new dinghy mold

Discussion in 'Boat Design' started by dan catalyst, Aug 5, 2013.

  1. SamSam
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    SamSam Senior Member

    You can find and enlarge this chart ....

    [​IMG]

    on the third post in this thread ....

    http://www.boatdesign.net/forums/fiberglass-composite-boat-building/fiberglass-thickness-8686.html

    It will give material thicknesses and amounts of resin needed for them. Resin weighs about 9 lbs a gallon.

    Your proposed layup seems a little thin, but if it is you can always add more where you think it might be needed.

    Resin is like paint as far as price, if you buy 4 single gallons you might as well buy a 5 gallon bucket as the price is the same.
     
  2. dan catalyst
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    dan catalyst Junior Member

    oh great! thanks for that. i know it needs to be apox 1/8th thick and weigh about 70 lbs to be strong enough.latest news is i shopped around and found affordible epoxy. im going with two layers of 1808 overlaped down the skeg and transom. these two threads are starting to move in the same direction, so lets move the laminating descusion over to here http://www.boatdesign.net/forums/fi...ding/layup-recomendations-8-dinghy-47888.html.....
     
  3. wayne nicol
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    wayne nicol Senior Member

    use roller!!! not just brush's
    consider spraying the gelcoat, would be easier for the skeg area.
    still dont know why nobody has developed an aerosol can of mix as you spray gelcoat...

    i sure love this warmer weather we are getting:rolleyes:
     
  4. FAST FRED
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    FAST FRED Senior Member

    Have no idea why you fear the use of a chopper gun , in good hands they are great.

    However the chop gun will also shoot just catalyzed resin which is far less messy than 1 gal pails and a good roller.

    The use of cloth will remove the fear of roving imprinting thru the surface coat.

    A dinks get hard use , dragged up beaches , I would not use gel coat , just quality modern paint for the finish ,so an owner can repaint.
     
  5. wayne nicol
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    wayne nicol Senior Member

    chopper guns can give a mix that is too rich in resin, hand layups can have far better control over this.
    based on my experience, if you are going to make a few, i would vacuume bag them, faster, way cleaner, no air voids etc, and a great resin to glass ratio.
    we made a very affordable system for doing kayaks many years ago, that was made from simple parts, no fancy peel plys etc etc

    but if youre only gonna make one or two, then why bother with the setup, a brush and a few different size rollers.but spray the gelcoat- makes a huge difference to the quality of the layup.

    gel coats protect against hydrolysis, and offer uv protection, thats why most small open craft are painted/sprayed with a waxed gelcoat on the interior
     
  6. dan catalyst
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    dan catalyst Junior Member

    i was under the impression if i make the boat out of epoxy, i cant gelcoat the inside.
     
  7. rwatson
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    rwatson Senior Member

    If you build the boat out of epoxy, you dont NEED to gelcoat the inside, or outside.

    There are epoxy gelcoats, but normal Polyester Gelcoats wont adhere all that well to an epoxy surface, inside or out.

    paint for epoxy dinghys is a good idea, as its much easier to repair on a regular basis than gelcoat - after rocks scratches etc
     
  8. SamSam
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    SamSam Senior Member

    What did that consist of? Were you doing wet bagging or infusion?
     
  9. wayne nicol
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    wayne nicol Senior Member

    a vacuume pump from an automatic milking parlour- which we had to re-do, the most expensive part, that was plumbed to a "vacuum pot"- a seperate steel cannister, that would trap any expelled resins, so they wouldnt be sucked into the pump- it was an old propane tank cut in half- with a flange welded on and a flat steel lid, with a rubber gasket seal, that was plumbed to the mold, large ice cream tup in the trap.

    the molds, were built with a substantial lip to them, about 4 ", and barbed hose nipples were threaded into these flanges on the outside of the mold- which was attached to the line from the "resin trap".

    after the mold was pulled from the plug, we laid and temp. glued a piece of surgicalk tubing around the perimeter- roughluy in the middle of the flange, we filled up around the tube with thickened resin, ( in the undercuts) and while it was green, glassed over the tube.
    when cured, we cut along the ridge of this mound, into the tube, and ground the mouth open a little bit- not too much, you still want a lip, pulled out the remains of the surgical tubing, we now had a nice slot.

    layup procedure-little bit of trial and error here with resin volumes, keep records!!!!
    gelcoat, dry, lay up the cloth- we used patterns for all our woven cloth layups, pour in the catalyzed resin- we liked using viny ester resin, we used a very heavy duty plastic we just bought on the roll- maybe equivelant to vapour barrier used in a house- we dont use vapour barrier in south africa!!!

