;1952950]First
of all, don't get discouraged by the "solid wood" snobs here. No rainforests were raped in order to build the hull your 48 year old boat. Just Douglas Fir plywood made in North America. I also I don't think she has ever had to be re-caulked or re-fastened;).

That's funny, I thought doug fir came from a temperate rain forest...

ah, what do I know.

-Thad

For every tree cut, 2 or more are planted. Outside of North America, One tree cut, A patch of alternative fuel (soy, cane) grown.

[abbyj]

I know boatbuilders don't use treated plywood much because of it's low grade but after my inflatable bottom of mahogany marine plywood fell apart I decided the next floor would be treated plywood. I didn't paint or epoxy anything, just cut it to shape and layed it down. After eight years of mostly wet environment I inspected it and it has show no sign of rot or delamination. I'm sold on treated plywood. I just wish I could get it in Marine grade or ACX.

Neil

Closest thing to date:

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