adding glass-layer to existing underwater

Discussion in 'Fiberglass and Composite Boat Building' started by simon, Dec 22, 2009.

  1. simon
    Joined: May 2002
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    simon Senior Member

    I am thinking about glassing another layer over the existing underwater of my catamaran. The underwater will be glass blasted. Please see

    The existing laminate will be perfectly prepared for further treatment. I am thinking about adding another layer of glass.

    The hull is strip-planked, with one layer of 600grms biaxial. What is the best choice of reinforcement and strengthening abrasion-resistance of the hull and not adding a lot of weight? If possible, the new laminate should be pretty fair for further painting.

    Should I stick to biaxial and what weight?

    I was thinking of sticking all the glass to the hull with lightly applied 3M Super 77, which should not interfere with epoxy-curing. From there I have got the choice of wetting out the glass with epoxy and adding peel-ply. Vacuum bagging would be an add-on.

    If the glass is stuck to the hull, this could be starting point to infuse the laminate. Is this a reasonable option? Does it have to be done in one shot, or could the hull be suddivided and infused in several goes(sections)?
    The Hull is 13.5m long and has a short keel.

    Thanks for the feedbacks.

  2. apex1

    apex1 Guest

    What is the goal of all your action?
    Why adding another layer Simon?

  3. catsketcher
    Joined: Mar 2006
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    Location: Australia

    catsketcher Senior Member

    600 Biaxial or double bias? - it is pretty important to sort out the difference. If Biaxial has been used that is pretty dumb. In strip plank the planking is assumed to take the fore and aft loads and many boats have db outside and uni inside. Do not use biaxial to stiffen the structure.

    I would in no way vacuum. Bagging a whole hull would be a nightmare - glassing upside down is bad enough and if you are good with a squeegee you can get a good job with that.

    I don't know the 3M stuff but would simply put 400 uni on the thing - going across ways. You only have to do one wrap at a time - about 1.1 metres and do not overlap the uni. Then if you have to go home you can stop and start again the next day. You should think uni and it will be much much easier than anything else anyway. Use good epoxy and go straight over the existing laminate - you may need to put a very thin screed of epoxy with glue powder in it to fill in the valleys in the existing laminate.

    DON'T Vac Bag! It is a pain in the bum.


  4. AndrewK
    Joined: Mar 2007
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    Location: Australia

    AndrewK Senior Member

    Simon, I would be only doing this if it was absolutely necessary.
    No matter what weight and kind of reinforcement you use and even if you do not overlap as in catsketchers UD suggestion you will at a minimum have to trowel or brush on runny bog to fill the weave and than sand. All this work upside down will be a pain in the neck, literally.
    Yes you could infuse or vacuum bag in sections but I would not bother with this either.
    I would get a friend to help and wet out the reinforcement on clear plastic and lift this in place and press on to the hull by hand and clean roller to get it to stick on. Then peel of the plastic and use a sgueegee or wet roller to smooth out. Then as it starts to gel I would roll or brush on a runny bogg to fill the weave.
    If you want best abrasion resistance at minimum weight then you could use a 200g plain weave kevlar, but this will cost you 5 times the cost of 400g glass.
  5. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    ... and will be a pain in the butt when you hit it with sanding.

    If you need to (I say: IF) then apply a runny bog on the hull, indeed to fill the dents, but also to make the layer of fabric stick to the hull.

    A messy and nasty job. No possibility to turn the hull over?

  6. simon
    Joined: May 2002
    Posts: 101
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    simon Senior Member

    Hello everyone,

    thanks for the feedback.

    Correction: 600grms of Double bias used on the outside and 400grms on the inside.

    Phil: Do I understand you right, that you would put two layers of uniglass at an angle to the centerline, so that is would end up like a double bias?

    Andrew: Kevlar has good abrasion resistance, but would reinforce the hull with it's poor compression strength? What about the hybrid fabrics?

    Herman: a pity, but almost impossible to turn the hulls upside-down.

    Thanks to all for the contributions. I appreciate the good input.


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