Plug and Mold for 18' sailboat

Discussion in 'Fiberglass and Composite Boat Building' started by John Merritt, Oct 1, 2018.

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  1. John Merritt
    Joined: Oct 2018
    Posts: 23
    Likes: 1, Points: 3
    Location: Ada, MI

    John Merritt Junior Member

    PLUG
    I have started building a plug for an 18 foot round bilge centerboard sailboat of my own design. I have cut out 15 stations from OSB which I will mount on a strongback. Over these stations I plan on afixing 1" x 1/4¨ wooden strips on about 3¨ centers which will run from stem to stern. Over these I plan on afixing 1/2"pink foam (from Home depot) planks about 3"wide that run from centerline to sheer. Then a single layer of light fiberglass cloth in epoxy for rigidity and as a base for a layer of bondo. Then bondo... sand, Duracoat... sand... buff....wax.

    MOLD
    The mold is to be 2 part . Build will be : Tooling gelcoat... 2 light veils, plain coat of resin and then a mix of 2 oz CSM and perhaps layers of heavy WR to required thickness.

    Questions:
    1. I bought some WR on craigslist but need some insight on exactly what it is. The packaging on the roll says Owen Corning Technical Fabrics LT 1140/S50/3040/25. What is the weight and type and would it be suitable for such a project?
    2. Would 0.75 oz continuous filament mat work as a veil for the mold (not is it ideal... but would it work and preclude print through) . Also, my understanding is that WR should be alternated with CSM in a hull laminate.... to keep weight down would a lower weight CSM (say 0.5 oz or 0.75 oz CSM ) be better than a heavier CSM. Would the same 0.75 oz continuous filament mat mentioned above work between the layers of WR?
    3. Any aprox guess about how thick such a mold should be to be long lasting and and quess about how much it would weigh.

    Thank you in advance for any and all help and input. John.
     
  2. Blueknarr
    Joined: Aug 2017
    Posts: 730
    Likes: 129, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    Welcome to the forum

    Some quick thoughts about your proposed plug.

    PLUG
    I have started building a plug for an 18 foot round bilge centerboard sailboat of my own design. I have cut out 15 stations from OSB which I will mount on a strongback. Over these stations I plan on afixing 1" x 1/4¨ wooden strips on about 3¨ centers which will run from stem to stern. Over these I plan on afixing 1/2"pink foam (from Home depot) planks about 3"wide that run from centerline to sheer.
    The pink foam is murderous to fair.
    Then a single layer of light fiberglass cloth in epoxy for rigidity and as a base for a layer of bondo.
    You will need more than a single layer of light fiberglass.
    Then bondo...
    Bondo is polyester so won't adhere to epoxy, but epoxy with micro-balloons will sand, Duracoat...
    Duracoat is polyester as well, so same adhesion issues
    sand... buff....wax.

    MOLD
    The mold is to be 2 part . Build will be : Tooling gelcoat... 2 light veils, plain coat of resin and then a mix of 2 oz CSM and perhaps layers of heavy WR to required thickness.

    Questions:
    1. I bought some WR on craigslist but need some insight on exactly what it is. The packaging on the roll says Owen Corning Technical Fabrics LT 1140/S50/3040/25. What is the weight and type and would it be suitable for such a project?
    2. Would 0.75 oz continuous filament mat work as a veil for the mold (not is it ideal... but would it work and preclude print through) . Also, my understanding is that WR should be alternated with CSM in a hull laminate.... to keep weight down would a lower weight CSM (say 0.5 oz or 0.75 oz CSM ) be better than a heavier CSM. Would the same 0.75 oz continuous filament mat mentioned above work between the layers of WR?
    3. Any aprox guess about how thick such a mold should be to be long lasting and and quess about how much it would weigh.

    Thank you in advance for any and all help and input. John.[/QUOTE]
     
  3. John Merritt
    Joined: Oct 2018
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    Location: Ada, MI

    John Merritt Junior Member

    Thank you. I hadn't planned on fairing the pink foam... only the bondo. I had planned on using epoxy as the foam isn't compatible with polyester...If I sprinkled something like sand or a coarse sawdust on the epoxy before it cured would that provide an adequate bonding surface for the bondo ? Is the blue foam any better or is there another commonly available and cheap foam that could be used? What fabric in your opinion would provide adequate stiffness for the plug?
     
  4. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    How many copies are you planning to produce?
    Will they be foam or balsa cored?
     
    Last edited: Oct 2, 2018
  5. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    John you have cexercised the first of the several questionable premises. You are going to bust your hump to build plug and mould for a boat that you have designed yourself. I do not mean to question your qualifications for doing an original design..................but many a disappointment has been made by assuming or fervently believing that your design is somehow more appropriate than the proven designs done by experienced practitioners of the art.

    Tell us more about the particular design that you have in mind. Drawings and technical details would be appropriate. Not to worry, no one here is likely to rip off your original ideas.
     
  6. John Merritt
    Joined: Oct 2018
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    Location: Ada, MI

    John Merritt Junior Member

    Thanx for the input. I don't know how many copies... but am thinking of using Plascore honeycomb (factory is about an hour from me) or foam. I am especially interested if anyone knows the weight of the WR I mentioned and if 0.75oz continuous filament mat will work as a veil and as the layer between WR. The boat is designed to be beached (under perhaps less than optional conditions).... anyone have any thoughts about either design or material modifications from a more standard 18' centerboard sailboat?
     
