Urgent Help..is my Marine Ply OK...

[fwalschots]

Hope you guys can help.

Just had a supply of 10mm Hoop ply delivered yesterday. When the ply was unloaded it was slightly warped and the dist said that it was slightly bent because the sheets had been standing up.

I layed the sheets flat and weighted them, however they still don't lie flat. To me it feels like the Ply has stresses within.

When you lift it holding the corners and you flex it, the sheet flips from diagonal to diagonal. You can distincly feel the point when the stress changes from corner to corner.

The sheets are stamped as 1st grade Marine to Australian standard.

Do these sheets have internal stresses or will they flatten out.

Your opinons needed urgently.

[Stiletto]

If you are reasonably close to the supplier and can go and inspect their stock , I would consider doing that with a view to exchanging it it if possible. I would have some reservations about buying ply from a supplier that stores it on edge, as it shows a lack of understanding of the product and the customers needs.
Sheet products stored on edge develop a curve along the length rather than the diagonal you mention.
You say there is a slight warp -How slight? Remember that you will be cutting the sheets to a smaller size to fit your boat so the distortion may be fairly insignificant.
Get a few beers, kick back and watch Bathhurst, thinking about it might be the worst part.

Good luck .

[NormMessinger]

What are you building? My guess is that by the time you cut your boat? parts to size and nail them in place you won't know the difference.

[fwalschots]

Stilleto...

When you lie the panels down, the curve is from diagonal to diagonal rather than the straight edge. The corner lifts approx 10mm and then when you flex the other corner lifts.

The supplier is about 1200kms away, I bought the ply through the Boat Craft agent here in Canberra. I will try and ring the supplier on Monday...

Maybe I am concerned over nothing. When a boat has enough stresses in it already I don't want to add to this with 'stressed Ply'.

[fwalschots]

Norm.
I'm building a Cape Henry 21. I am not worried about panels being bent, just if this ply has internal stresses then I have been sold seconds, not first qulaity that I paid for.

cheers

[George Roberts]

fwalschots ---

What you have is typical of plywood. The stresses are not important.

[JimD]

I agree with George.

[Bob Smalser]

You can flatten it with weight and more time.....but what you describe doesn't sound like anything I wouldn't just go ahead and use.

[ 10-11-2003, 09:26 PM: Message edited by: Bob Smalser ]

[fwalschots]

Thankyou guys for your words of wisdom.

Ply is a new medium for me, we didn't use it my professional furniture making days, then if we found wood with internal stresses we discarded it as not suitable for cabinets, tables etc.

cheers

[NormMessinger]

The best plywood will take a set if it is not stored flat. It could be made to give up that set if you could apply an opposite bend of the proper amplitude and time. Once the plywood is in place on your boat, whether it is flat or not when you put it on, it will take a set according to the shape of your boat. No worries. Use the existing set to your advantage.

[oldriverat]

Have you ever seen a board or sheet of ply that was left laying out in the elements? It will almost always develope a curvature with the ends pointing up. You can lay the sheet of ply in the grass, with the concave side down, on a warm summer day. It will absorb moisture from the ground and straighten out. Keep an eye on it. Sometimes it only takes about fifteen minutes. If you leave it too long it will warp the other way.
In the winter, a sponge bath on the concave side and heat from the shop stove will do the trick.
It worked for me smile.gif

[Banjo]

[QUOTE]Originally posted by fwalschots:
Hope you guys can help.

Just had a supply of 10mm Hoop ply delivered yesterday. When the ply was unloaded it was slightly warped and the dist said that it was slightly bent because the sheets had been standing up.

I am also using Hoop Pine sheets, I decided to go for the cheaper grade, it's still just as good. It has one less veneer but the glue is the same as yours, cost was 1/2 that of marine stamped ones.

You will always get ply bending one way or another even if stored flat, the ambient moisture content of the air will cause the top sheet to bow because the upper lamination will absorb moisture thus expand a little more than the underside laminations.


I layed the sheets flat and weighted them, however they still don't lie flat. To me it feels like the Ply has stresses within.

What you have done is correct, but also add a spare sheet of anything on top to help stop some moisture getting to the top sheets outer lamination. All good sheet distributors should have the sheets stored flat in racks with a cover sheet on each stack. Mine were stored that way as I picked them up myself and got to see their storage system, even so my sheets still have twists in them as you describe.


Do these sheets have internal stresses or will they flatten out.

All organic material will have some sort of internal stresses, even us! smile.gif But in youre case don't stress. Once you cut the sheets to their sizes needed the stresses will not be a problem. They will end up under more stress when you bend them to the boats lines ayway and in a short space of time they will forget all about the previous shape they prefered...

Just another thought, isn't the Cape Cutter strip planked? I take it the 10mm sheets are for the hull planking. Lovely boat by the way, I loof forward to keeping up with your project as it grows.

[fwalschots]

Thanks guys...

Banjo, the Cape Cutter19 and the Cape Henry21 (what i'm building) is ply lapstrake. You can be assured that I'll keep the forum posted of my progress and hopefully some pics.

cheers