    lay the plastic in the mold tuck it into the slot around the perimeter, stuff in some newsurgical house into the slot, and inflate the hose( need to make some adjustments for the "T' connection etc- use some clamps to hold the 'T in position- so it doesnt pop out if it wants too,
    you now have a tight seal, start the vcac pump, and start squuegie'ing the resin around, pulling the excess up to the vac lines, and letting it go to the trap.

    we had enough "leaks in our system, we didnt need vacuume release valves, etc etc
    we just let the pump run until the resin kicked.
    no peel ply( hard to get in africa- and then very expensive!!) yes the plastic does leave wrinkles in the interior, and sometimes the plastic folds will trap some resin, and make things tough, but nothing an angle grinder with a sanding disc and some finess cant deal with!!- its all inside a kayak.

    clean up takes a bit longer, but lay up is much quicker, and the quality is much better than hand laid, for that job,
    i would pour the resin all down the "keel", not just in a blob, then just pull it up the sides.
    we used screen printing squeegies, and just shape the sharp corners off- a slight elliptical shape on the ends- kinda want to match the average profile of the mold!!
     
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  10. SamSam
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    SamSam Senior Member

    Thanks for the reply. I had a similar 'generic' set up, hooked up to the vacuum side of a refrigerator compressor, same kind of lumberyard plastic from a roll sealed on the edges with some commercial window setting caulk on a roll and a throw away overflow box made of 3/4" plywood, screws and liguid nails with a 1" disc of plexigas set in the top to see if it was getting too full to use anymore. The 'unit' was plumbed with pvc pipe, downstream of the overflow box was a vac guage, then a tee'd in water hose faucet for vacuum release and adjustment, then the compressor. Hard enough not to collapse flexible plastic tubing connected the overflow box to the project which connected to the same stuff slotted and taped around the edges of the plastic vac bag. I think the whole thing was made with stuff laying around, it probably cost about 25¢ for the whole thing. It would draw to 26-27 inches of vac, more than I needed.
     
  11. wayne nicol
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    wayne nicol Senior Member

    good job SamSam, even simpler than ours.
    what were you building!-sorry dont mean to hi-jack the thread.
     
  12. SamSam
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    SamSam Senior Member

    At one time I made canoes mainly, but didn't make the vac rig until later, so it was used in various fg jobs and woodwork.

    I don't know if it's really hijacking the thread as it might be a possibility for this dingy in the OP. The deep skeg might be a problem, but it could probably be worked out.
     
  13. wayne nicol
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    wayne nicol Senior Member

    we also made very high end carbon and/or glass kayaking and rafting helmets.
    the two part mold was built with a flange all around it, and a glass " lid" was made.
    gelcote, and glass layup(weave only) with rough and quick saturation- to a fixed recipe!, mainly to hold glass in place, latex bladder inserted, lid clamped on- with laid in quick release clamps, and bladder inflated to predetermined pressure.squuezed out excess, followed complex contours easily.
    we probably had about 20 mold at the end- cheap and very very effective.- can mix a wee bit hotter and not be too worried about chasing time- just not too hot , so as to effect the layup negatively- if started early- could get two pulls aday from each mold!- lay up time, 2 to 3 mins- with precut glass panels. and we only used a hand pump- automotive pump- Africa man!!!
    different shapes of latex bladders can be made up with sheets of latex glued together - i believe- but we never needed to do that.

    Voila-Our "pressure bagging system"!!!!

    maybe something could be done like that for the skeg.

    other alternativer: three wedges that combined make up a male interior mold of the glassed up skeg.
    wet out cloth, insert the two outer wedges- which are thin end up, insert third wedge , thin end down, between the other two wedges( in the middle!)as it is pushed down it widens out the (well waxed ) outer wedges- then vac bag over the whole show- the vac bagging will pull the wedges down and in.

    i would have a recess in the center wedge- with a hidden rope handle- that can be smoothed over with modelling clay, so after layup, clay is removed and wedge can be removed "easily".

    had these types of thoughts for some products we were developing, but never did any. but did all the research, and can pass on some more technical info if needed.

    cheers
    wayne
     

  14. SamSam
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    SamSam Senior Member

    Those are solutions. I was researching patents once and was amazed and made aware of how crude and rustic and Rube Goldberg like some primary solutions can be. Much as I hate the term, they're in the vein of "Get R Done" and they do work and are the best solution until someone comes along and refines it or has a different, better idea. Some primary solutions are the best though and cannot hardly be improved on.
     
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