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. KD8NPB
    Joined: Mar 2018
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    Location: South Carolina

    KD8NPB Junior Member

    ATC Polyfair F26 is my preference.

    Rough shaping, Sand up to 120
    spray up with 707-002 primer
    Sand up to 180
    904-046 black Topcoat.
    Sand up to 1500 moving to wet sanding after 400, then buff
     
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  2. Steve Clark
    Joined: Jul 2004
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    Location: Narragansett Bay RI

    Steve Clark Charged Particle

    I think you will regret using foam for the reasons stated and because it is a poor substrate, not stiff or stable enough for the fairing process. You can end up chasing your tail. However, you seem intent on your process and seem resistant to suggestion. I have tooled more than a few boats, but never mind.
    Commercial, pre mixed fairing pities have the advantage of consistency. Multiple batches will sand and shrink consistently, which helps when long boarding. If you want to mix your own, it is best to have a recipe which you use to make your batches. I prefer a 2:1 ratio of Red Microballons to Cab-o-sil ( flumed silica.). I blend with a flour sifter.
    Polyfair is a very good fairing putty which is cheaper than gallon cans of Bondo and formulated for this kind of work.
    Continuous stand Matt is usually for resin transfer operations and is not appropriate for open lamination. .75 ox mat is ok for using in between layers of roving, but 1.5 oz mat is cheaper and builds thickness faster. You are less likely to have the roving print out on the tooling hell if you first laminate 3 layers of 1.5 oz mat and let it kick. Laminating an 18’ sailboat mold will take quite a bit of time, particularly if you have limited experience. Find as many things to build out of fiberglass as you can before you start on the hull mold.
    The way to figure out what the mystery roving: cut a square yard and weigh it on a small scale. Chances are it will be 17 or 22 oz/yd^2 .
    Be careful of picking up “deals.” Any of this stuff that doesn’t work the way it ought to can trash all the work you put in.
    SHC
     
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  3. John Merritt
    Joined: Oct 2018
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    Location: Ada, MI

    John Merritt Junior Member

    KD8NBP and Steve, Thank you very much for your input and help. After reading you post about the stability of foam as a substrate I am going to try " planking" the plug ( from keel to sheer) with strips of either 1/8" hardboard or plywood instead of the foam. Hardboard might be to brittle for the tighter curve at the turn of the bilge. I will do some test strips. Thanks again.
     
  4. Steve Clark
    Joined: Jul 2004
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    Steve Clark Charged Particle

    Good choice.
    I forgot to mention the most important reason not to use pink foam. Heat.
    When building up mold thickness the laminate gets quite hot. All resins are exothermic, and give of heat as they polymerize. You need a mold that won’t melt, shrink or warp under this heat.
    SHC
     
  5. John Merritt
    Joined: Oct 2018
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    Location: Ada, MI

    John Merritt Junior Member

    That's good to know... and brings up another problem. This boat is designed to be beached.. and as such the stem will have a large radius ( 2" - 3").... my Rhodes 19 has a sharp bow and the gelcoat /fiberglass is quite chipped up from beaching. But forming this rounded stem seems quite a challenge. I had thought about filling that front compartment ( the triangular space from the stem to the first station) with 2 part foam before planking and fairing the plug and then literally cutting off the first 4" of the plug with a chainsaw and the rebuilding the now rounded stem with yet more 2 part foam. For sure not the most elegant solution but the best I can come up with.... any ideas ? will 2 part foam stand up to heat ? Thanx.
     
  6. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    What will you pour the foam into if it isn't planked yet?
    Then what will you pour the second batch of foam into?

    I fore see a larger glob of foam on your shop's floor.

    If you're redesigning the bow, now is the time to cut it away and reframe.
    If you are having difficulty bending battons to your frame, then plane the battons thinner and use multiple layers of battons to achieve the desired stiffness.
     
  7. Steve Clark
    Joined: Jul 2004
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    Location: Narragansett Bay RI

    Steve Clark Charged Particle

    Wood shapes very easily with a 36grit disc on a 5” grinder. There are catalogues full of other well developed wood shaping tools that aren’t quite so brutal.
    If you aren’t concerned with structural integrity you can stack wood up and beat it into submission every bit as casually as you spread putty. Just think of it as 40 lb. density foam.
    SHC
     
  8. John Merritt
    Joined: Oct 2018
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    Location: Ada, MI

    John Merritt Junior Member

    Update. The hull plug is now completely planked with underlayment plywood. I planked her keel to sheer with strips about 3 1/2 " wide and about 5 mm thick on 3/4" x 3/4" longitudinals spaced about 6" apart ( stations were about 18"apart). If I had to do it again I would tighten up the spacing of the longitudinals to about 4" apart for better stiffness. Steve, thank you again about you advise against foam.... that would have been a huge mistake!

    My plan at this point is to cover the hull with 1 or 2 layers of CSM as a base for the fairing putty. I believe ( and please correct me if I'm wrong) that the resin for the CSM coat should be mixed without wax.... so that the putty will adhere. ? Or should it have wax added and then be sanded?

    For fairing putty, my plan is to start with 4 parts microballoons / 1 part cabosil and add resin to peanut butter consistency. Then add MEK to putty as needed. Does this sound about right? I plan on putting on a first coat using a serrated trowel for easier fairing and then going back with a second smooth trowel to fill in the gaps. Do I need to add wax to the resin in making the putty for the first coat ? Second coat ? Both ? Neither? Since the first coat has to be sanded , my understanding is that wax should be added so it doesn't "gum up " the sandpaper.... True? Thank you in advance, John.
     
  9. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    It sort of depends on the exact resin but...

    Never ever, if at all possible add wax to gel coat or resin.

    Only add it to the final layer if you know you are done and it’s absolutely needed.

    With the blend of fillers you plan to use gumming won’t be an issue unless you’re in a big hurry.

    The first part of the fairing will be with coarse grit, so clogging shouldn’t be a problem, wax will be.
     
  10. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Senior Member

    @John Merritt do you own a camera? :D

    Interested to follow along, but pictures would help. I recently made an extended swim platform using the plug/mold/part approach. I used the pink foam boards as a base/frame for the plug and coated it with fiberglass/epoxy.
     
  11. John Merritt
    Joined: Oct 2018
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    Location: Ada, MI

    John Merritt Junior Member

    For those interested I am attempting to add some photos of the plug build..... KIMG0179.JPG KIMG0179.JPG
     

    Attached Files:

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  12. John Merritt
    Joined: Oct 2018
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    Location: Ada, MI

    John Merritt Junior Member

    Next question... although I'm not there yet. For the mold itself, would it be possible to use regular laminating resin (instead of tooling resin) AFTER tooling gelcoat and a few layers of CSM with tooling resin OR is it important that the whole mold be made using only tooling resin. Thanx.
     

  13. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Will it work, yes, but what you use depends on how well you want it to hold up long term.

    Tooling resins come in various types and styles, from a rigid ISO, to low shrink VEs, the better the resin and attention to detail, the better the chance the mold will hold up long term.

    But there is no requirement to use an official tooling resin, a standard DCPD blend will get you about 80% of the way there, even closer depending on the exact resin.
     
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