Simple wood questions

Discussion in 'Boat Design' started by banditv1, Sep 2, 2015.

  1. banditv1
    Joined: Sep 2015
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    Location: South Carolina

    banditv1 New Member

    Hello all,
    I new to the forums. So I apologize if I ask any previously answered questions. My questions have to do with plywood water proofing. To start with I don't know a whole lot about the process. So to provide you some context here is why I am asking. Marine plywood is hard to get and if you can find it the quality is very poor ( locally any way ). Therefore I am looking for an alternative. Something like a nice birch for example. While reading on this forum I have seen all kinds of answers to water proofing, IE epoxy this fiberglass that, gel-coats, and too many paint answers.

    Here is my current DIY why project so you can formulate any advice appropriately. I am going to build a one man miniature "Kentucky" flat bottom boat .. IE wood john boat. I can carry / roll to non boat ramp accessible locations.

    So if I am forced use an alternative wood, what is the easiest way to identify a plywood grade suitable to use in place of marine, and what method(s) could I use to water proof it. I would like to stay away from fiber glass if at all possible.

    As for advice, unless you can be clear, concise, intellectually accurate with the information please let some one else answer.

    Thank you all in advance !!
  2. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    If you don't want to use marine grade plywood (there is no such thing as poor quality marine ply, I think the worst allowable is BB grade) use regular old wood boards, such as 1 x 6s. Cedar is nice and light. Yellow pine is a lot more available, but heavyish. Jonboats were made from wood boards anyway. A ten footer might weigh 120 pounds if setup for a 15 hp outboard.

    However marine ply is not hard to find. You can order marine ply from any of 20 different suppliers and have it shipped (preferably to a friend with a business address to save the residential shipping address premium of about $50.)
  3. banditv1
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    banditv1 New Member

    Poor quality means excessive physical defects in the wood.
    I have very limited retailers in the area, and most retailers don't want ship two sheets without over charging you.
    Just clarify the question is "if I am forced to use and alternative" not about marine plywood qualities.

    Thank you for your feedback.
  4. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    For a small boat like you stated you can use ACX OR ABX plywood One A grade side one
    B or C grade side X means exterior grade using waterproof glue. Less than 1/2 the price of Marine. When using this coat both sides with epoxy 2 to 3 coats and edges. And your good to go.........................Make sure it is water PROOF GLUE
  5. philSweet
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Okay, but you can't easily waterproof a plywood jonboat. There is going to be exposed end cuts on the chines and the bow and stern transoms. And those are precisely the areas that get banged up. The interior will have gas and oil from an outboard, which even in small quantities is going to ruin most coatings in short order. Any coating system that even comes close will cost far more than just buying better material that can withstand getting wet.

    The cheapest epoxy I know costs about $35 for 1 gallon. That's about the same as a decent acrylic paint. But you will need more than a gallon, and you will need to seriously protect the chines and exposed edges. So a couple layers of fiberglass tape and a 1 x 2 rub strake glued over it. By now, you've added about 25 pounds to the weight of a 100 pound boat. And doubled the construction time. So maybe $100 in waterproofing materials to provide doubtful protection to stuff that falls apart when it gets wet, compared to just hammering a boat together out of wood boards or marine ply and painting the darn thing. The fact that it is a car topper suggests it wont be left in the water for weeks at a time, but where will it be stored? If outside, it will need to be under a roof of some sort and stored up on a couple saw horses.
  6. banditv1
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    banditv1 New Member

    That makes a lot of sense and clears up several points. That said here's an example of some of the materials that we used last time, we used marine plywood one sheet and two poplar 1 x 10's for the sides, bow and stern. Boat is meant to be light weight used with paddles or equipped with a trolling motor at most. Boat is stored outside and may or may not be covered at all times. We put on an oil based paint primer and used a good exterior paint. Boat lasted about seven years with minimal maintenance. I agree that marine plywood would be the best but in my local area it is hard to find high quality with out physical defects.

    Without knowing a lot about epoxies and other materials mentioned on the forums i am trying to theory craft a alternative material build.

    You mentioned building with boards, are you talking about side by side construction , tongue & groove, or dovetail styled ? I am interested in more input on this topic.

