Laminating your own plywood

[dancrane]

I need a four-foot by eight-inch piece of very stiff ply, but with a slight curve. Given that I can't induce curvature in wood fabricated specifically to resist it, I'm going to try making my own.

The fact that I happen to have a four-foot by two-foot sheet of cheap 5mm ply which already has a suitable bend in it, is a happy coincidence.

It isn't quality plywood, but I'm thinking that the coats of epoxy which will be necessary to glue the 'plies' together, can provide pretty good encapsulation if I take care to coat the end-grain. Also, it won't often be immersed (I hope).

I'll end up with a piece 4ft by 8", about 16mm thick. Or I could cut four six-inch strips, to make a thicker 'plank'.

It needs to be rigid and robust because the plan is to mount an outboard bracket on it. A bit hard to describe till it's done.

Any advice or experience of similar jobs? Thanks.

 

[SvenH]

To get you started:

Good marine ply has better water resistance than cheap, because of the glue and material selection.
My rule for any outside use of plywood is that "if there is a gap, water will find it."

 

[RJJ]

....finish it off with a couple of layers of glass fibre to make waterproof?

 

[coopec]

I need a four-foot by eight-inch piece of very stiff ply, but with a slight curve. Given that I can't induce curvature in wood fabricated specifically to resist it, I'm going to try making my own.

The fact that I happen to have a four-foot by two-foot sheet of cheap 5mm ply which already has a suitable bend in it, is a happy coincidence.

It isn't quality plywood, but I'm thinking that the coats of epoxy which will be necessary to glue the 'plies' together, can provide pretty good encapsulation if I take care to coat the end-grain. Also, it won't often be immersed (I hope).

I'll end up with a piece 4ft by 8", about 16mm thick. Or I could cut four six-inch strips, to make a thicker 'plank'.

It needs to be rigid and robust because the plan is to mount an outboard bracket on it. A bit hard to describe till it's done.

Any advice or experience of similar jobs? Thanks.

If I was going to the trouble of doing that I would use Marine Ply (or at least exterior ply/structural [ply) I'd use quite thin ply - 3 or 4mm. Cheap -ply won't last 5 minutes

 

[john_morris_uk]

I’ve laminated the curve of a coach roof with multiple sheets of 6mm ply epoxied together. It worked very well.

 

[coopec]

I’ve laminated the curve of a coach roof with multiple sheets of 6mm ply epoxied together. It worked very well.

I'm planning to use "bendy ply" to make a dodger. Any thoughts?

 

[Kelpie]

The epoxy will cost the same regardless of what type of ply you use... don't use the really cheap stuff unless it's literally going to be a mould for an outer skin of glass.

 

[Keith 66]

If you use the cheap ply you will just waste expensive epoxy as it will disintegrate just marginally slower.

 

[burgundyben]

If you have not already done so look at tge recent plywood thread in the classic and wooden boat section.

 

[caiman]

Not sure whether you are asking about how to laminate a curve,or the wisdom of using cheap ply to make the curve.
If it's the former,there are loads of films of people doing this on You Tube.There are also loads of written guides on the web.A quick Google will give you many options.Sorry,I don't know how to add a link.
This was how I learnt when laminating beams/gunnels for a 24foot launch I was restoring at the time,the results being very pleasing and functional.ie strong.
If it's the latter,I agree with a post earlier that water will get into anything it can.A (younger than me) wise builder once told me that'Water will make a fool out of anyone',and I have to agree.
On a piece that small.'proper' marine ply would not cost that much,and you might end up deciding to use the ply that you have as part of the table on which to make the jig.
For materials,Fyne Boats in Cumbria are my 'go to guys'.No connection to them except being a very satisfied long term customer.I'm just finishing a replacement transom in a speedy boat using their epoxy/powders.
If you have not done much with epoxy,maybe use the ply you have as a practise run,the epoxy/powder required for that job is not large, will not cost that much,and the experience gained will be worthwhile.
If you are experienced with epoxy then use decent ply,but then if you are experienced you would know that anyway.
Good luck with your project,for a half a days work I feel that you will enjoy doing the job, and be pleased with the outcome.
Hope this helps.
Cheers

 

[Paulg25]

 

[Spirit (of Glenans)]

.Sorry,I don't know how to add a link.

