73 21' Starcraft holiday IO - Marine grade ply

Discussion in 'Materials' started by JJO, Mar 17, 2015.

  1. JJO
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    JJO Junior Member

    73 21' Starcraft holiday IO - New transom & deck

    Hello all,

    I have finally gotten around to getting the outdrive, and engine out of my boat.

    I have read many of the transom core replacement threads on here. I think I have a good handle on the process of preparing a new transom from marine grade ply. I am not so fluent with the goos. But I will research that more soon.

    One question I have is: Is it okay to buy Marine grade ply from big box stores such as Menards/Lowes ect . . .?

    Also if you can view the images I posted, You can see the current transom (assuming original) core is made up of 2... 3/4" plys. I have read on hear to achieve 1.5 inches it would be better to use 3...1/2" plys??

    Also from the photo you can see that where the transom bracket bolts up to the transom there is a small additional piece of ply 1/2" to achieve 2" of thickness in that area.

    The engine is a 165 HP GM inline 6. 250CU straight 6.

    I was thinking of enlarging the small piece of ply when constructing the new transom. Ideally I would just make the hole transom 2" thick...
    However, the way the transom attaches to the boat at the side walls (forgive me on boat lingo) will only allow the 1.5" thickness.

    Thoughts on these questions??
     

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  2. gonzo
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    gonzo Senior Member

    It will be OK. The original was built with BC exterior grade. Good luck with the project
     
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  3. JJO
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    JJO Junior Member

    Transom & Deck

    So, would the deck have been the BC exterior as well? I believe what I pulled up off the deck was 3/4".

    Any thoughts as to weather I should just replace the core with a new core of the same configuration? Do I assume that since the original was built with BC exterior, and the new would be built with stronger marine grade AB ply that I will be good to go with the same config? Or would it be best to enlarge the small piece of 1/2" ply regardless of what the original was?

    Also any thoughts on what individual thicknesses should be? i.e. the two sheets of 3/4", and one sheet of 1/2". Or 4 sheets of 1/2"?
     
  4. gonzo
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    gonzo Senior Member

    The original lasted forty years. You are not likely to still own the boat in 2055. It was a good design. If you coat the plywood with a good quality exterior paint, it will last more than the original.
     
  5. JJO
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    JJO Junior Member

    paint after I do all the epoxy work?
     
  6. gonzo
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    gonzo Senior Member

    Anywhere where it will be exposed to the sun, epoxy should be painted. It doesn't have UV resistance.
     
  7. JJO
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    JJO Junior Member

    Epoxy thickening

    I have read on here to use products like West 404, and west 406. for thickening epoxy. Also Bateau.com recommends use of wood floor for thickening for ply lamination.

    So, for laminating the ply wood for my project should I use 2:1 marine epoxy, and wood floor? To make an epoxy glue...

    Would I used the same wood floor for thickening for bonding fastener holes?

    Should I bond the core to the aluminum transom skin? If I should do this would it be best to use a west product to thicken... Like west 406?

    Are there similar products available from Bateau as a more cost effective options? Just under different trade names?

    Is there one thickener that I could buy to do all the thinks I have listed above?
     
  8. PAR
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    PAR Yacht Designer/Builder

    BC exterior and AA marine aren't the same APA standard, having significant differences, though the same veneer count. 40 years ago StarCraft would have used 1-95 marine (APA) or MDO (also 1-95 rated) and this stuff would have been 7-11 veneer stock, compared to the 5-7 veneer stuff seen today. Imported marine grades built to the BS 6566 or 1088 standard will have 11 veneers and a much higher construction quality, which makes it considerably stronger, for the same thickness, compared to the APA stuff.

    As to bonding and laminating, you should download the "User's Guides" from WestSystem.com and the "Epoxy Book" from SystemThree.com. These will nurse you through the various materials and techniques.

    Thickeners or more appropriately, fillers come in many varieties and are used for many reasons, so no one material is good for everything. Most mixtures will have at least a couple materials in it, one to control viscosity and another to bulk it up. Yes, Bateau.com and other places like EpoxyProducts.com have much more cost effective formulations of goo and filler materials, compared to West System and the other major brands. They're not rebadged" products, but different formulations of the same base ingredients.
     
  9. JJO
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    JJO Junior Member

    Thanks PAR.

    I appreciate the post on my thread PAR. I had hoped you would drop in and lend your knowledge, and experience. I really appreciate the specific direction to the users manuals you suggested.

    I have reviewed both. I think I have a plan of attack.

    For the ply wood I intend to visit Menards and check to see how many veneers there so called marine AB grade ply has. If it has more then 9 layers I am thinking I will go with that plywood for the core. Ill pick up 2 sheets of 3/4", and one sheet of 1/2". I have read other post by you where you have recommended the use of 3 layers of 1/2 vs. 2 layers of 3/4, but that was an outboard boat...

    I am thinking, also based on the Gonzo's advice that a core replacement construction consisting of like (as compared to the original) layers will be sufficient... Also I am thinking the ply I intend to use is going to be superior to the original material... Feel free to let me know if this thinking is incorrect.

    As for the goo.

    I have ordered the 1.5 gallon kit of Marine epoxy.

    I intend to purchase west 404, and 403 from a local distributor.

    I will coat faying surfaces of the ply with 2 coats of neat epoxy before Appling thickened epoxy as the adhesive coat. I will thicken the epoxy with a mix of 404, and 403 adhesive fillers. A similar mix would be used to bond the core to the aluminum transom skin.

    I will coat the whole core as an assembly at least 3 times with neat epoxy, paying special attention to the edges surfaces of the ply wood.

    On all through fastener holes... I will bond them with a thickened mix. I was thinking with just 404. add 403 if viscosity control is needed??

    All fastener holes that are not through holes I will drill a deeper then needed pilot hole, then fill the hole with neat epoxy before driving the fasten to it's seated position. I was also thinking of using a marine RTV for the fastener heads... should this be done after the epoxy cures?? or is this not needed at all??
     
  10. JJO
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    JJO Junior Member

    The old core

    Finally got the round to-it I needed to pull the old core...

    I was surprised it held together when I pulled it out... especially the lower starboard corner...

    I counted 6 Veneers in the original plys...

    Also there were several what appear to be stainless screws that went into the core from the inside that did not go all the way through...

    Would these screws have been original?

    Should I just add through fasteners here?
     

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  11. gonzo
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    gonzo Senior Member

    The screws that don't go through were to hold the two layers of plywood together while the fiberglass/resin in between cured. There is no need to remove them since they will be encapsulated anyway. Is that 6 veneers per 3/4" ply?
     

  12. JJO
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    JJO Junior Member

    reply

    Yes appeared to be 6 veneers per 3/4 inch ply...

    The screws went through the aluminum angle that is riveted to the hull also, that's the angle that the core seats into..

    Thanks for the reply.
     
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