Dinghy infusion challenges

Discussion in 'Boatbuilding' started by bedfordd, Dec 28, 2014.

  1. bedfordd
    Joined: Apr 2013
    Posts: 10
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    Location: San Diego

    bedfordd DonnieB

    I've been infusing small 8' dinghy sailboats (sabots/prams) for about 18 months and have a consistent problem with voids / spots where the glass is not wetting out next to the gel coat. I've now had to trash two boats as about 1/3 of the glass is dry and the other few boats have needed the gel coat chipped out of many spots, then wetted out, faired, re-gelcoated and polished - a ton of work... I've been using VE infusion resin for all boats.

    To reduce on voids I thought I'd go from the 28 Hg vacuum to about 18 to reduce pulling gas from the resin. I've also made a few changes to the lay-up, they've been:

    1. My best one
    Gel coat (thin and clear to see how well I did with core templates)
    stitched 20oz triax 0/90 - 45/45 cloth
    1/2" scored & perforated foam core
    same 20oz stitched cloth
    peel ply
    bag

    2. some dry spots on hull
    Same lay-up but 1/4" foam

    3. some voids to be filled
    Gel coat
    Biax 20oz 0/90 - CMS
    4mm Soric core
    20oz stitched triax
    peel ply
    bag

    4. More dry spots on hull requiring fairing of the hull
    Gel coat
    Biax 20oz 0/90 - CMS
    1/4" scrimmed/scored foam
    20oz stitched triax
    peel ply
    bag

    5. I thought the CMS might be compressed to keep the resin to move over the gel coat. But this boat was so bad I had to toss the 1st try. The 2nd try had dry spots on hull requiring significant fairing of the hull:
    Gel coat
    20oz stitched triax
    1/4" scrimmed/scored foam
    20oz stitched triax
    peel ply
    bag

    6. Just made this boat and checked it this morning. May dry spots (see attached photos) and will have to toss.
    Gel coat
    this surface veil to reduce print-though (maybe better wetting out?)
    20oz stitched triax
    1/4" scrimmed/scored foam
    20oz stitched triax
    peel ply
    bag

    Yeah, running out of ideas. Was going thinking of trying a Continuous Strand Mat next to the gel coat but that might add too much weight to the boat. Any ideas would be surely appreciated. You an see a time-lapse of boat #6 at http://bedfordboats.com/2014/12/sabot-hull-6/ - thanks!

    See attached thumb nails of 1) voids on the rails and 2) dry spots under gel coat
     

    Attached Files:

  2. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    The voids under the rail is called alligatoring, caused by the laminating resin attacking the gelcoat. There are various causes, usually too thin of gelcoat or the gelcoat not cured enough before laminating.
     
  3. bedfordd
    Joined: Apr 2013
    Posts: 10
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    Location: San Diego

    bedfordd DonnieB

    Yeah, good call. It could have been pretty thin at the rail as my mold is the same color as the gelcoat for this boat... Thanks!
     
  4. bedfordd
    Joined: Apr 2013
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    Location: San Diego

    bedfordd DonnieB

    Also, I'm now inclined to hand lay-up the glass to the gel coat then load the boat with the rest of the material and then infuse it. Any thoughts if this is crazy or not? Thanks...
     
  5. SamSam
    Joined: Feb 2005
    Posts: 3,900
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    Location: Coastal Georgia

    SamSam Senior Member


    You might have 2 different problems, improper gelcoat application/cure being one and the resin distribution system for the infusing being another.

    As far as hand laying a skin coat, there's nothing unusual about that but if the laminate is ending up dry, it wouldn't seem to remedy that problem unless there are air leaks in the mold which the skin coat might seal up.

    Try 'searching' in the fiberglass boat building section using various search words. Gelcoat problems are numerous and mysterious and have been discussed extensively. 'Infusion' should bring up a number of threads about the process and it's problems.

    Also, when you pull up a thread, scroll down to the bottom of the page for a list of 'similar threads'.
     
  6. SamSam
    Joined: Feb 2005
    Posts: 3,900
    Likes: 198, Points: 63, Legacy Rep: 971
    Location: Coastal Georgia

    SamSam Senior Member


    You might have 2 different problems, improper gelcoat application/cure being one and the resin distribution system for the infusing being another.

    As far as hand laying a skin coat, there's nothing unusual about that but if the laminate is ending up dry, it wouldn't seem to remedy that problem unless there are air leaks in the mold which the skin coat might seal up.

    In the fiberglass boat building section, try the 'search this forum' function using various search words. Gelcoat problems are numerous and mysterious and have been discussed extensively. 'Infusion' should bring up a number of threads about the process and it's problems.

    Also, when you pull up a thread, scroll down to the bottom of the page for a list of 'similar threads'.
     

  7. bedfordd
    Joined: Apr 2013
    Posts: 10
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: San Diego

    bedfordd DonnieB

    Thanks SamSam, I'll give search a try...
     
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