Boat Lumber Moisture %??

Discussion in 'Materials' started by abosely, Jul 24, 2015.

  1. abosely
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    abosely Senior Member

    What moisture % is recommended for boat building lumber?

    Everything will be completely encapsulated in 4 coats of epoxy and varnished or sheathed in fiberglass.

    Most of it will be 1" thick and 2" or 3" wide, some will be up to 10" wide for laminating keel.

    I'll be cutting & drying the lumber. So not sure exactly how low I'll be able to dry it. Interior furniture wood seems to be brought down to about 8%. Not sure but don't think that low of moisture it wanted for boat building.

    Humidity here is usually in the mid 60% to upper 70%. I'll be drying it in a black plastic 'tent' a couple feet off the ground & with vent holes in top (protected from rain getting in$to let moisture out, and have fans circulating the air in 'tent'. Of course the wood will have 2" stickers for air circulation & foot or so around all sides of lumber.

    But I don't know down to what moisture % it should be brought down to.

    It will be rough sawn ⅜" or so oversized and planed to final thickness of 1" & correct width after drying. I can let it acclimatize under cover for couple weeks before building with it also.

    It's for a Wharram Narai Mk IV.

    Cheers, Allen
     
  2. PAR
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    PAR Yacht Designer/Builder

    15% is as high as you can permit, for epoxy to work well, but all epoxy formulators will recommend 12%, likely to offer some fudge room within the piece.

    If there's a local self storage facility near you, get a box big enough to sticker you lumber up. Place a box fan or two to blow air through the stickered stack(s) and close the door, for a few weeks. Of course you'll want to rotate and turn the stock, which is tedious, but will expedite the drying process. Check the moisture content after a week in the tropical sun, inside an uninsulated metal storage box. Might as well rotate the stock at this time too. A dehumidifier can speed things up too.

    For laminates, try to keep them 1" or less in thickness to prevent internal stresses from causing issues. This is especially true of hardwoods.
     
  3. Jamie Kennedy
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    Jamie Kennedy Senior Member

    PAR,
    How low can you go without getting into trouble with checking or other issues? Say you are working on something reasonably small and are looking for better performance for weight. Can you go less than 8%? Does it help to dry more slowly, and if so, how slow?
     
  4. gonzo
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    gonzo Senior Member

    At 8% it will be difficult to bend. Checking depends a lot on the species. What kind are you drying?
     
  5. abosely
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    abosely Senior Member

    Eucalyptus deglupta, also know as Rainbow Eucalyptus, & Kamarere.

    Cheers, Allen
     
  6. PAR
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    PAR Yacht Designer/Builder

    There's no advantage of going below say 8% or even 10% for that mater. Checking is going to happen for one of a few different reasons. I find checking is internal defect issue more so than a drying thing, though if lumber is dried too fast, you'll get all sorts of issues, along with checking.

    Species selection is a better way to go for weight reduction, not less moisture content, which doesn't have a big impact, once the stock is environmentally stable. Simply put stock with 15% moisture content isn't that much heavier than 10%.
     
  7. Jammer Six

    Jammer Six Previous Member

    Checking and cracking is not a function of how dry, it's a function of how it was dried, case hardening and time.

    Gonzo, I don't think he's bending.

    Gonzo's right, though, you want green wood (and then only certain species) if you're going to bend.

    I'd rather bend than laminate.
     
  8. TeddyDiver
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    TeddyDiver Gollywobbler

    Mostly time.. Fastly dried wood even if used in an environment with higher humidity will check with time.
    The following is just my reasoning and experience of allmost 50 yrs of wood working.
    When drying wood in the first stage the water in the capillars evaporates. Next dries the cell cavities outside the capillars. These dry out in days, weeks or months depending of the circumstances, wood species and thickness. Last to dry are the cell walls and they are the trickiest part of drying. Only a part of cell wall drying is related to water as they contain lignine, oils and other organic compounds. Drying time is counted in years..
     
  9. PAR
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    PAR Yacht Designer/Builder

    Jammer (surprisingly enough) is mostly correct, but it's also true that rapid drying will also cause issues. In forced drying it's still the internal stresses within each piece that cause this, not the drying method, though some methods are harder on the timber than others.

    With proper technique, you can bend anything, though some species take to bending with a lower percentage of breakage. The easiest to bend is green stock, but it's not completely necessary, given a reasonable moisture content and some heat.
     
