Question about marine plywood

After years of accumulating plans to build a duck boat from gator wooden boats, devlin for the black brant III and now the Arthur Armstrong broadbill. I've decided to take the leap. I've cleared away space and started ordering tools and supplies. I had a question that came up in my head... Instead of using marine grade plywood-the okume 1088, can I use the sheets of 4 x 8 "plastic" wood ? I was watching a carpenter work with it the other day and went over and I was asking him questions about it. It comes in 3/8, 1/2, and 3/4" thickness. It's waterproof and he said you can bend it a little. To me it seems like it would take away from the chances of it rotting like marine plywood would over time of getting wet. I realize it would add weight but I don't see that as a bad thing. Before I make the final plunge and start buying wood can you folks please tell me the advantage/disadvantage please.

Thanks

Sab

 

Can you give me an example of this "wood"

 

The best way i can describe it is its like a pvc pipe material. I asked if it was waterproof and he said yes...thats why he was using it to make the eaves of the house. It feels just like the pipe you would use if you were doing drainage in your house. Thats the best I can describe it. Hope it helps

 

If you properly build an epoxy encapsulated plywood boat it shouldn't get wet and thus it shouldn't rot. Just keep filling the end grain and edges with resin and always use glass cloth to cover exposed surfaces to prevent checking and subsequent water entry.

 

It may not rot, but the strength of it for a given weight likely doesn't stack up, buy some and test against ply of similar weight.

 

not likely this plastic sheet has any meaningful strenth. If you get it thick enough to match the strength of plywood it would be very heavy and likely too stiff to bend without risk of breaking it. Plastic breaks down and crumbles away in sun light, so it would have to be heavily coated with opaque UV blocking paint.

Wood is fairly stiff and strong, yet can be bent into curves without loosing strength, it has a very high strength to weight ratio, and stiffness to weight ratio, higher than fiberglass, similar to Aluminum alloy. And likely the wood costs less and weights less than the plastic sheets of the same strength.

 

Petros contributed enough information to cause you to abandon the plastic wood option. Westfield told you how to avoid wood rot. Your question is a perfectly legitimate one. The answer is................use BS1088 ply if you want lightest weight, sufficient strength, and good long term surface quality.

 

Messabout you are correct. So much of what I fear about starting and completing a build is unreasonable, I know. I also know the biggest fear in doing it is just the unknown and forums like this and people like you guys gives all of us "paranoid" builders faith. Thanks for all the great replies and tour patients

 

I'm currently working up costs on a Mellonseed build, which is very similar to a what you'll build and the PVC siding stock you're referring to, is way too heavy for use. This alone should be enough, but in addition, these materials (PVC planking) aren't structural and can't even support their own weight, if one end is clamped in vice, while the other hangs free. Besides, it costs a whole lot more than wood anyway.

 

if you want practice building a boat go get a few sheets of inexpensive AC 1/4" plywood and a few fairly clear 2x4s to cut down into stringers and just throw together a small 8 ft pram dingy with hardware store supplies (deck screws, polyurethane adhesive, exterior paint, etc) and throw it together on a weekend. You can get plans all over the internet for free.

You can go out and play with it and not fear harming it. During the build, you will also not have any fear you are wasting a lot of expensive boat building lumber, it is a simple build so it will go fast, yet it will run you through all of the necessary steps and process to build the boat you really want, and it will give you confidence to move on to the "good" boat build with better quality materials and now more skills and experience. You can always give it away for some kids to use on a local pond once you are done with it.

It will also teach you that it does not have to be "perfect" to be a usable and enjoyable boat. And it will help you over come your fear of starting.

Just start!

 

We have a wide variety of opinions and knowledge here, but most agree - just start.

Boats cost some to a lot of money, but it is worth doing.

 

This advice is so simple and so perfect yet he thought never even crossed my mind. It's what I call a blinding flash of the obvious. Thank you again !

 

You also probably couldn't glue or fiberglass tape that stuff.

 

Using expensive okoumé plywood for a duck boat, even when it looks like a war machine, is a waste of money. Okoumé needs full sealing with epoxy for surviving and such a boat will have scratches all the time exposing the easily rotted wood.. A medium term is using meranti marine plywood, with better price, heavier but also stronger. On such a small boat the difference of weight will be without consequence, but you'll have to make a serious maintenance for the eventual scratches exposing the bare wood.

If the boat aesthetics doesn't bother you as you want only the function, "marine" pressure treated plywood -achtung generally these plywoods need to be dried before use-, stainless steel screws, some pressure treated wood and a 5200 polyurethane goey will do the job. You can paint or not paint as you want, provided that all the exposed cuts of the plywood are sealed with polyurethane in 2 times. First polyurethane slightly dissolved with synthetic turpentine for filling well the exposed part, and after curing one full day a good creamy polyurethane goey to full seal. The 5200 (or Sikaflex 251 or 281 I do not remember) serves also as glue combined with the screws. The main con is the weight.

If the boat stays in the water all the summer for example, the pressure treated plywood will soak too much water and become impossible to clean.
In this case a old fashion treatment like saturation of the surface with linseed oil doped with japan dryer (or zinc naphtenate), followed after full drying by 2 or 3 coats of old style oil paint or a simple alkyd will give a rustic look. The plywood must be perfectly dried before.
That's the old fisherman method for the small boats, easy to repair after the miseries of the season. You won't win a beauty contest but that works.

 

Ilan. I was always told, and everything I've read has said to use only the okume 1088. Up where I duck hunt the weather is brutal and the last thing I would want is any sort of problems. Thanks for the info but I think I'm just going to spend the few dollars more and use the marine plywood. Besides one of the best things for me...because I have 3 kids in college, is I can build it at my pace and pay for it little by little when I get some extra cash. I dont have to lay out all the money at once. Thank you anyway for the advice. This place has become my new favorite place to read and research on the net