Fiberglass repair on a rowboat

Discussion in 'Boat Design' started by kerosene, Jun 4, 2022.

  1. kerosene
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    kerosene Senior Member

    I have a typical (here) 80s fiberglass rowboat. The rear seat/floatation tank has leaked for past few years. Probably water plus winter has caused cracks - few decades of this.

    I am planning on sanding the areas open (from outside) the look like there is damage. My current plan is to add woven cloth and use polyester resin. Then pain gelgoat on top. Does this sound about right.

    also planning on adding an 8” access hatch to the tank to allow for better venting in the future.

    does this sound reasonable?

    doesn’t need to be pretty. Also picture is similar, not my boat. Will post pictures when I get the boat to our yeard.
     

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  2. fallguy
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    fallguy Senior Member

    Sounds okay, but sanding the gelcoat down and exposing the crack and feathering it down will weaken the area.

    Since you are planning an access hatch anyway; perhaps coordinate the access hole and the repair and do the patch on the inside mostly. Then you can finish it without a hump.
     
  3. ondarvr
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    ondarvr Senior Member

    And don't use only cloth with polyester resin, it will fail. Mat needs to be used.
     
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  4. wet feet
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    wet feet Senior Member

    I agree with the advice to use mat.Are you certain the tank doesn't contain foam?Some builders have foamed their tanks as a matter of course and if yours is one,it will be a bit of a challenge to clean enough out to carry out any work.
     
  5. kerosene
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    kerosene Senior Member

    IMG_20220604_162653.jpg tank has no foam, I don't see any visible cracks on tank areas now that I have it at home.

    There is one crack near keel that needs fixing and many small nicks on gel coat.

    The seat support parts are soft inside (wood) so I think I have to open and empty them and make a new top surface.

    The no cloth was news to me. what is the reasoning for that?

    also, not hugely worried about subtle humps on the outside. Not a race boat.

    IMG_20220604_154053.jpg IMG_20220604_161026.jpg IMG_20220604_161915.jpg IMG_20220604_162643.jpg IMG_20220604_162409.jpg
     
  6. wet feet
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    wet feet Senior Member

    The boat is in fair condition for it's age and won't take a huge amount of fixing.My guess is that those cracks have been caused by impact of some kind and I would make an effort to open them out just enough to get to a clean surface and then fill with fresh gel.Something like a Dremel and a very shallow groove would be good.It isn't really that hard to carry out a gel repair and your biggest challenge might be getting a close colour match,if that matters.Once the cracks are filled it will be a barrier to water entering the laminate and it might be sensible to add a patch of mat to the interior over the damage zone.Mat is preferable to cloth because it will conform a little more readily and doesn't have the potential leak paths through the weave.Cloth has better tensile strength in the direction of the fibres and in more demanding applications it is common to cut the cloth to make certain that the fibres and load paths align.If the wooden thwart pads have lasted 30-40 years then they haven't done badly really and replacing like with like will probably work,a couple of plies of mat extending outwards by 60-70mm all round the pads will probably suffice.The helpful images of the boat don't really allow any realistic chance of guessing whether the hull might have been laid up with a chopper gun.Lots were,for speed of production,and the quantity of glass may not be as uniform as one might hope.Which might account for the odd crack.With a few hours of work you should have a boat able to function for many more years.Good luck.
     
  7. fallguy
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    fallguy Senior Member

    Mat makes the glass thicker and less likely to leak.

    If you only have stitched glass, use epoxy.
     
  8. kerosene
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    kerosene Senior Member

    Thanks for replies.

    I am tempted to use glass cloth as I have it at hand already - and it is nicer to handle. But if it really is an issu with the water traveling withing the weave I'll reconsider.
    Stuff like gel coat color matching doesn't matter the least bit. Getting on the water before summer is over matters .

    And as I sand the crack open, and the seat block attachment, is an 80 grit surface good for getting a solid bond?
     
  9. ondarvr
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    ondarvr Senior Member

    The issue with using only cloth is the ability of it to create a good bond to the existing fiberglass surface.

    When cloth is right up against a surface you end up with a resin rich zone between the two, this resin rich zone is weaker than the areas with glass. As a result, when stressed, the resin rich zone fails first and the cloth peels off rather easily. Because of the random short fibers in mat, it will more closely follow the existing surface, that resin rich zone now has significantly more glass in it, which increases the strength.

