Marine plywood choice

Discussion in 'Boat Design' started by jazman1978, Apr 17, 2009.

  1. jazman1978
    Joined: Apr 2009
    Posts: 13
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: South Carolina

    jazman1978 Junior Member

    I am building a small flat bottom boat, about 12'" x 4', and was wondering if I really needed to use Okoume or Meranti plywood. I only plan on having it in the water 10-20 times a year. I have looked for AC Exterior Plywood, but have had no luck finding it. I can order Okoume and Meranti plywood online, but it is pretty pricey. Can anyone help me with this?
     
  2. PAR
    Joined: Nov 2003
    Posts: 19,126
    Likes: 498, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    A 80 pound Meranti boat will weight 64 pounds if Okoume. Okoume has less rot resistance then Meranti, but this point is relatively moot if you use epoxy encapsulation methods.
     
  3. marshmat
    Joined: Apr 2005
    Posts: 4,127
    Likes: 149, Points: 63, Legacy Rep: 2043
    Location: Ontario

    marshmat Senior Member

    Hi jazman,

    You probably don't need okoume or meranti, but you do need something with a truly waterproof glue and with continuous, gap-free core veneers. Usually, that means something marked as "Marine AA" or "Marine AB".

    Some designs, such as Phil Bolger's small plywood boats, are designed with scantlings that account for the defects and weaknesses in exterior-grade ply. (My own boat, a Bolger design, is built with AC exterior.) If the designer's specifications allow this, suitable exterior ply needs to have reasonably gap-free core layers of a good quality wood (some exterior ply uses short-lived, rot-prone junk in the core and a better species on the surface), as well as a truly waterproof glue.

    If the designer's specs call for marine-grade ply, then you're taking a substantial risk if you move to cheaper stuff. Especially on a boat this small, which likely has a fairly thin hull skin, you could be inviting structural failure if you use a lower grade of ply than the designer intended.
     
  4. jazman1978
    Joined: Apr 2009
    Posts: 13
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: South Carolina

    jazman1978 Junior Member

    Thanks for the tips and I agree that I need good quality plywood. The plans I have are from gatorboats.com (Big Mamma) and they call for AC exterior ply. This is such a simple dinghy type boat that I feel the AC is adequate. Does anyone know where to find a supplier for AC? Lowes has an AC Pine shown online, but it's not available in any stores that I could find. If you couldn't tell this will be my first attempt at this, so any good info anyone has will be greatly appreciated.

    Josh
     
  5. rasorinc
    Joined: Nov 2007
    Posts: 1,853
    Likes: 71, Points: 48, Legacy Rep: 896
    Location: OREGON

    rasorinc Senior Member

    When you look for exterior ply it is called CCX-PTS for plugged, touched and sanded. Mostly used for overhangs that is why it is PTS. same glue as in Marine grade ply. Should be avaiable in most all lumber yards but not Home depot however Loes may carry it. comes in 1/2, 3/8. 5/8, and 3/4. I know all the lumber yards in Tenn. carried it. CCX is EXTERIOR CDX is interior
     
  6. JULIA DREAM
    Joined: Apr 2009
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: milky way

    JULIA DREAM New Member

    "CCX is EXTERIOR CDX is interior" I believe that CDX andCCx are both exterior. Look at American plywood manufactorers websight. the first two letters designate quality of side A best then B and so on. X is for....EXTERIOR :) Same glue used for exterior as marine. Voids are spected out on websight. I used BCX on one project and left it out in a fiedl unpainted for two years and it is still in amazingly good shape except for one sheet which delaminated a bit...five billion times cheaper than Marine stuff. Cheers!
     
  7. rasorinc
    Joined: Nov 2007
    Posts: 1,853
    Likes: 71, Points: 48, Legacy Rep: 896
    Location: OREGON

    rasorinc Senior Member

    CDX is interior. You were lucky. We use CCX on overhangs and CDX on the interior of the roof field. If the CDX has the same adhesive and it is posted same then the mill that made it is doing you a favor. Do not think it is the same adhesive though. Why try and hope when CCX is a national standard.
    Different mills my not be the same.
     
  8. marshmat
    Joined: Apr 2005
    Posts: 4,127
    Likes: 149, Points: 63, Legacy Rep: 2043
    Location: Ontario

    marshmat Senior Member

    APA requirements for exterior grade ply do not permit D-grade veneers.

