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Plywood Planking

Posted: Mon Dec 02, 2013 8:25 pm
by Bob Gerdisch
I have a side plywood planking question. Bonanza calls for 1/4 in planking. AA Douglas-fir is hard to find . Okoume equivalent 3MM is thinner. I hear it is not as strong as fir. The boat will have a mahogany veneer of 1/16 or 1/8 thickness. I wonder if AB fir with a veneer will do. I found some AB that looks as good as the AA I used on my Hot Rod. I know fir is tough stuff Okoume is not as strong. I would like to know what everybody is using on their boats. Thanks for any help.

Re: Plywood Planking

Posted: Mon Dec 02, 2013 8:42 pm
by galamb
If you can get a hold of AB fir that is more than sufficient - the inside face would just be a slightly lower grade.

And if you are putting a veneer over it, I would put the B face out and bond your veneer to that. The epoxy would neatly fill any (deformities) in the face veneer and make it stronger than an "A" rated face and considerably more durable.

Another note, 6 mil Okoume or Meranti would be the 1/4" equivalent, not 3 mil (about 24 mil in an inch).

The (mahogany) plywood are actually technically stronger because they have more plies than D-Fir plywood of the same thickness.

1/4" fir will normally be 3 plies. Since the plies are perpendicular to each other about 66% of the strength is in one direction (the 8' length) and 33% is vertical to the length.

The (1/4" - 6 mil) mahoganies are generally 5 ply so they are oriented 60%/40% so not as weak on their vertical orientation (but that is splitting small hairs).

If the cost is right I would go with the Fir - it will more than do what you are after...

Re: Plywood Planking

Posted: Mon Dec 02, 2013 8:49 pm
by Mannanj
6mm is roughly the equivalent of 1/4in. If you doubled two sheets of 3mm Okume you'd have 1/4in. (Roughly) Might think of doing that. What do the more experienced builders think? :?:

Re: Plywood Planking

Posted: Mon Dec 02, 2013 8:57 pm
by Bill Edmundson
Generally, the real marine plys are much better quality, fewer voids. Okume is the best to work with. Meranti is stronger. But, get ready to pull lots of splinters out of your hands.

Bill

Re: Plywood Planking

Posted: Tue Dec 03, 2013 4:15 am
by cusoak
I used the Meranti 6 mil on my Zip build and yes to the splinters that are small and hard to get out. But with the 5 ply's you get a lot more strength than with the 3 ply doug fir plywood makes for a sounder boat.
The more ply's in plywood the stronger it is. When I built custom furniture for a living we used 3/4" veneered plywood for the box part and it was 11ply.
Jeff

Re: Plywood Planking

Posted: Tue Dec 03, 2013 5:29 pm
by Bob Gerdisch
Thanks for the input.

Bob G

Re: Plywood Planking

Posted: Tue Apr 29, 2014 7:28 pm
by Brian
A question about butt-joining plywood sheets.

Glen-L provides guidance, advising NOT to put fasteners into frames on the first layer. Got it. They also provide info on joining panels, including butt-joints using a backing block. The first aft panel on my Monte Carlo landed pretty close to a frame, so I cut it to land on the center of the frame. then I blocked out the frame to give a surface of almost 4". My plan was to nail the edge to these blocks, but after understanding why they don't want you to nail to a frame, I've decided not to do that. My question is this: Why not still leave the joint there, don't nail it (the battens will hold the sheet) and then stagger the next sheet a few inches and repeat? Then the third sheet staggered the other direction. Then horizontal Sapele boards to finish. Seems like a really strong joint to me. No "hard spot" and no seam visible from inside.

This is the only place on the hull where this would be necessary. Any reason not to proceed with this plan?

Re: Plywood Planking

Posted: Tue May 06, 2014 8:21 am
by Gayle Brantuk
On a cold molded boat, the planking is fastened to the frames and longitudinals. We don't recommend butt joining the plywood over a frame because there isn’t enough material to properly join it.

Re: Plywood Planking

Posted: Tue May 06, 2014 10:46 am
by Brian
I've blocked the joint frame out to over 3", so I think with nails (as opposed to staples) and an overlapping next layer, it will be stronger than making a joint somewhere else with a backing block. I guess I won't know until the boat is bouncing along on Lake Tahoe!

