Why gell coat?

Discussion in 'Fiberglass and Composite Boat Building' started by Nick F, Apr 23, 2009.

  1. Nick F
    Joined: Aug 2008
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    Nick F Junior Member

    A question for all production boat builders.

    Why do all small production Trailer boats use gellcoat finish?
    Is gellcoat more UV stable than paint finishes?
    Is gell coat harder then a Hardened paint finish?
    Which would last longer? Good automotive grade paint system or gell coat?

    I under stand that this is primarily a cost issue as the part has its finished surface straight out of the mold.
    I know allot of the top range aluminum boats are now being painted.
    but surly the boats that are being marketed as premium boats in there class could do better than standard gell coat finish.
    You wouldn’t see a Ferrari in a Gell coat finish would you.

    Just interested in people thoughts

  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    It gives a superior looking finish to 'just paint' as well as exhibiting better protection against water ingress into the laminate.

    Aluminium does not need to be painted, assuming it is marine grade alloy.
  3. jim lee
    Joined: Feb 2007
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    jim lee Senior Member

    You need some sort of coating on the mold for ensuring a release. Also, gelcoat can be patched up way easier than paint. Many boo boos can be "buffed right out".

    -jim lee
  4. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    "exhibiting better protection against water ingress into the laminate"

    I don't necessarily agree with that one, however, it is simply the cheapest and easiest finish to have when making a grp boat in a mould.

    Certainly there are other products that are far better at waterproofing and also finish quality, but production boats are almost universally produced at a cost first basis, quality is often compromised to achieve a saleable item, but not so far that it is either detrimental to the end user or unsatisfactory finish that the product will not sell.

    Polyester gelcoats are very cheap product, everywhere in the world there is no cheaper alternative that can produce the finish obtained if done correctly from a quality surface finished mould....all boild down to money...the reason we work.
  5. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect


    I don't design with composites too much, simply because the material choice is generally dictated by the designs SOR. However from memory and bits I've picked up along the way, as well as some data sheets I have, all organic paint coatings are capable of transmitting small quantities of moisture, at the molecular level; owing to gaps or holes which exist in the molecular frame work.

    Whereas density cross linked coatings like epoxies and two pack polyurethanes exhibit the lowest moisture permeabilities, 'loosely linked' polymers, such as those used in conventional alkyd paints are very much more permeable, and hence provide a minimal moisture barrier.

    It is about a 4:1 ratio in permeability on the charts I have.

    But you're right, all ''design' issues boil down to money...
  6. ABoatGuy
    Joined: Aug 2004
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    ABoatGuy Member

    Agree with AdHoc et.al., gelcoat is simply a cost effective solution for a decent finish.

  7. stilloutoffocus
    Joined: Apr 2009
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    stilloutoffocus dealership repair flunkie

    as ive seen (being a sea ray certified composite repair man, for all thats worth) gel coat seems to go on thicker and last longer (especially on the keel where we see alot of "beach rash") and as most production boat companies use polyester or vinylester resin the polyester based gelcoat gives a better bond to the laminate. however i am told that the modern epoxy paints, imron, deltron, etc. are just about as hard and adhear to the laminate just as well. i was actually taught that poly bonds to poly vinyl bonds to poly and epoxy and epoxy bonds to everything. but what it really boils down to from a repair standpoint is how well the repair person works with the given material. i find my gel repairs much easier and better looking than my paint, but the guy i work with does a much better job with imron than gel.
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