Ply outboard bracket...epoxy or not?

[Greenheart]

I can hardly believe I'm asking because leaving an inch and a half of end-grain unprotected sounds beyond daft. But under the intense pressure of clamping and unclamping the engine, plus all the vibration involved in running it, isn't it likely that the plywood will deform somewhat inside its epoxy skin, and shed it like a crisp crust?

In the past I've noticed epoxy rising off plywood that had encountered flexing, so I suppose I'm asking if there's a special epoxy mix or type (or some quite different treatment) that can flex a bit.

My Avon's outboard bracket isn't ply at all, but I had the ply already and it didn't occur to me to use hardwood till now, at rather a late stage. And lots of outboard brackets are made from ply, so I guess it must be okay. Just not sure about the best waterproofing.

 

[RJJ]

I can hardly believe I'm asking because leaving an inch and a half of end-grain unprotected sounds beyond daft. But under the intense pressure of clamping and unclamping the engine, plus all the vibration involved in running it, isn't it likely that the plywood will deform somewhat inside its epoxy skin, and shed it like a crisp crust?

In the past I've noticed epoxy rising off plywood that had encountered flexing, so I suppose I'm asking if there's a special epoxy mix or type (or some quite different treatment) that can flex a bit.

My Avon's outboard bracket isn't ply at all, but I had the ply already and it didn't occur to me till now, at rather a late stage. And lots of outboard brackets are made from ply, so I guess it must be okay. Just not sure about the best waterproofing.

Maybe wrap it in mat a few layers thick first to limit the flexing?

 

[Greenheart]

Hmm, thanks, most likely I will.

I think I was afraid that applying a thick layer over the ply would reduce the natural grip that the clamps can exert on the wood.

Thinking harder about it, there's no way a 3.5hp engine is going to make 34mm of plywood flex. Actually it's 25mm plus 9mm.

I remember how the ply bracket on my other boat got chewed up by the clamps of the Mariner 5hp. Would it help to plate the bracket with thin sheets of stainless, or are the clamps likely to slip on something with no 'give'?

I suppose I need one of those rubbery pads that fit over the top.

 

[Bajansailor]

I think I would have a nice radiused curve on that 34 mm thick of end grain, and wrap a layer of tight weave cloth (not mat) set in epoxy around it.

 

[waynes world]

Just stick some ally where the clamps rest. 3mm will do the job. if the clamps are good thenm they will not come loose and they can be locked inplace usually they have holes in the tightening tabs to fit a padlock etc, if not drill one in each one.

KESOTO Handle Transom Clamp Screw Bolt Assy Replacement Part - Fit for Yamaha Outboards 6G1-43116 6E0-43118-00 : Amazon.co.uk: Automotive

 

[Neeves]

I'd say you are wasting your time.

Eventually - 2 weeks, 2 months, 6 months the ply/glass/epoxy will degrade, It will fail, depends how you define fail.

Accept reality

Make 2 or three and discard with time. Its not going to cost you a fortune to make three bits of ply, or hardwood - ..... treat them as sacrficial

Just do it!

Jonathan

 

[burgundyben]

Too late to say this but a solid lump of composite built up would not need epoxying.

 

[Laysula]

I bought one of these 5 years ago. Just bolted it on and left it. Still fine. It's just not worth the hassle of fannying about with epoxys and varnishes etc.

Hardwood Outboard Mount - K J Howells & Son

 

[ghostlymoron]

I'd say you are wasting your time.

Eventually - 2 weeks, 2 months, 6 months the ply/glass/epoxy will degrade, It will fail, depends how you define fail.

Accept reality

Make 2 or three and discard with time. Its not going to cost you a fortune to make three bits of ply, or hardwood - ..... treat them as sacrficial

Just do it!

Jonathan

That was what I was going to suggest. I wouldn't bother with epoxy as it soon degrades with sunlight and you don't really need a high gloss finish. I'd use a stain/preservative and slap another coat on annually.

 

[chriss999]

I didn’t bother epoxying or glassing mine and it lasted years. And still looks reasonable. In my case the plywood was free and I’ve got more for when I need to make another.
If I’d had more time I might have glassed it but as I had plenty of other boatie refurb jobs I didn’t spend too long on this one.

 

[Greenheart]

Thanks gents, I reckon I'll try to include all those thoughts, especially not worrying too much...

...it's far from being my only job, too.

 

[Dellquay13]

Thanks gents, I reckon I'll try to include all those thoughts, especially not worrying too much...

...it's far from being my only job, too.

I used a nylon food chopping board, cut in half and doubled up in thickness

 

[johnalison]

I’d regard it as a disposable item, treat it with Patio Magic to stop it looking manky, and expect to change it every few years.

 

[Greenheart]

Chopping board's a good idea. I still have a couple in the garage which never yet saw cheese or carrots. I'd originally planned to add slabs of plastic either side of the ply, but feared it might be more slippy than wood.

 

[Bodach na mara]

The only problem with the solid laminate or layeres of poly chopping board is that if dropped in the oggin they sink. OK if you do it in shallow water but a pain if you're moored in Tobermory!

 

[Greenheart]

I weighed my (unfinished) bracket the other day...it's got so much steelwork bolted on, it's already over 2kg. So, not a lot of hope it would float, even without an engine attached. ?