In very simple terms,(because I dont know the name for it), find the line at the top of the page that begins with "http". Highlight it, by putting your cursor at the start, holding down the left button on the mouse and moving the cursor right along the line and just past it, in case there is any code hidden, then hold down "Ctrl" and"c" at the same time. This copies the line.
Then go back to the tab that contains the website where you want to insert the link, make sure the cursor is where you want to place the link, and press "Ctrl"and "v" simultaneously. This "pastes" the link.
I still don't know how to connect a link to words like "here" or "this", like some clever posters do.

 

[Stemar]

My rule for any outside use of plywood is that "if there is a gap, water will find it."

My corollary to that is "Even if there isn't a gap, water will find it"

A sheet of marine ply is a small expense compared to all the rest in a project like that. Ha'p'orths of tar spring to mind.

 

[TernVI]

It sounds like a bit of an experiment.
Gluing those four layers of ply will use maybe 20 quid's worth of epoxy.
Buying a 'nice' piece of ply £££?

A couple of thoughts
You could use the cheap ply that'scluttering up your garage. You could use PVA for the laminating and see how the experiment performs
If you actually want it seriously stiff, then glass or even carbon cloth and epoxy on the outside?

One could use structural foam instead of the plywood, maybe just for the inner layers.
There are a few nice dinghies with wood/foam/??? sandwich decks.

16mm plywood is not super-stiff. Some numerical thought about what is actually required might be enlightening?

 

[Neeves]

As Tern VI suggests I'd use glassed foam and finish with a layer of whatever wood, veneer, you want. I'd make the same suggestion to Coopec, foam and glass, not bendy ply. If you are worried about bending the foam, multiple layers of thin foam works well and you can source foam specifically made to bend (it has a cloth back). Coopec - try ATL composites, based in Old, You can fill and sand out the imperfections relatively easily and then finish with whatever you want, veneer, spray 2 pack....

Jonathan

 

[NormanS]

If you use ply, half the grain will be running across, contributing no strength whatever. Simple to laminate thin strips of solid timber. Think of laminated deck beams etc.

 

[coopec]

If you use ply, half the grain will be running across, contributing no strength whatever. Simple to laminate thin strips of solid timber. Think of laminated deck beams etc.

I want a dodger just like this. I could get a canvas covering made up at a cost. Of course canvas won't add strength ?

I've used Divinycell foam and Airex as well as polyurethane foam before.

The dodger I build must fold down to deck level in the event of storm conditions or the dodger must be sacrificial.(I don't want the deck destroyed when the dodger is carried away by a large wave,

Obviously the dodger pictured has a SS frame to give it strength, Bendy ply with epoxy/cloth on either side should be fine


?

Blu water sailors posting on this forum say they always lower the dodger and stow everything down below during storm conditions.

 

[SvenH]

"My corollary to that is "Even if there isn't a gap, water will find it"
True, it rusts the mild steel staples and then follows the hole that was first occupied by the staple. (In the case of my boats scoop...)

 

[Spirit (of Glenans)]

I want a dodger just like this. I could get a canvas covering made up at a cost. Of course canvas won't add strength ?

I've used Divinycell foam and Airex as well as polyurethane foam before.

The dodger I build must fold down to deck level in the event of storm conditions or the dodger must be sacrificial.(I don't want the deck destroyed when the dodger is carried away by a large wave,

Obviously the dodger pictured has a SS frame to give it strength, Bendy ply with epoxy/cloth on either side should be fine


View attachment 101853 ?

Blu water sailors posting on this forum say they always lower the dodger and stow everything down below during storm conditions.

I'm rather disappointed to read that, as I thought that their chief purpose was to keep the crew dry and prevent rain/spray going down the hatch during inclement conditions. I crewed on a boat which crossed Biscay in a named storm, and subsequently sailed to St. Lucia with my wife on board, without ever taking down either the sprayhood or the bimini!

 

[KompetentKrew]

I want a dodger just like this. I could get a canvas covering made up at a cost. Of course canvas won't add strength ?

I've used Divinycell foam and Airex as well as polyurethane foam before.

The dodger I build must fold down to deck level in the event of storm conditions or the dodger must be sacrificial.(I don't want the deck destroyed when the dodger is carried away by a large wave,

Obviously the dodger pictured has a SS frame to give it strength, Bendy ply with epoxy/cloth on either side should be fine


View attachment 101853 ?

Blu water sailors posting on this forum say they always lower the dodger and stow everything down below during storm conditions.

I have a dodger like that and it doesn't fold down. If the dodger is carried away by a storm, so will my whole boat!