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Permalink Reply by Bennett Yarbrough on October 21, 2016 at 11:17am

Been giving this some thought.  If I were to durabak the interior bottom then glassed the exterior bottom there would be no way for moisture to escape the ply if it were say gouged on a river trip?  However, with oil its no big deal because moisture can wick out literally across the entire top side?  Do I have this right?

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Permalink Reply by Randy Dersham on October 28, 2016 at 1:05pm

Plywood is sealed layer by layer with the glue that is used during manufacturing.  The moisture escaping that you describe can happen with solid lumber but not with plywood or any laminated wood. It can only dry on the most outside layer or via the gouge hole or where a screw has penetrated. 

That is the dark side of plywood or any cold mold method.  Water cannot escape through the layer of waterproof glue.  Any gouge or screw that goes through plywood will allow water to enter in the interior layers with no way to escape except the small space where it entered.  Unless fully encapsulated and protected from any water, screws will eventually fail in plywood.  The amount of time that takes for that failure to happen is lengthened if the boat is allowed to completely dry in the off season (garaged boats, preferably with reasonable heat) It is shortened if the boat is constantly wet. Oil can help some by displacing water but is the least efficient.

Fully encapsulated screws (durabak, glass and epoxy etc) that do not allow any incursion of water will last the longest; however, it is not unusual for the expansion and contraction differences between the metal and the wood to create micro cracks that allow water to seep around the screw.

I use durabak but I also like oiled boats.  I personally don't use oil on the boat bottom because it collects dirt. It is my opinion that a oiled boat interior bottom is more beautiful and classic but they are harder to clean.

 

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Permalink Reply by Bennett Yarbrough on October 30, 2016 at 10:38am

Thanks for i he insight randy. I'm thinking durabak makes the most sense for me

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Permalink Reply by David Cline on December 26, 2016 at 10:53am

I'm about to start my first build, and pull the trigger on my materials list.  I'm building a 12' OAL McKenzie with transom that will be used for fishing and floating on mellow rivers.  I love wood visually, and so I'm not inclined to paint it, and I hate the way varnish chips and peels.  For that reason, and simplicity sake, I'm considering a fully oiled finish, inside and out, rather than glassing anything.  The boat will be garaged when not in use, and will live in a dry climate (Denver).  Am I crazy?  

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Permalink Reply by Bennett Yarbrough on December 26, 2016 at 3:47pm

I started gluing my frames today and have decided that durabak vs oil will be settled once my hull is built. I'll just throw a layer of epoxy down if I decide to durabak

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