    Though, in reality the actual resin bond is the same, the difference is that the higher glass content at the bond line reduces the chance of it failing.

    This is one of the reasons people perceive that polyesters bond so poorly to things. The bond may be good, but that resin rich layer is comparatively weak. Epoxy is a much stronger resin, so it doesn't tend to fail in the same way when used with cloth.

    Leaking is from the cloth being so thin it may not hold enough resin to form a uniform barrier for water. The gaps between the weave may not be completely filled with resin, they can be difficult to see because they are so small.
     
    Last edited: Jun 5, 2022
  10. kerosene
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    kerosene Senior Member

    opted to go with epoxy and cloth.
    I already have some supplies and "enjoy" working with epoxy over polyester anyway and the amounts of resin needed are very small so no budget issues.

    Roughing up the the surface for epoxy - 80 grit?

    bought supplies yesterday - also for painting it inside and out - epoxy primer, will get polyurethane top coat later.
    Tried washing coloring and gunk and a biodegradable acidic (oxalic acid) rim cleaner. Seems to work pretty good.

    General plan also changed slightly - I will make a new closed seat that can store a battery for a trolling motor. Also will make fiberglass cable channels from that mid seat to fwd and aft seats. Pics to follow when I get something done.
     
  11. kerosene
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    kerosene Senior Member

    1st day
    cut out the blocks for seat attachment and oar locks. Amazingly they were not soft even though waterlogged.

    Now I have quite deep recessed areas from where those were cut - was going to fill with glass tape and epoxy-silica mix to level with the surface around these and the put layer or two of glass (300g) that extends a few inches over the seam.

    The recessed areas are fairly deep - about 1/4" / 6mm. Is filling it with laminate stupid and waste of time? any hints in smarter ways to fill them.

    About the damage / cracks, I think it is damage from being stuck in ice.





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  12. kerosene
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    kerosene Senior Member

    some work put to this.

    most cutting and opening done.

    everything seems pretty straightforward except it seems the keel is water logged in the rear. I did some test drilling and up to about 3rd way from rear the shavings were wet. I suppose there is a wooden core for the keel. the drilled out "shavings" were bit hard to identify to be honest.

    I really don't want to cut it open. Will "close it up" from the inside of the boat but will revisit the issues once I flip the boat over.
    IMG_20220620_145323.jpg
    IMG_20220620_145310.jpg IMG_20220620_145328.jpg
     
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  13. mc_rash
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    mc_rash Junior Member

    The cut out areas for the oar locks might be weak points and could crack if not well done due toe bending of the hull. But I guess your procedure with one or two layers glass extending a few centimeters (6-7 cm as Wet Feet said) will be sufficient. Make sure there are no sharp edges so the glass can be laid without air beneath it.

    For the keel I would go the following way if it's my boat. Make sure it is really wood and it's wet otherwise you can skip to the last steps. Drill some holes (~10 mm) with some distance along the sides of the keel. Let it dry for a few weeks. Fill the holes with thickened epoxy and repair the cause for why the keel is getting wet. Done.
    Maybe there are better, faster methods than mine, you want to enjoy the summer on and not under the boat.

    Btw, I appreciate that you give dimensions in imperial AND metric units!
     
  14. fallguy
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    fallguy Senior Member

    You can dry the keel with halogen heat lamps of you put a few holes in it, but the risk of fire is high. Within about 60 seconds of the water boiling out, the temperature will go from 212 to like 400 and catch fire or burn the finishes and catch fire. So, you can do it, but do NOT walk away from monitoring the steam release.
     
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  15. kerosene
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    kerosene Senior Member

    have made some progress with gassing over the cracks but expanded the project into a custom seat, which hasn't progressed that much.

    seat will have, under a swiveling lid, battery compartment, cooler and a 3rd box for maps and misc. junk.

    today made a quick cable channel from future mid-seat to rear.
    XPS taped down with packing tape. And then glassed over. Not very elegant but hopefully will work out OK.

    the channel will be trimmed, down tape and foam removed etc. and then glassed on place.
    is 3x 300g (9oz I think) cloth final thickness going to be reasonably strong for occasional stepping on it etc.?


    IMG_20220628_155204.jpg IMG_20220628_155217.jpg IMG_20220628_155238.jpg IMG_20220628_155256.jpg
     
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