Heron restoration - deep bog

Discussion in 'Wooden Boat Building and Restoration' started by WhiteDwarf, Jul 29, 2012.

  1. WhiteDwarf
    Joined: Jun 2011
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    WhiteDwarf White Dwarf

    I am rebuilding a (Jack Holt) plywood Heron dinghy. In stripping off the top coat, I found that the hull had been remodelled considerably. The bottom panel hed been filled to a depth of 8mm when it butted against the bow pad.

    I have cleaned out the old filler, dry firm material which will yield to a sharp tool. Now I need to replace it and reshape the section shown in the accompanying photo.
     

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  2. rwatson
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    rwatson Senior Member

    Is there any fiberglass cloth on this boat ? I know it is supposed to be plywood, but that's a lot of filler where the plywood should be.

    If the plywood underneath is sound, then I would be inclined to mix up epoxy with lightweight microballoons and fill to about ~3mm to the surface. Then I would use some 6oz cloth, overlapping the other fair surfaces by around 300mm, and then fair the rest off with epoxy and perhaps a 50/50 cabosil/microballoon mixture to resist dings and knocks.

    Was this just a case of bad building to get this unfair, or has something else been going on ?
     
  3. WhiteDwarf
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    WhiteDwarf White Dwarf

    RW

    Thank you for your interest.

    No fibreglass on the boat and the wood is sound.

    I have been told that the boat placed 3rd in a Heron Nationals about 15 years ago, I understand she had a radical rebuild to test tolerances at that time.

    The shape is surprisingly complex, a definite hollow on the waterline, but all the restrictions of relatively un-tortured plywood in the lay of the bottom.

    To avoid the filler slumping, I was thinking of gluing formers made of 4mm ply along the line of the bilge and a couple more horizontally and two vertically, sanding them down to capture the shape; then filling the space between the formers with Q-Cell. Finally, covering the whole with 4 oz. cloth and doing a final fair.

    Is that over complicating the task?
     
  4. rwatson
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    rwatson Senior Member

    I think you have a good handle on the task ahead, and your plan is sound. Rather than ply formers though, I would be inclined to get some strips of good quality light wood, say WRC or similar . Depending on your purity gene, I would even seriously consider hi-density foam or even balsa, as the ultimate lightweight material.

    Not only would wood or foam be be lighter than ply, but if you had to do any fairing of the substrate, it would sand straighter and more evenly.

    I would suggest a minimum of 6 oz cloth on top, as the extra weight on that area would be so tiny, but laying up that really light cloth is a p.i.t.a and prone to extra work with epoxy, and you would get a bit better abrasion resistance and strength for your trouble.
     
  5. PAR
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    PAR Yacht Designer/Builder

    I'm not sure you need the formers. If the substrate is well toothed, the fairing mixture well bonded, you'll probably have the same success the previous owner had. Yep, it's a lot of bog, but I've seen much worse, last decades. Of course if you're a sailor that likes to bash into stuff, you might want to consider bulking up the area with strips of any light species. Plywood wouldn't be my first choices, because of weight. I also wouldn't use 'glass and again because of the weight and work, unless you're the previously mentioned type of sailor.
     
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  6. WhiteDwarf
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    WhiteDwarf White Dwarf

    Thank you Mr. Riccelli.

    In the general, no I prefer to avoid running into things. I am sure we can all think of exceptions, but...

    I planned to make the formers only 4 mm wide so don't see weight as an issue, their use merely a means of getting the shape before applying the bog. Frankly, I don't have the confidence to capture the shape freehand.
     
  7. rwatson
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    rwatson Senior Member

    You can ensure a good hull shape with 'reverse' battens. The idea is to get some flexible battens, cover at least the underside of them with plastic tape, and screw then to the outer edge of the hull, and have them pass over the 'void'. If you screw the battens at least twice on either side of the hole, they will form a fair shape based on the existing hull profile. You can be smart, and place these battens to cross at the more complex places.

    You can then apply the 'bog', up to and a bit over the battens, making sure you pack the bog firmly up against the bottom of the battens. When you remove the battens (courtesy of the plastic tape) you will have a series of grooves that will have followed the lines of the hull, that you can use as guides to fair the high bits to.
     
  8. WhiteDwarf
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    WhiteDwarf White Dwarf

    Job delayed but done

    Mr Watson, Mr Riccelli, thank you for your input, way back then. Its been a back burner job but has come up well - even if the photo rotates 90 degrees on upload...

    20140510 Zebec2bow.jpg
     
  9. PAR
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    PAR Yacht Designer/Builder

    Progress, way to go. Now, how about full up frontal nudity shots, of your freshly painted lass.
     
  10. rwatson
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    rwatson Senior Member

    Well done, you seem to work at the same pace as me, but the results look good. Shame to put it into the water and ruin the paintwork :)
     

  11. WhiteDwarf
    Joined: Jun 2011
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    WhiteDwarf White Dwarf

    Will this do PAR?

    C:\Users\RossVenner\Documents\Boats\Heron\20140515 Stbdbow.jpg

    Sorry for the 90 degree rotation again.

    Ross
     

    Attached Files:

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