my own transom thread

Discussion in 'Fiberglass and Composite Boat Building' started by gtflash, Jul 28, 2014.

  1. gtflash
    Joined: Jun 2006
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    gtflash Senior Member

    Thought id update my own thread.

    Finally got all the ply off, and down to the solid glass in most areas, having trouble getting some of the bonding paste off of outside skin of glass. I found this wasnt reliably solid, so have drilled exploritory holes till i reached the fibreglass skin, where i couldnt get it off. I presume it was applied with a toothed tool.

    Cut the ply ready to go in also. I have tappered the edges to save some filler. It is 3x3/4" Except the top edge which is only 2x3/4 for the outboard well thickness. There is about twice as much ply now.

    Questions pleae. I need opinions.

    Is it ok to bond to the original bonding paste?
    How many layers of tabbing to hull and stringers? I am using 450g bi-axial and west epoxy?
    How many layers of glass on inside face? This is an ex race boat. weight is still on my mind, 275hp outboard. Ran about 75mph before.

    Next I will bond ply together, smooth off the sharp edges, bond it in place with microfibres and cabosil, (temporary fixings of ply made to screw from outside), I will use foam to transition from bottom centre to solid lower transom, so bond that in place, then glass the hell out of it.
     

    Attached Files:

  2. gtflash
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    gtflash Senior Member

    good day yesterday. No pics yet as its covered in peel ply.

    Managed to get

    4 layers 450g bi-axial of tabbing onto transom

    4 layers of 450g bi axial over the ply, 2 in alterate direction.

    thick goo mix over transom knees, followed by 8 layers of 450g over the knee to nbuild thickness, 4 of these tab to the remainder of the existing knee which were almost 10mm thick.

    I wanted to isolate the knees from the ply core, they are closed cell foam, but i wanted to eliminate any leaching, I also didnt want the knees to be an add on to the transom, so I laminated the knee to the sold outside backface of the transom, then covered a layer of the ply's fibreglass, then 2 of the knees, then one layer on transom again and so on. I hope thats ok, it makes sense in my mind.
     
  3. gtflash
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    gtflash Senior Member

    update

    I added another 3 layers to side of knees, and one more ontop pf 450g biaxial
    another 2 layers to centre section of transom and one more corner tabbing on outside, that links to outside solid hull element.

    I put 3 topcoats on today. I never used pigmemt in epoxy, I found it really difficult. I used 5% west system white, and 2% 422, barrier coat, to make a light grey. It didnt flow into the pinholes as I would have liked, so now I dont know if I should sand it back and topcoat again, or paint?? Any opinions welcomed please

    I attached a holesaw, cutout. This is the solid laminate element of the transom. The added thickness is cleary visible ontop of the original solid glass
     

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  4. KnottyBuoyz
    Joined: Jul 2006
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    KnottyBuoyz Provocateur & Raconteur

    Looks like it'll be good 'n solid! The extra effort will be worth it.

    For pinholes I have a little abrasive wheel thingy on my dremel tool that I used to hollow them out. Just fill them with a little thickened epoxy.

    That epoxy pigment is nasty stuff! I'm just going to paint over mine.
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I use pigmented epoxy fairly regularly. Mix the resin with the pigment first, then add the hardener. It also helps to thin the pigment with denatured alcohol first, then add this to the resin. This of course is for liquid pigment, which admittedly is a pain in the butt. I use dry pigments, which can be added after mixing the resin/hardener. I use acrylic paint pigment powder.
     
  6. gtflash
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    gtflash Senior Member


    Hope so. The knees are not uniform in shape, which bothers me a bit. But I wanted to keep as much of the original laminate there. Seemed such a shame to grind off a massive lump of solid fibreglass that was already tied to the outer solid face. Its got an extra sheet of 3/4" ply too.

    The boat was originally rigged with twin 150 outboards, then swapped to single 250. The ply face is straight, to give me an extra inch in engine height and a straight face for new outboard well rear seat. The transom was originally cut at an angle. Bigger prop and a bit more speed with luck too. :D I have added thickened epoxy to the otherside, which isnt finished yet.
     
    Last edited: Aug 10, 2014
  7. gtflash
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    gtflash Senior Member

    Thanks Par. Not many local sources for the dry pigment, I might try an art shop. Hurricane Bertha is apparently bringing us in the UK 12 hours of rain today, so I am going to get dressed up and do a little wet sanding, then let nature wash it away.

    I have a load of polyester pigment, can I add that to west epoxy, and thin it slightly too? I found it really difficult filling the weave, and dont really want to add excess filler as the area will eventually be unseen. When the epoxy is newly mixed it works for a few minutes, then as it starts to kick the roller falls appart and the epoxy seems to only go ontop of the high spots and not in the lows. With a brush it takes a lifetime. :mad: I use a big flat tray to keep the mixed resin in too.
     
  8. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Most artist or paint supply stores have dry pigments.

    Use a squeegee, putty knife or plastic bog applicator to apply thickened weave filling coats. I apply more then enough filler to insure the weave is filled, knowing I'll sand the bulk away, fairing and smoothing later. It saves the bother of multiple coats, just to fill the weave. In out of the way places, I try to be neat about this, so my efforts later are minimized.

    If you're only getting a few minutes of working time, you need a slower hardener. I'm the slow hardener king, having my own proprietary super slow that's still working nearly an hour after mixing in 90+ degree days. If using West, switch to their 209 hardener, which is pretty slow stuff. If using the slowest available with your brand, try working at night, so temperatures will be lower.
     
  9. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    I tend to use Gelcoat pigments to colour epoxy. However I have not tested ultimate strength with them, but use them for surface colour and some semi structural glass layups, decorative trims for edge beading.

    Note these are the pigments for gelcoat NOT gelcoat itself. There are some epoxy gelcoats around too. However with the polyester gelcoat pigments, I mix the colour and shade prior to adding to the epoxy. So far this has worked well as a finish coat over epoxy, epoxy/glass and the aforementioned trim strips have remained in place with no sign of delamination. As some of these are almost 20 years old it cannot be too bad. I use the minimum ammount probably around 2% pigment into the epoxy to get enough density of colour but trying not too damage any internal chemical bond in the epoxy. If you are using as part of a structural part, I'd recommend testing some test pieces first to make sure. For surface coating it seems to be OK, but be careful to get a good flow to the coat and pop any small bubbles with gentle blowing from hair dryer/heat gun.

    With some polyester repairs I also mix some of the pigment into the resin on the layer just under the gelcoat to help achieve colour depth. Some gelcoats, especially white if they are very thin, say sub 0.5mm become a little translucent so this helps retain colour depth in the final gel.
     

  10. gtflash
    Joined: Jun 2006
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    Location: uk

    gtflash Senior Member

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