Wood for first skiff build

Discussion in 'Boat Design' started by Albert Jr., May 27, 2013.

  1. Albert Jr.

    Albert Jr. Previous Member

    Summer vacation is almost here, mine starts 14th of June.
    I am thinking of doing a skiff build with a friend of mine and I found a whole bunch of perfectly cut plywood strips that are collecting dust.

    They aren't marine grade which brings me to the question.

    If I fiberglass the outside and inside of the hull using thin to med/thin layers of fiberglass (2-3 layers) and make all nice and smooth by putting epoxy over it,
    can I than safely say that it won't rot and can I than sell the boat without any second thought ?

    The boat will be around 15 feet, I am thinking of putting 2 layers of plywood and we're thinking of powering it with a 89' merc 25 hp.

    I already have the plans and I've adjusted it a bit to make the boat wider and a little nicer looking.
    Stringers will also be non-marine grade woods.
     
  2. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    If you use non-marine plywood you should never say it won't rot.
    But fiberglass and epoxy will protect it as long as the glass/ epoxy doesn't get broken or scraped off, and the wood is completely sealed to begin with.

    Lots of people have used non marine and kept their boars for a long time. Actually Marine plywood does not guarantee no rot, just that the glue will hold together when wet until it does rot. Also Marine has "no" voids on the interior plys, so it is stronger.

    If you want comments about using non-marine ply you ought to show a picture or a scan of the plans so everyone knows what you are talking about.

    Stringers would be better as solid wood, narrow pieces of ply have very little bending or compression strength. Try breaking an equal size of solid wood and plywood. You won't want to use plywood. The strength of ply will be about 1/2 of solid wood, if there are no voids.

    Plywood boats with figerglass skins are really fiberglass with a wood core. The glass will provide most of the strength and stiffness assuming the plywood is not real thick. If the ply is thick, you might as well just use 1 ply glass inside and out. Any more will be wasting money, generally. Except on the keel line where it will protect from scraping.

    Good luck

    Have fun.
     
    1 person likes this.
  3. Albert Jr.

    Albert Jr. Previous Member

    Wow, didn't expect this good an answer this quick.
    About the stringers, when I said non-marine grade wood, I meant solid wood (didn't know they use that)
    Another thing I was thinking was using divinycell for stringers but that'll have to wait for another build.

    The ply measured is roughly 1/2'' thick, this is why I want to put 2 layers.

    I do have a picture but that is of the original design and I'll have to find a way to resize it.

    For those who are interested in 'free' plans...
    It is literally the MOST basic design available.
    Its drawn like on of those cars that preschoolers draw.
    This is why I've redesigned it, hope it works out because I am not professional.
     
  4. Albert Jr.

    Albert Jr. Previous Member

    Here she is.
    Words are in Dutch. :D

    Note that this is the original drawing.
     

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  5. Petros
    Joined: Oct 2007
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    Petros Senior Member

    two layers of 1/2" thick plywood will make a very heavy boat. One layer should be good enough. I am not sure there is such a thing as "non-marine" solid wood, almost anything and everything has been used to build boats, even bamboo. Any reasonably clear, reasonably tight grained wood can be used for all the solid sawn lumber parts, if it has high rot resistance than so much the better. though rot resistance it is not a requirement for smaller boats that will spend most of their time out of the water when not in use.

    You should test the glue in the plywood you have for being water resistant. There are some simple tests you can do, like boil a piece of it in water for a hour and than let it dry over night and see if it laminates. If you do a search on the internet you can find the specific procedure for doing a boiling test for water proof wood glue. All exterior grades of construction plywood should have water resistant glues, if it is an interior grade or ungraded, chances are it is not water resistant.

    Non-marine grade plywood can be used with some care on a small boat like the one you are proposing. Select pieces that have little to no voids in the edges, and than seal all the cut edges with epoxy before you assemble the boat.

    I am not sure I would build that boat you posted, unless you have an example of one and you can use it and find it acceptable. There are other free or low cost boat plans available with much more detail and of more modern design. do a search for free skiff plans.
     
  6. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    Two layers of 1/2" ply is going to be massively thick for most hull areas. 1/2" would be more like it, though one can't tell from that drawing.
    Using cheap construction plywood is possible if the plywood is of decent quality though skinning with glass isn't normally necessary for all but the joints. Plywood is strong enough to use it alone without adding epoxy or glass.
    The transom especially is a bad place to use cheap plywood due to the voids within the core that can hold pockets of water which will slowly rot the area involved, never mind the fewer thicker plies found in the cheap stuff.
    You should take a sample of the plywood and boil test it to see if it comes apart (boiling accelerates the delamination process). Who knows if the glue used in the plywood is going to hold up.
    Find the correct thickness of plywood to do the job right. Having to laminate two layers is absolutely false economy. Price epoxy and see.
     
  7. Albert Jr.

    Albert Jr. Previous Member

    Alright, thanks guys.
    I'll boil test the plywood and I'll look for some more skiff plans.

    Thanks again.
     
  8. messabout
    Joined: Jan 2006
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    messabout Senior Member

    Yes, do look for other skiff plans. The one posted appears to be a real fatty. I'm not so sure I like the plan view. Conventional planeing skiffs have the transom about the same width as the main frame.
     
  9. Albert Jr.

    Albert Jr. Previous Member

    I tried searching for some plans (free plans) but haven't found any.
    Can anyone help me out ?
     
  10. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

  11. Albert Jr.

    Albert Jr. Previous Member

    AlrIIght :)
    Thanks man.
     
  12. Albert Jr.

    Albert Jr. Previous Member

    Btw, do you think it can hold a 25 hp ?
     
  13. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

    There are 4 plans there. Are you interested in the one that is about 15'? if so yes it will handle 25 HP
     
  14. Albert Jr.

    Albert Jr. Previous Member

    Alright thanks a lot, just what I needed.
     

  15. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

    Glad you like the plans. Tomorrow I will check the plans and the size of the materials used in the transom to see is you need to "beef it up a bit." I printed out all these plans for my library and everything is there and simple to build.
     
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