Redoing a 79 mako, epoxy or ester

Discussion in 'Boatbuilding' started by Hojo, Jul 16, 2022.

  1. Hojo
    Joined: Jun 2022
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    Location: Olean

    Hojo Junior Member

    Hi. Redoing a 79 19' mako. Had to go from outside on transom. Down to bare fiberglass and looking for your advice. I am on classic mako also but get dualing advice between epoxy and ester. I have 4 18mm sheets of hydrotek for transom and new stringers. 3 12 mm hydrotek for new deck. I bought 1 roll each of 1708 biaxial and 1.5 oz csm and have 5 gallons of polyester and 1 gallon of epoxy and 3 gallons of cabosil to start. I am new here and at fiberglass work. If you could help me I would appreciate it. I have read alot and see your experience in the field. I have some bolt holes and a few bigger holes. These appear to be caused by bolts and washers coming through possibly by an accident.
    With the above materials what would your recommended replacement process be? If you want to message me I have few more...lol.. Thank you.
     

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  2. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    You messed up the cut to remove the old wood, it should have a much wider surface to bond to. Epoxy is your only good option.

    The CSM is of little value with epoxy.

    The Biax will work, but the CSM component will suck up a great deal of epoxy, which will add weight and cost, with little added strength to show for it. Better to use 1700, it has no CSM attached.
     
  3. Hojo
    Joined: Jun 2022
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    Hojo Junior Member

    I had to go to that point to due to damage from previous owner. Ok. Will order that. Would you put a layer or 2 of 1700 first then 2 layers of 18mm of plywood then skin? Or just peanut butter and then right to hydrotek. Of course I will seal it with epoxy and sand before applying to boat. Thank you.
     
  4. ondarvr
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    ondarvr Senior Member

    It depends on how thick the skin is on the inside of the transom, and how much room you will have between the two skins.

    When that much of the transom has been removed from the outside, the inside skin becomes more important.

    If there is access from inside the boat to allow adding more glass to inside skin, I'd do that, the ply would only need to be bonded in place if that's the case. Then glue the ply together and glass it from the outside.

    If that's not possible, I might put a layer or two of glass on the inside skin and wrap it around to create a larger flange on the outside. Any flat piece of something could be used as a mold surface to make the flange an inch or two wider. This will add a great deal of strength and lock the outside skin in place.

    The ply thickness would be whatever it takes to fill the space between the two skins.
     
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  5. Hojo
    Joined: Jun 2022
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    Location: Olean

    Hojo Junior Member

    The remaining inside skin is about 1/2" at top but gets thinner at bottom where the larger bolt holes are. The original transom height was 20". Raising it to 25". My plan was to sand gelcoat on inside and add glass from back and over the 5" new plywood and onto inside skin. Would epoxy a piece of the 12mm hydrotek on inside 5" rise before glassing. Would utilize the entire existing transom as much as possible. Did not plan on removing fish boxes. So all that area would still be strong. Was just going to cut out deck around that area and replace. Not sure if this information will make any difference in your recommendations or not. I ordered some 1700 to do this. Thank you again for your help, advice and experience.
     

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  6. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Are you planning to use an outboard with 25” shaft? That’ll be getting the weight up pretty high for just a 19’ boat.
    A 20” transom should be safe, unless you’re planning to go really overboard with the power.
    BTW, those boats get real squirly at high speeds!
     
  7. Hojo
    Joined: Jun 2022
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    Location: Olean

    Hojo Junior Member

    Hey kapnd,
    I have a 125 mariner outboard....ran this boat for 2 years and top speed was like 38mph with just 2 of us and gear. This boat sits very low in the water and is very heavy. Had a few waves break over while slow trolling. And scupper hole was below the water. Trying to avoid same scenario. Thanks for input and always welcome any and all.
     
  8. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Glad someone other than me said epoxy after you cut that massive hole.

    The problem is the external glass has nowhere to land on the existing boat, and you can't land it all on top of itself in good construction, but now have no choice.

