Plywood

Discussion in 'Materials' started by Jakegator, Jan 19, 2012.

  1. Jakegator
    Joined: Jan 2012
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    Jakegator Junior Member

    hello, I know this is a somewhat over asked question but i couldnt find a thread that answered it well. Im building a much larger boat than usual, it will be a 40 ft glen-l sail boat for marine liveaboard. It will be built with the cold molded plywood method. so the plans call for 2 opposing layers of 1/4 inch ply. I have built many boats before that are part time on the water and used in some cases far below marine grade plywood. I am trying to save as much money as possible of course. So the question is what wood can I use there is resonable decent wood at the hard wear store for 21$ an occasional not but stable, I used it a few times for the part time boats and no leaks. I need to know what wood do you recomend me using? It will be fiberglassed over inside and out, and would appreciate opinions from either people who used different wood or no of people who did.

    Ps. I understand the "science" behind the types of wood and okume, launa and so forth, I simply will not pay that price.

    Thank you for your opinions and help!

    jake
     
  2. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    For a 40' boat that will live in the water.... If it isn't marine grade I wouldn't even consider it. You said you understand why they are more but won't pay that price... That's fine, but then you are going to build a boat that will be rotten and need replacement in 10 years. Seems like a lot of work and money pissed down the drain, but it's your money.

    I can't think of any alternative, or lower grade I would recommend for marine, below the waterline useage other than marine grade. Perhaps you could save a few bucks on non- cosmetic top layers, but that wouldn't amount to much.
     
  3. Tim B
    Joined: Jan 2003
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    Tim B Senior Member

    Boats have been made out of just about every practical material over the years, with varying degrees of success. So yes, empirically, you can use anything you want. However, I would strongly recommend that you do a cost study.

    There are two reasons for doing this:
    Firstly, it'll give you a ball-park figure of the total cost of your build. This will be useful to show what percentage of the build you can actually afford.

    Secondly it'll show you where you can save money. The hull skin in ply for this boat is probably less than 10% of the total cost, so your savings will be small relative to, for instance, buying plain bearing blocks instead of Harken Carbos; or finding a cheaper winch supplier.

    For what it's worth, the hull skin and structure is where I would spend the money. Without it you don't have a boat.

    Tim B.
     
  4. CatBuilder

    CatBuilder Previous Member

    Stumble is right.

    How many hours go into your build?

    If your boat has to get cut up and put in the dumpster in 10 years, are you really saving any money by using garbage materials in the hull?

    The hull is the LAST place you want to save money.

    Why don't you skip fancy electronics, upholstery, freezers, generators and those kinds of things instead?

    The idea is you want to skip things that you can buy later. You can't buy a new hull later. Build it right.
     
  5. Jakegator
    Joined: Jan 2012
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    Jakegator Junior Member

    OK thank you all, I do understand your point and I realise I did not word my question the way I wanted at all. I guess my main question is what grade can I get away with (AA, AB, B...)?

    sorry for the vagueness
     
  6. CatBuilder

    CatBuilder Previous Member

    You could certainly get away with a low face grade, but that's just more fairing work for you to do.

    They do make marine grade douglas fir, which will check and need glass over it in order to hold up nicely.

    All the marine grade I have seen (not that much, since I'm doing foam) is AA anyway.

    Others will have much more specific info on wood.
     
  7. lewisboats
    Joined: Oct 2002
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    lewisboats Obsessed Member

    Seeing as you are going to do two layers...why don't you use cheaper marine fir for the inner layer and the more expensive better ply on the outer layer? The cost of your base hull material is only going to be a 1/5th or less of the overall cost...but it IS what is holding the water out... after all...this isn't a 10ft throwaway boat. You are going to spend many many hours building it and for the grand or so that you would save using anything less... it isn't worth it to me.
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Jake, you need to log onto the APA web site and get some education about plywood grades and panel construction practices.

    The AA, AB, etc. designations, are the quality of the surface veneers and by no means an indication of the adhesives employed or worse the panel's construction.

    The reason you don't want to use a construction grade of plywood is several fold. The biggest issues are strength and stiffness, coupled with construction flaws. For example a 1/4" sheet of marine grade BS-6566 or 1088 will have 5 veneer layers in the panel and you will not find a void at all in the 1088 panel, though maybe a very small one in the 6566 panel. Compared to a construction grade 1/4" sheet, you have only 3 veneer layers and the single internal layer will be full of defects, voids, overlapping veneers and other construction issues. This isn't a problem when hanging on your bathroom wall, but is a real big problem when dynamically loaded, such as seen in a boat. Construction grades are generally about half as strong as good quality marine grades (such as BS-6566 or BS-1088).

    The boat you've selected is a bit of a pig, but will make a reasonable live aboard. It's a dated design and much better is available, but if you love it, then go for it. As a rule, the planking and structural elements in a boat, are some of the finest wood used in it's construction. The reason is simply obvious, it keeps your socks dry. If you want to skimp on the planking and structural elements, then go for it, but it wouldn't be much of a savings in the big picture of the project. You might save 3% - 5% over the total project cost, but you'll have weaker and inferior planking too. The choice is yours. You can pay for it now or later, when you wonder why things are leaking, breaking or not able to tolerate reasonable use.
     
  9. WhiteDwarf
    Joined: Jun 2011
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    WhiteDwarf White Dwarf

    It used to be said, "If you have to ask how much, you can't afford it." Its a brutal truth, but in sailing it is a truth that can save your life.

    Jake, have you considered building a smaller design with first class materials? In building, you are putting a whole lot of your being into the craft. Would you accept second best?

    I wish you well with your project, but use the best materials for the hull. You can replace plain kit with better, when you can afford it, but you can't really do the same with the hull.

    Again, good luck
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    True, but that is why I won't go out in any boat that can sink. Pack with foam and if the worst happens and the structure fails, it is more a nasty inconvenience than an emergency.
     

  11. cappedup
    Joined: Jan 2012
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    cappedup New Member

    I'm guessing you have the job to build and sell the boat and want the best profit margin. Close?

    In which case, there is no answer.

    You wouldnt put all that time into your own boat, to sit in it and think about the quality of ply you used.
     
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