Marine PLy or not?

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Tafflad

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I fitted a Tower to my boat this year, or in fact the dealer did.
I'm very pleased with it.

What I intend doing out of season is laminate in some supports behind the deck fittings, to cut down on flex, and strengthen the support point.

Intent is to glue in some 3mm ply - about 60cm x 20cm been advised, with fixing bolt through the middle. ... that is 1/8" of 24" x 8" for those not yet in 21st Century...

Once glue has set, glue in a second layer over the first.

Advised to use 3M 5200 as the adhesive.

The Q ... should I be using Marine ply for this, or as this is well above the water line, is WBP ply good enough.
I could always put a coat of yacht varnish over the ply & edges once fitted.
 
Welcome to the forum.

Dunno the answer, but if you post this on the PBO forum you should get an informed response.
 
sounds too big and too thin to me, better with smaller piece of thicker ply IMO. Also not sure what "laminate in" means, do you mean cover it with fibreglass? If not, then I think it's worth using marine ply for longevity. It may be better to use aluminium or stainless backing plates bedded on sikkaflex.
 
Tafflad said:
I fitted a Tower to my boat this year, or in fact the dealer did.
I'm very pleased with it.

What I intend doing out of season is laminate in some supports behind the deck fittings, to cut down on flex, and strengthen the support point.

Intent is to glue in some 3mm ply - about 60cm x 20cm been advised, with fixing bolt through the middle. ... that is 1/8" of 24" x 8" for those not yet in 21st Century...

Once glue has set, glue in a second layer over the first.

Advised to use 3M 5200 as the adhesive.

The Q ... should I be using Marine ply for this, or as this is well above the water line, is WBP ply good enough.
I could always put a coat of yacht varnish over the ply & edges once fitted.
Click to expand...

If you are using two thicknesses then it will be OK, I would use epoxy and epoxy the ply first to seal it and use WBP that will be plenty adequate.
 
I'm no expert, but marine ply is best for wet or moist environments. Your application may be above the waterline, but what about leaks, etc? If there is any chance of moisture then use marine ply for peace of mind.

Marine ply should also be free of defects and thus withstand maltreatment better.

Relying on varnish implies that you will maintain it.
 
ccscott49 said:
If you are using two thicknesses then it will be OK, I would use epoxy and epoxy the ply first to seal it and use WBP that will be plenty adequate.
Click to expand...

I was going to use 3M 5200 as Tower dealer uses that ... is there any type of expoxy that you are recommending ?
 
Nick_H said:
sounds too big and too thin to me, better with smaller piece of thicker ply IMO. Also not sure what "laminate in" means, do you mean cover it with fibreglass? If not, then I think it's worth using marine ply for longevity. It may be better to use aluminium or stainless backing plates bedded on sikkaflex.
Click to expand...

The dealer avised he uses 3mm ply as it will curve to shape of the deck better .. but I'm open to suggestions.
Is Sikkaflex better option than 3M 5200 ?
 
Tafflad said:
I fitted a Tower to my boat this year, or in fact the dealer did.
I'm very pleased with it.

What I intend doing out of season is laminate in some supports behind the deck fittings, to cut down on flex, and strengthen the support point.

Intent is to glue in some 3mm ply - about 60cm x 20cm been advised, with fixing bolt through the middle. ... that is 1/8" of 24" x 8" for those not yet in 21st Century...

Once glue has set, glue in a second layer over the first.

Advised to use 3M 5200 as the adhesive.

The Q ... should I be using Marine ply for this, or as this is well above the water line, is WBP ply good enough.
I could always put a coat of yacht varnish over the ply & edges once fitted.
Click to expand...

Need a bit more of an idea as to just what you are planning.

It sounds like you want to strengthen the area under the top of the gunwales to stiffen it.

The use of thin ply will allow you bend each layer to the shape of the underside and laminate (stick) more layers to build a curved beam.

Question one, will the layers of ply strips be glued to the underside or the outer hull?

If gluing under the gunwales it will not provide a lot of stiffness at only 6+ mm, consider at least 3 x 3mm layers.

Also note:
I would use construction ply, coated with an epoxy resin first, then sanded, then glued in with an epoxy resin and micro fibres mixed to a toothpaste thickness and propped into position making sure at least 1.5 mm of the mix remained between the ply and gunwale, so push it up too hard.

After all the ply is installed and the resin has cured, re drill the holes for any fittings at least 10 mm oversize and fill with the glue mix above. Let this cure and re drill the holes to the required size; this method ensures you a layer of epoxy right around the hole so no moisture can enter the ply.

Add 6 mm thick backing strips as required, adding some more of the glue mix above and tighten with your fingers then remove any material that is squeezed out. Tighten after the glue has cured.

As epoxy is not UV stable it will require a coat of epoxy primer and paint.

Hope this helps.

Avagoodweekend......
 
you mention epoxy resin as the wood to grp adhesive, isn't 3M 5200 good enough .... no experience of it, but the 3M spec sheet seems to tick all teh right boxes ?

If you thick I should use epoxy resin, can you advise a make ?
 
Tafflad said:
you mention epoxy resin as the wood to grp adhesive, isn't 3M 5200 good enough .... no experience of it, but the 3M spec sheet seems to tick all teh right boxes ?

If you thick I should use epoxy resin, can you advise a make ?
Click to expand...

I would use epoxy throughout to ensure comparability, not many thing will stick to epoxy.

First choice of resin would be West System, available in 4 litre packs.

Hope this helps,

Avagoodweekend......
 
oldsaltoz said:
I would use epoxy throughout to ensure comparability, not many thing will stick to epoxy.

First choice of resin would be West System, available in 4 litre packs.

Hope this helps,

Avagoodweekend......
Click to expand...

so the epoxy, is used as the 'glue' to fix it to the grp, as well as to coat the wood itself ?
Does that mean you can mix it thick or as a paint.
 
Tafflad said:
so the epoxy, is used as the 'glue' to fix it to the grp, as well as to coat the wood itself ?
Does that mean you can mix it thick or as a paint.
Click to expand...

You can use the epoxy as a paint to coat the ply, then thicken it with microfibres to bond the two layers of ply to the (roughed up) GRP, it will adhere. Have a look at the west system website. Epoxy isnt UV resistant, but I surmise this is below the deck, so not subject to direct sunlight?? If its in direct sunlight, a coat of paint will protect it, any paint basically.
 
Tafflad said:
I fitted a Tower to my boat this year, or in fact the dealer did.
I'm very pleased with it.

What I intend doing out of season is laminate in some supports behind the deck fittings, to cut down on flex, and strengthen the support point.

Intent is to glue in some 3mm ply - about 60cm x 20cm been advised, with fixing bolt through the middle. ... that is 1/8" of 24" x 8" for those not yet in 21st Century...

Once glue has set, glue in a second layer over the first.

Advised to use 3M 5200 as the adhesive.

The Q ... should I be using Marine ply for this, or as this is well above the water line, is WBP ply good enough.
I could always put a coat of yacht varnish over the ply & edges once fitted.
Click to expand...



When you say 'Tower', are you referring to:

1) an observation tower on a game fishing boat,

2) a light mast arrangement carrying radome, gps antenna, etc.,

3) ski-boat upper structure with sub-woofer and wakeboard racks.

I prefer to use plate alloy or SSteel as backing plates.
 
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