    I have no idea how you are going to glass the outside. There is not really a practical way to develop bond strength from the hull to the hydrotek other than epoxy. You would neat coat a prefabbed hydrotek panel with epoxy and let it kick or about an hour and then make a peanut butter epoxy putty with fumed silica. Coat both the boat and the hydrotek with the pb using an 1:8" trowel on the boat and then 1:16" trowel on the ply. Then you have to have bolt holes and tighten the panel to the boat with waxed bolts. Then the next day pop the bolts out; redrill and add another piece. An amateur has no business attempting to do the entire repair in one day because it'll be too easy to mess it up. And, most likely too many layers of wood are planned as epoxy requires glue space.

    All the ply required precoating or the resins can get sucked away from the fuller and you get a dry joint.

    The spacing of the finished joint is about 1mm which is 1/16" vee trowel each side and pressure. The first joint against the old boat, I'd go bigger.

    Honestly, I hate the repair you are doing because you are expecting the old polyester bond to support the new transom and I have no way of knowing the quality and don't even like to support the repair cuz I don't want you on the bottom of the river when the transom falls off.

    If you do this repqir, I recommend installing enough flotation foam so the boat can't sink if the transom fails.

    I probably stay woth the 1708. Two yards per layer is about 1/2 gallon or 50 oz of epoxy per layer at 1:1 or about 3-4 gallons.
     
  9. Hojo
    Joined: Jun 2022
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    Location: Olean

    Hojo Junior Member

    Ondarvr, when you see this could either send private conversation or e mail me at firemanhoj@yahoo.com? I tried to initiate a conversation but I can't for some reason. Thank you.. Howard.
     
  10. fallguy
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    fallguy Senior Member

    Make sure when you glass the exterior skin that you wrap each layer up and over a well radiused top. This is some good insurance against a failure. You would be able to dart or cut the overlaps to allow for contour differences, but you ought to go all the way into the splashwell on old glass and not gelcoat. This would also require bedding the first layer of glass in epoxy putty to deal with grinding variations or prepairing the grinding work to flat and making sure to have a 40-60 grit surface for glasswork.
     
  11. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    After you get the first piece of plywood attached or all the plywood done for reinforcement, grind all the gelcoat off here and up the inside edges and epoxy glass to the old glass.

    C3E06A5E-820A-4CAD-AECB-978442290D22.jpeg
     
  12. Hojo
    Joined: Jun 2022
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    Location: Olean

    Hojo Junior Member

    Fallguy,
    That was my thought. I think I will cut out the deck also and go 6" further down in that area. May be over kill but with the situation can't hurt. I am also raising the deck 1 to 1.5 inches to help with water. Thought there then would be to tab new deck to that area also to add more strength.
    Then after adding 2nd piece of plywood doing same concept in the areas to left and right where the cleats are in picture..grind to bare fiberglass.. ect...I think that will give me best outcome. And yes I will do one step at time. Thanks....
     
  13. Hojo
    Joined: Jun 2022
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    Location: Olean

    Hojo Junior Member

    This project is a total transom, deck n stringer rebuild....repaint....or BONFIRE!!!.....LOL
     
  14. Hojo
    Joined: Jun 2022
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    Location: Olean

    Hojo Junior Member

    Moving along, I have ground gelcoat off inside splashwell in preparation for this repair. Will grind off more around inside by fish boxes and top so can wrap glass in those areas also. Question now is when making the peanut butter to bed glass and ply to existing skin would I add 1/4 or 1/2 chopped glass fibres with cabosil or just cabosil alone?
     

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  15. Hojo
    Joined: Jun 2022
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    Location: Olean

    Hojo Junior Member

    Last picture was kinda dark...I am referring to grinding gelcoat down to glass in area along fish boxes and all inside the rear transom up to where cleats are in picture. And when I bring glass over from back it will attach to this area too. Blue circled area. Thanks.
     

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