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

Backyard Renegade wrote:
....snip...

Ahhh, your guess makes more sense based on his origional
discription...

Not a 'guess' ... :-)
Several years in the Doug Fir plywood indy ... QC function ...
MS in Wood Tech too ...



I was thinking the wood was more swolen there because
of a void behind it, I did not think about overlapping.

:-)
Core "Voids" are yet another consideration ...


Still all in all sounds cosmetic.

- Core Laps -
Sorry ... not 'so', at all.

In a sanded panel ...
it seriously degrades the bending modulus along(with) the face_ply
grain...

'Fresh' out of the hot press ... hard to visually see

In sanded panels , a bit easier to 'see' ...
*if* you're familiar with samded face_ply wood 'grain' patterns .
Some core-laps in sanded 3/4" cause the face-ply to be
sanded =entirely= thru ...
primarily due to the 'construction' ...
face/back = 1/8" ven
2 cross plies, 1 center ply = all of 3/16" ven
ttl = 5 plies ; 13/16" +\-
Envision a laped 3/16" cross ply going thru a sander .

Most scarfed panels are =rigorously= inspected along the panel edge
for just such 'defect' ... panels are rejected =prior= to scarfing ...

Perhaps an 'exception' mite be un_sanded sheathing grades ...

Floor underlayment is not an exception ... esp "PTS" grades

HTH

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

Ahhh, your guess makes more sense based on his origional
discription...

Not a 'guess' ... :-)
Several years in the Doug Fir plywood indy ... QC function ...
MS in Wood Tech too ...



I was thinking the wood was more swolen there because
of a void behind it, I did not think about overlapping.

:-)
Core "Voids" are yet another consideration ...


Yes, core voids is what I was referring to...



Still all in all sounds cosmetic.

- Core Laps -
Sorry ... not 'so', at all.

In a sanded panel ...
it seriously degrades the bending modulus along(with) the face_ply
grain...

When I suggested it was only cosmetic, I was taking into consideration
the idea that it had been in service for nearly 20 years with no
considerable degradation of the vessel... I am also assuming that the
builder was aware of the defect and as many of us do now (with the
****ty plywood available today) carefully place these defects in areas
where they are not going to effect the strength of the boat or the
integerity of the structure itself..
Scotty from SmallBoats.com




'Fresh' out of the hot press ... hard to visually see

In sanded panels , a bit easier to 'see' ...
*if* you're familiar with samded face_ply wood 'grain' patterns .
Some core-laps in sanded 3/4" cause the face-ply to be
sanded =entirely= thru ...
primarily due to the 'construction' ...
face/back = 1/8" ven
2 cross plies, 1 center ply = all of 3/16" ven
ttl = 5 plies ; 13/16" +\-
Envision a laped 3/16" cross ply going thru a sander .

Most scarfed panels are =rigorously= inspected along the panel edge
for just such 'defect' ... panels are rejected =prior= to scarfing ...

Perhaps an 'exception' mite be un_sanded sheathing grades ...

Floor underlayment is not an exception ... esp "PTS" grades

HTH

Backyard Renegade wrote:
....snip...
Core "Voids" are yet another consideration ...
Yes, core voids is what I was referring to...

'All things considered' ... :-)
voids arent as detremental as laps
BUT ...
in a 3_ply panel I'd not use it if the void( edgewize panel view )
was more than 0.75" x "panel_width", in a sanded 1/4" panel ...
Maybe make 'that' 0.50" ... :-)


When I suggested it was only cosmetic, I was taking into consideration
the idea that it had been in service for nearly 20 years with no
considerable degradation of the vessel...

On a larger hull ... 20' + ...
assuming UN_glassed exterior ... just painted plywood.

With out 'jigging' up the hull , torqueing it ... :-)
to see how the panel with the lap in it performed ...
I'd be leary of not repairing what I'd just discovered ... a lap.
Epoxy 'in' a backer panel, in side the hull ...
6" overlap, both sides of the core_lap , panel face 'grains in
same direction ... "AC" ext grade in same panel thickness


I am also assuming that the builder was aware of the defect

Not many folk inspect every edge, of every panel, going into a boat
hull.


and as many of us do now (with the
****ty plywood available today) carefully place these defects in areas
where they are not going to effect the strength of the boat or the
integerity of the structure itself..

Stick with Doug Fir(DF) plywood , exterior( marine grade ? ) ...
and mills that make 'scarfed' panels ...
Improves your chances of getting 'quality' panels ...
I'd even go so far as to locate an 'inland' DF mill source ...
as opposed to a coastal mill ...
"nicer" wood. :-)


Off -shore 'stuff' I dunno ...
I'd want to sample, & boil-test, the glue lines before I 'purchased'
for a boat hull .

I'd even go so far as to locate an 'inland' DF mill source ...
as opposed to a coastal mill ...
"nicer" wood. :-)

how much of a difference does the coast/inland factor affect the quality of
timber? A timber supplier here in the UK supplies US Doug Fir but specifies
whether it is coastal or inland which made me curious about their relative
qualities particularly with regard to a boat building application.