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0_Qed wrote in message ...
Backyard Renegade wrote:

(Graaeme) wrote in message . com...
I have been restoring a plywood boat approx 20yrs old & have noticed a
ridge in one sheet of ply running accross the sheet in a uniform
manner. I have removed paint down to the wood & everything seems OK,
no sign of damp or delaminating.
Is this quite normal for ply to do this or could there be an
underlying fault? If so is it best to just ignore it as it just seems
cosmetic to me. By the way its nowhere near the end of the sheet or
any other obvious weak point.

Thanx,
Graeme

My best guess is that it is a void in the under plys of the plywood.
Probably ran the full width or length of the plywood when the boat was
built. If it is visible from the top ply it is probably in the second
ply of the stock and origionally ran across the width of the plywood
or formed as the interior core ply expanded and contracted over the
years.... more likely it was there from the start though. The moisture
and air content behind that area is different than the rest of the
face so it ages, takes and releases moisture, etc, etc,... different
than the rest of the face, makes a "nice" line across your boat.
When building with exterior grade material, I look very closely for
these voids, they are indeed weak spots and on thinner plywood with
only three plys, they can lead to a crack out of the hull. Many times
you can hear/feel these voids if you run your hand across stock at the
lumberyard or look for the tell tale signs.
All this being said your boat having lasted this long was probably
designed and built with exterior ply in mind, it is probably just
cosmetic as you suggest, paint it nice and let er rip...
Scotty from SmallBoats.com

:-)

Most probably a " core lap " ...

Caused during the 'lay_up' of the indiv sheet ...
the core_layer ( person or machine ) over_lapped two adjacent pcs of
veneer ...
most typically the ply directly under the face or the back veneer ( 5
ply ),
or ...
the mid veneer in a 3 ply construction ...

If its 'exposed' to the water "side" ... not the best condition ...
a big NO-NO in a big hydro ...
live with it in a day sailer.

Sanding, after hot pressing, "tends" to temporarily hide the 'lap' ...
but, the sanding operation does reduce the face ply directly over the
'lap' ...
some lost strength in an important 'ply' ... the face ply.
Repeated wet/dry cycles accentuate the lap over time ...

A 'cause' for =must rejection= at a good state-side mill ...

Ahhh, your guess makes more sense based on his origional
discription... I was thinking the wood was more swolen there because
of a void behind it, I did not think about overlapping. Still all in
all sounds cosmetic.
Scotty from SmallBoats.com

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