  10. Jammer Six

    Jammer Six Previous Member

    Hoadley, R. (2000). Understanding wood: A craftsman's guide to wood technology. Newtown, CT: Taunton Press.

    This book will change the way you look at, handle, dry, select, think of and work with wood. It is the most recent edition of a classic.

    Trying to explain what is in it here would be an exercise in frustration for all of us. You're either ready for it or you're not.

    If you want to know how to dry wood, select a drying sequence, method or species, if you want to know where the myths about kiln vs. air drying come from, if you want to know how to dry wood quickly without "issues", and if you want to double your game, get it and read it. Then work a few years, start cutting and drying your own wood, then read it again. You'll be surprised at how it's changed on your shelf.

    Warning, it is not light reading. It is not for someone with a passing, mild interest in wood. It's only for those who want to get good, and the author assumes you are literate.
     
  11. abosely
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    abosely Senior Member

    I'll check out getting it then. Sounds like my kind of book. I like technical, detailed reading.
    If I'm interested in something, I like to learn about the subject and understand it as best as I can.

    I know I'm weird, I really enjoy researching and learning about whatever I'm interested in.

    Cheers. Allen
     
  12. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The first edition of "Understanding Wood" (1980) and has long been a reference for many. After two decades, the revised edition, which in itself is now 15 years old still has value, though some finishing information isn't up to date, particularly in regard to acrylics, some of the urethanes and particularly the epoxies and LPU's, currently in use.
     
  13. Jammer Six

    Jammer Six Previous Member

    My first kiln was a solar kiln. That was a waste of carbon. I burned most of it after I tore it down. It didn't work, it annoyed me and my wife thought it was ugly. My second kiln was a contraption of lights and fans. That was a waste of electricity.

    My third and current kiln runs on a simple dehydrator. It has a lamp to kick start it, once it reaches about 95F, the lamp is turned off and the dehydrator takes over. Water is forced out of the wood by the heat. (Actually by the air's increased ability to hold moisture.) The dehydrator senses the increase in the amount of water in the air, and turns on. The water is sucked out of the air and pumped out of the kiln through a garden hose. The dehydrator is running, which creates heat. The heat keeps the air in the kiln at about 95 or 100. The cycle then repeats. It's elegant, simple, cheap and fast. Trying to dry wood by managing heat alone is a mistake. Both heat and humidity have to be managed.

    When I built it, I had rolls of insulation and caulking on hand, and thought I was going to have to insulate and seal the box to keep it running off just the heat of the dehydrator. What actually happened is that the interior of the kiln kept going over 110F or 120F, and I had to tear a bunch of insulation out.

    The problem is not how to force the water out of the wood with this kiln, the problems are managing the schedule of how fast to do so. It becomes managing when and for how long the dehydrator runs to keep the air dry and the temperature up. The questions are how hot and how dry. You can go from green to 8% in a week, but you won't be able to use it, for reasons explained in Hoadley. Guaranteed to create case hardening. Hoadley will explain more, and explain the need for different schedules for different species.

    How dry I make wood now and at what point in the process I do so is dependent on what I'm going to do with it.

    Balance the method against your purpose. There's no need to dry wood suitable for use in a piano in a boat. But there's no reason to wait three years for boat wood, either.
     
  14. abosely
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    abosely Senior Member

    I've been looking for some information about milling, drying & working with Eucalyptus deglupta/Rainbow Eucalyptus, the lumber is sometimes called Kamaere wood.
    But so far haven't found anything specific to deglupta.

    Does the book have information about Eucalyptus deglupta? There are several species of Eucalyptus and some are very different. From what I understand, Eucalyptus deglupta is quite different than most of the others in the Eucalyptus family.

    So if anyone knows where to find info about Eucalyptus deglupta, please let me know.

    Cheers, Allen
     

  15. Jammer Six

    Jammer Six Previous Member

    Don't know. The first time I read it, I was spalting Alder, which is a trash tree here, used for firewood. I was looking to start and stop the spalt reliably. After that, I was spalting, drying and using a lot of broad leaf maple, another trash tree here, and my concerns were more about the spalt than real drying. When I realized how much control cutting and drying my own wood gave me, I expanded the sequence to things I was doing professionally.

    Now I use a lot of the maple anywhere I want hardwood or Yellow Cedar where I don't. Most of my experience is with one of those three woods, other than the obligatory and ubiquitous red and white oak. I used miles of red oak milling and installing floors back when I was young. Real young. If I never have to use red oak again, I'll be a happy man.
     
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