Re: Plywood Planking

Posted: Thu Dec 24, 2015 2:50 pm
by Brian
I'm about ready to fiberglass the bottom on my Monte Carlo, starting with the aft 8 feet, since that's almost flat and easy. I laminated whole sheets of ply in this area. I've encapsulated the ply with Smith's CPES and run a long board (4' X 4") with 80 grit on it to show up high spots, and there is a fair amount of imperfection. It's mainly slightly low spots where the screws pulled the last lam in tighter to the battens and frames. We're talking maybe 1/32" in the worst spots, but a few fairly large areas (like 10" X 15").

I'm wondering how to attack this to get a really nice, flat finish. One way would be successive layers of resin on top of the glass, with lots of messy long board sanding. Another might be a skim coat of slightly thickened epoxy resin and sanding before fiberglassing. And yet another might be to just go ahead and glass it, then use one of the "high build" primers and sand that with the long board before final painting. Any thoughts on this issue? I'll need to do the rest of the bottom as well. So this is the easy part!

Re: Plywood Planking

Posted: Thu Dec 24, 2015 3:23 pm
by Roberta
My recommendation is to do all the filling and sanding prior to glassing to get the best possible finish. If you have lumps and voids in the planking, you risk sanding through the glass cloth while trying to flatten out the surface with long boards. I also recommend glassing the entire side, from shear to chine on both sides using one piece per side. Then do the bottom the same way. I would also use 3" glass tape on the chines and keel prior to glassing.

Roberta

Re: Plywood Planking

Posted: Thu Dec 24, 2015 4:05 pm
by jamundsen
order some micro balloons from Glen L. Mix it with whatever epoxy you're using. Make it thick like peanut butter. The thicker the better. make sure you mix the epoxy before adding the micro balloons. Spread it out fairly smooth with a smoother. wait until it drys. It sands easy but has very little structural strength. So its perfect for what you are wanting to do. The aft 10 feet of your Monte Carlo you want flat and perfect. This stuff will do it. Way easier than any other method. I had to do the last 3 feet or so on mine. I think there is a picture of the way the micro balloons turned out on the blog under my Monte Carlo. They're not in order so you may have to look thru some junk to find it. And Roberta is correct. Glass one half of the hull all at once. It goes pretty well. If I had to do it again I would use 6 oz.

Re: Plywood Planking

Posted: Thu Dec 24, 2015 4:10 pm
by Brian
Boat building fanatics communicating on Christmas! Yikes!

I plan on just glassing the bottom up to the chine, then glassing up to the paint line. That will handle the protection factor. I have another reason for not fib regulating the sides. This boat is being built in Hawaii, where we have 12-15% humidity in soft woods (like Sapele). It is going directly to Lake Tahoe, which is 6,000' and zero humidity. Although I'm taking every conceivable precaution (CPES, extra fasteners, lots of epoxy in the lams), there still could be some cracks develop on the sides (the bottom is 80% ply). If I glass the sides and there is some movement in the Sapele, it will be a huge job to fix. If I just leave it with CPES and a polyU finish, I can sand and refinish easily. Anyway, fiberglass on the sides is not much protection against a dock or another boat.

I guess your recommendation would be to skim the bottom with a slightly thickened epoxy, screed it out a little, then sand flat with a long board. This is what was recommended by the local glass guys. But the work involved is ominous. Sanding high build paint filler is much easier. Can't do this with a power tool, so it's a workout for several days involving weight loss. I just wonder if I am making too big a deal out of these imperfections. And, as I said, as I move forward it will be more complicated (although there are fewer and fewer such areas). Thanks for your response, Roberta, and Merry Christmas!

Re: Plywood Planking

Posted: Thu Dec 24, 2015 4:14 pm
by Brian
Thanks John. I was afraid of that. I have a tub of brown microballons, so will do that. Do you "screed" it with a board before it sets up to get it as flat as possible? I'm having trouble imagining how to do a large area with "peanut butter", without creating a month of sanding. A 3' long file would be handy! I suppose I could attack it initially with my 4" belt sander on low speed with a lot of movement, then the long board. But it's not going to be pretty after it sets up.

Re: Plywood Planking

Posted: Thu Dec 24, 2015 4:18 pm
by jamundsen
Dont use slightly thickened epoxy. That will kill you trying to sand it. It needs to be heavily thickened with Micro Balloons. Anything else will result in massive hours of sanding. Micro Balloons sands extremely easy.I put it on one night and sanded it down the next night in about an hour.
Micro balloons are white. They are cheap. I wish I had taken pictures of it. I just used a large smoother that you get for Bondo. You will not need the belt sander. Its just not hard to sand at all. If you were close Id give you all the Micro balolons you can use. I thought I would need a lot of it so I ordered a large bag from Glen L and found a little goes a long way. Maybe Ill just box some up and send it to you.
PM me your address.