    It is my understanding that "CDX" is usually APA rated sheathing exposure 1. That is, it's rated to withstand temporary exposure before being protected (ie, as house sheathing under the air barrier membrane) but cannot be used in exterior applications where it would be permanently exposed to weather.
     
  9. PAR
    Joined: Nov 2003
    Posts: 19,126
    Likes: 498, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Lets get the terms right folks. If it has a X on the end, it's rated exterior and has waterproof glue.

    BCX and ABX or ACX are suitable for bulkheads, furniture and other items in a build, but I wouldn't use it for planking on all but the cheapest and shortest life expectancy project.

    Construction grades just don't bend uniformly, usually popping, kinking or developing some sort of deformity in the process. The smaller the boat, the "quicker" the curves, which makes this issue a bigger contention for the builder.

    The problem with the plywood grading system in the USA is it's a "voluntary standard" set by the APA. Each mill will set it's own standards and put what ever label on it they think they can sell it for. The only proof in the pudding is to physical examine each sheet for the common set of flaws.

    If the original poster (Jazman1976) drops me an email, I know of a few suppliers in his area, where he can pick up Okoume, meranti or fir construction grade plywood.
     
  10. jazman1978
    Joined: Apr 2009
    Posts: 13
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: South Carolina

    jazman1978 Junior Member

    I appreciate everyone's input and opinions. This is the first project I have ever done that I needed to be concerned about the grade of plywood. I am learning a lot. Thanks
     
  11. jazman1978
    Joined: Apr 2009
    Posts: 13
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: South Carolina

    jazman1978 Junior Member

    I though I would attach a picture of what my boat could look like. I will probably paint it with an oil base paint for the final finish though.
     

    Attached Files:

  12. ecflyer
    Joined: Jan 2009
    Posts: 81
    Likes: 4, Points: 0, Legacy Rep: 72
    Location: Green Bay, Wisconsin

    ecflyer Junior Member

    Jazman
    I"ll let you in on a trade secret. I'm an old carpenter with 50 years experience. You can use 1/4" 5 ply plywood that is rated for interior underlayment to be used under vinyl kit floors. It is made with exterior glue and has almost "0" voids in the inner plys. You can verify the exterior glue by looking at the gluelines at the edge of the sheet. If the glue line is dark brown/black then it is a resourcenal glue and is as water proof as you can get. The reason there are no voids in this ply is as follows: If a 150 # woman walks across a vinyl/kitchen floor with 1/4" spiked high heels, she exerts 600'#s per sqr. inch to the floor. If there were a void in an inner ply, she would punch a hole right into the flooring. This is totally unacceptable in home construction. If you can use more than one layer of 1/4" ply in building your hull (5 plys/piece) you will have a really strong boat. Now you know something about ply that even navel architects don't know.
    Good boat building
    Earl
     
  13. Wynand N
    Joined: Oct 2004
    Posts: 1,260
    Likes: 148, Points: 73, Legacy Rep: 1806
    Location: South Africa

    Wynand N Retired Steelboatbuilder

    stick to the right stuff - BS1088 grade marine ply...
     
  14. jazman1978
    Joined: Apr 2009
    Posts: 13
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: South Carolina

    jazman1978 Junior Member

    I just purchased some AC exterior lumber this weekend. It was much more cost effective than the higher grades, and it's what my plans called for. I will remember the underlayment idea if I build another. That would make it a good bit lighter.
     

  15. Steve W
    Joined: Jul 2004
    Posts: 1,844
    Likes: 73, Points: 48, Legacy Rep: 608
    Location: Duluth, Minnesota

    Steve W Senior Member

    I wouldnt use any plywood made in the USA in any part of any boat,period,we only really have one standard,BAD. As Wynand said,use BS1088, it really is not that expensive in a small boat and is a pleasure to work with instead of a frustration and you can end up with something you can be proud of. Unfortunatly you wont be able to buy it locally so will need to order it and the shipping is not cheap.
    If you absolutly must buy local,skip the US junk and buy Baltic birch(not just birch) Baltic birch has many plies,exterior glueline ,no voids fairly clear face veneers,it is very well constructed.As for resistance to decay,that is species related and has nothing to do with the grade, Birch is rated as non durable,the same as marine grade Occume Baltic birch is available at our local Menards lumber yards in 1/4", 1/2" and 3/4",i dont know about Home Depot or Lowes, this is what the good underlayment that Ecflyer recomended a few posts up.
    Steve.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.