  7. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    My landlord owns a prominent ski-boat factory. He recently added a new design to its line. $300,000 spent on the plugs alone. $2 million to splash the 1st sellable. Plugs and molds ate great for mass production, not so much for limited runs or one-offs. Have you looked into moldless building? Round bottoms can still be made.

    Have you experimented with skinning honeycomb? Or flexing it into your boat's shape?

    My opinion is that honeycomb is to fragile for regular boats. It won't beach in optimal conditions let alone less than optimal.

    My choice. If you use the same foam (honeycomb) in plug, you will know how easily it will conform to mold.

    Weigh one square yard. Googled it, looks more like +-45 bi-axial than woven roving.

    Common veil is .50 ox, .80 oz between woven cloth. Should be fine on mold.

    Haven't seen design to comment on it.

    If you haven't determined core and glass skin and done the structural analysis, then you are NOT ready to start building the plug!
     
    Last edited: Oct 3, 2018
  8. John Merritt
    Joined: Oct 2018
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    Location: Ada, MI

    John Merritt Junior Member

    Thank you for the quick reply Blueknarr. Due to the risks of holing the boat while beaching I was thinking that any core material used should only be above the waterline - that way if there was damage it would be easier to repair. I was planning to drive down to Plascore and beg, borrow or buy a sample so I could determine its ability to conform to the hull. If both are properly bonded, is foam stronger than honeycomb? If so, why is honeycomb used... or in what application is it best used. Thank you.
     
  9. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    I have guests over this evening. I will return tomorrow
     
  10. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    All cores or solid lamination can be engineered to be equally stiff. A relitively flimsy core needs thicker skins than one inherently stiffer.

    Solid is the heaviest and requires the most resin and any shape is achievable.

    Plywood requires the least fiberglass and resin but is susceptible to rot. Tight radii and compound curves are difficult. Uncrushable.

    Foam may or may not be lighter than plywood. Requires more fiberglass. Very easy to shape and repair if necessary. Great post catastrophe buoyancy.

    Balsa is lighter than ply or foam.almost as easy to shape as foam but rots much easier than plywood.

    Honeycomb has the potential to be the lightest. Makes awesome flat panels but is extremely difficult to flex into curves, especially if pre-skinned. Prone to failure in the bonds between honeycomb and skin. It will be the most difficult to repair after things go wrong.
     
  11. John Merritt
    Joined: Oct 2018
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    Location: Ada, MI

    John Merritt Junior Member

    In my experience... things always go wrong eventually..... which is one reason Iḿ not a fan of balsa. A friend of mine just had to rebuild about a third the deck on his 41ft sailboat due to rot in the balsa core. I don´t envision the need for any flat panels so it sounds like foam may be a better choice for the hull and deck. On an 18ft hull I would ¨guess¨ that 1/2in thick foam would be adequate/appropriate .... but as I also want the foam to provide some flotation... from a structural or manufacturing point of view would there be any disadvantage to thicker foam say 5/8in or 3/4in ?
     
  12. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    In my experience... things always go wrong eventually.....
    My experience is it goes wrong sooner rather than later.
    I don´t envision the need for any flat panels so it sounds like foam may be a better choice for the hull and deck. And a good choice at that.On an 18ft hull I would ¨guess¨ that 1/2in thick foam would be adequate/appropriate .... but as I also want the foam to provide some flotation... from a structural or manufacturing point of view would there be any disadvantage to thicker foam say 5/8in or 3/4in ?
    Always trade offs balancing benifits and disadvantages.

    In sandwich core construction, stiffness is partially achieved by inherent stiffness of the component materials and partially from the distance between skins. Given the same core and skin materials: a thin skins over thick core could be similarly stiff as thicker skins on a thinner core.

    So as the core thickness increases:
    • Core cost increase
    • Core flexibility decreases
    • Skins can be thinner
    • Skin cost can decrease
    • Overall weight can decrease
    • Increased post catastrophe buoyancy
    • Puncture resistance decreases
     
  13. John Merritt
    Joined: Oct 2018
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    Location: Ada, MI

    John Merritt Junior Member

    Got it. What is are the differences between CSM and continuous filament mat ?
     
  14. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Not enough for you to worry about.
    In woven or directional cloths fiber length is strength. Along with yarn diameter and thickness of cloth. The individual fibers are strongest in tension; so the straight laid fibers can utilize more of their strength than those corkscrewed.

    This is why non-woven fabric has been developed. It is very strong in the yarn orientated directions. Not so much in the cross ply direction. It is usually crafted in 1-4 layers of 0°,+45°,-45°,90°. I believe the Owens Corning cloth you have is an example of 0/90 bi-axial.

    The twisting non-linear construction of mat largely negates the benifit of super long strands. Most CSM fibers are 1-3 feet long. Extremely short fibers produce extremely weak CSM, so avoid mat made from fibers shorter than a foot. I describe CSM as equally weak in all directions. If used as primary cloth then it needs to be very thick. Its use with epoxy is discouraged; the binder holding it together doesn't always dissolve in epoxy thus preventing a full bond between epoxy and fiber. Some CSM is made with epoxy safe binder. All CSM is polyester compatible. Judicious use of CSM strengthen fiberglass lay up schedules.

    Traits of CSM not prevalent in other cloths:
    • Conforms to almost any shape
    • Squishes into rough or irregular surfaces
    • Blocks texture of heavy weaving from telegraphing or printing thru to final surface
     

  15. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Stop, don’t buy anything or makes plans yet, you need to understand the basics before venturing any further down this path.

    If doing hand lay-up on these parts don’t use continuous strand may, it won’t lay down.
     
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