    Thanks again for all this feedback and information!!
  7. Petros
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    Petros Senior Member

    you could build with all sawn lumber, you can select the better examples from the stack at a big box store, and than remill it yourself on a table saw. to avoid all the caulking, you can use the canvas canoe kind of construction: frame and planks spaced with large gaps, and cover with heavy fabric, tack or staple to the gunwale (use a trim piece or rub rail to hide the staples or tacks after sealing), than paint with 5 to 7 coats of quality oil based paint, or polyurethane floor finish. they used to use canvas, but now you can get tough nylon or polyester fabric for much less, it is stronger and more rot resistant, as well as lighter. 8 to 10 oz per sq yd is good enough.

    Or you can eliminate more of the planks and go full on skin-on-frame. No plywood necessary at all, no caulking, and very light and inexpensive to build.

    On either method it would require you to repaint the sealant on the outside once a season, and replace the fabric covering about every 4 to 6 years. But that only takes less than $100 and perhaps 4 hours to do. It is fast and inexpensive way to build a light hull, though there is somewhat more maintenance over its useful life.

    I have built perhaps 20 skin-on-frame hulls, kayaks, canoes, and small dingy sailors. Material costs are only about $100-200 (usually can used salvaged lumber that is remilled to the correct size on a table saw). Very light construction, fast to build, and low cost, reasonably strong (that has to do with the strength of the frame, which is up to you), very water tight and sea worthy. Native Alaskans used to use this kind of construction on both kayaks (biadarkas) and up to 34 ft cargo hulls (unimks) for use in the arctic waters over long distances.

    It is a great way to make a small boat. Search google images for "skin-on-frame boats".
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    In your area, assuming the coastal portion of SC, there are several places to get both APA and LLoyds graded plywood. This said, don't use CDX, unless you want a very short lived boat. This grade of material is literally the lowest possible, has the most defects, is typically not rated "Exterior" but "Exposure 1" (big difference) and has the least number of veneers, per unit of thickness.

    If you must use construction grade, use "Exterior" grades. Marine (AA) grades don't cost much more than a good exterior sheet and this would be true of MDO as well.

    A "board built" boat can be done, but it'll leak like crazy in short order, if an outboard of any size is installed. These boats are typically "file planked" bottoms with a couple of "1 bys" on the sides. They're generally a fair bit heavier (50% or more) than a taped seam, plywood build too, mostly because the taped seam build doesn't need frames or floors or knees or any of the other usual structural elements installed.

    There are lots of plans for a small "clamming skiff" type of build, both traditional (plank on frame) or taped seam plywood. A traditional build will take longer, as it has many more parts to cut out and fit, compared to more modern build methods.

    I have a clamming skiff design take suggests taped seams, but you could skip the epoxy altogether and just use a goo in a tube (construction adhesive and caulk), knowing it's not going to be as tight or long lived.

    In the end, if you want light and car topable, taped seam or a SOF is the way to go. SOF is about as light as you'll get, but they tend to be pretty delicate, so consider it use, storage and durability in your area.
  9. banditv1
    Joined: Sep 2015
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    banditv1 New Member

    Thank you everyone this is good information. Now I have a much better understanding on the differences in the woods and quality.

    And thanks to searching this forum I may have found a good supplier for marine grade plywood.

    As I mentioned earlier we used to use poplar for sides, transom, and bow; when building the 16' boats. Poplar is available in my area, but before I build my miniature version of the flat bottom using old methods I would like some more advice.

    So lets assume I get the marine ply and go with the poplar ( unless you have a better suggestion ) for the rest of the boat. What is the best way for me to seal and protect it.? When I was a chap we used to just use a primer and a good exterior paint.
    But it seems a lot has changed since then, so I would like to know what you all think.

    Thank you all for your time and all the information / advice!!

  10. SaltOntheBrain
    Joined: Feb 2007
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    SaltOntheBrain Senior Member

    Medium Density Overlay.
    It's signboard. Good DF plywood with a paper/phenolic face that is made for sun and water exposure. Just build it and paint it. No Fairing to mess with except seams.
    And it's tough.
    Search on the Wooden Boat Forum for more info.
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