Composite Rowboat

Discussion in 'Fiberglass and Composite Boat Building' started by Scott M.., Oct 13, 2020.

  1. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    People, please, unless the OP wants to walk on a waterbed SOF is unsuited for his purposes. By the time he fits a floor stiff enough to support him at any point the weight avantage is gone. This is true regardless of how strong or fragile you regard SOF construction to be.

    The simplest way to build the boat from the model is to use flat panels. Either premade ones or self made on a piece of melamine faced chipboard. With a big enough melamine surface one could even laminate the whole thing in one go and fold it up later. It does not get more "instant boabuilding" than that. 600gr/sqm of fiberglass on the outside is certainly enough for normal use and the ocasional abuse of such a small boat. The only question is how much surface area the boat has, and can he make his self imposed weight target. I think it is possible.
     
  2. Scott M..
    Joined: Oct 2020
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    Location: Newtown, CT

    Scott M.. Junior Member

    As you stated the final goal is a unique shape and weight savings.

    If I can't end up with a boat that is less than an aluninum rowboat, what's the point.

    I already own a 12ft rowboat but its more than 100pds.
     
  3. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Senior Member

    Just wondering what you will do as you are building and the weight of the boat begins to exceed your target weight? Scrap :eek: or keep going :rolleyes: . . . ?
     
  4. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    The thing to do here is to do a careful and thorough weight estimate first before he even starts building - it should be possible to get the estimate to within 10% of what the finished weight will be if one is careful.
     
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  5. Scott M..
    Joined: Oct 2020
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    Location: Newtown, CT

    Scott M.. Junior Member

    So my plan is going to start by taking blocks of pink foam board covered with boat heat shrink as a release film covered with polish. Spray Line-X to various thicknesses. This will help me evaluate weight and stiffness.

    Once I have the weight per sq foot by X thickness, I can then simply calculate the approximate weight of the boat. Then depending on the final method of construction determine the weight of any additional materials.

    If the weight turns out too high, I can look to modify my added materials.

    I'm also going to make the bench style seats removable.

    Finally if all else fails I will cut the front 4 ft off to make it a two piece boat and have flanges to bolt together the two parts.
    Scott
     
  6. Rumars
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    Rumars Senior Member

    Forget the LineX, it is just added weight. While it can be a waterproof and impact proof layer, it does nothing to stiffen a panel. You would still need to use fiberglass to achieve the needed stiffness. It would only be useful if you would make the lightest sandwich panel possible and use LineX as abrasion protection. But while it may hold your panel togheter after an impact, the underlying panel would still be shattered, and now even harder to repair.
     
  7. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    A word of caution Scott - in this section of the webpage for Line-X they mention 'Unmatched abrasion and impact protection' - which basically means that the material is good in compression..
    LINE-X for Manufacturers | LINE-X https://linex.com/line-x-for-manufacturers
    But what about in tension?
    The hull surface of your boat is going to have areas in tension - one area especially will be the floor when you are standing on it - hence it might be worthwhile making up a sample of the thickness that you intend to use for your hull, and applying a tensile load to it by trying to stretch it.
    And see how strong it is in tension.

    Edit - I just saw Rumars' note above - +1 re his comments.
     
  8. Scott M..
    Joined: Oct 2020
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    Location: Newtown, CT

    Scott M.. Junior Member

    First let me say the boat is going to be Line-X, not used as an abrasion coating and yes I will need to do something to gain stiffness across the floor.

    But let me assure you the LineX material when sprayed to 1/8 thick is strong, very durable, and light but relatively stiff.

    During testing at work, I took a 6" X 10" x 1/8 thick piece, folded it in half, put it in a vise and crushed it by hitting the vise handle with a hammer. Took it out and bent it back flat and it had no sign of stress, cracking, thininng, etc.

    So trust me I have done enough testing to know this material will easily be able to be made into a boat.

    The only issue is creating stiffness across the floor and the best and lightest way to do that.

    Also remember that the bench seats which go from side wall to side wall will stiffen up the sides and the floor.

    Yes will there be some flex, most likely, but once it is all assembled with seats it should be minimal.

    Remember that a carbon fiber made canoe with no core also flexes a considerable amount.

    As for repair if its ever even necessary, you can temporarily patch it with an adhesive sealant and then when you can you can have the area reshot with LineX.

    Remember that LineX is sprayed on at an elevated temperature to allow it to bond to any subsurface and to bond to itself. So you can go back years later and still fix it.
    Scott
     
  9. Scott M..
    Joined: Oct 2020
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    Location: Newtown, CT

    Scott M.. Junior Member

    I also am planning to put 2 V shaped ribs running approximately 10 feet long equally spaced from the center which will provide stiffness and help the boat to track better in the water.
    Scott
     
  10. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Any 6 10 inch piece of material that can be folded into a vice is NOT still enough for a single skin boat!!!
     
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  11. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    I'll save you some trouble, polyurea (wich LineX is) has a density of 1000-1250kg/cum (depending on the exact formulation). One square meter, 3mm (1/8") thickness, weighs 3-3,75kg. Anything you use to get a floor rigid enough without feeeling like standing on a waterbed will add at least 1kg/sqm (this includes honeycombs).
    The problem is 3kg/sqm (0.6lbs/sqft) is more or less the upper limit in order to fit into your self imposed weight limits. So you either reduce the total square footage of your boat or you reduce material weight.
     
  12. Scott M..
    Joined: Oct 2020
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    Scott M.. Junior Member

    I agree, once I verify the weight, I may make the decision to make it a 12ft boat to be closer to my target weight or I may make it a two piece boat.

    Shoot I may even decide to make three pieces so I can have either a 12ft boat or a 14ft boat depending on what my use will be at the time.
    Thanks
    Scott
     
  13. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Seems to me that a two part (or even a three part) dinghy is your best solution in the given circumstances.
    And with the weight of a LineX hull probably being in the same ballpark as a ply / epoxy hull, then it would be sensible (IMHO) to stick to proven technology and build your boat in ply / epoxy.
     

  14. Scott M..
    Joined: Oct 2020
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    Location: Newtown, CT

    Scott M.. Junior Member

    Thank you for your comment but part of this experience is to do something that no one else has tried.

    That is part of the fun.

    This is not just about the finished boat but the level of satisfaction you get from creating something that is one of a kind.
     
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