Repairs to plywood deck
 

I have a 25 year old, marine ply 31 footer, in which some cracks are
appearing in the deck (allowing drips to enter above my bunk). I presume
these are where the plywood sheets join - haven't removed any paint yet, so
I'm not sure. Simple question - is it usual for deck joints to be butt
joints, or do people use scarf joints? The former seems more likely if the
joints are always over some form of supporting rib.
TIA.
John.

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"John Seager" wrote in message
...
I'm not sure. Simple question - is it usual for deck joints to be butt
joints, or do people use scarf joints? The former seems more likely if the
joints are always over some form of supporting rib.


It is common for production boats to have the butt joint of deck ply on the
deck beams. However, that doesn't mean it is correct. This is because the
grain of the deck beam provides very little strength across the grain. On a
deck of single ply, a scarf or ply butt block between deck beams would be
the correct method.

If the decks were double layers of ply with joints well spaced, then a butt
joint on the deck beam might be expectable since the upper ply acts as the
butt block.

I have never favored plywood scarf's in plywood of less than, say, 1/2" and
then only if it is 5 or 7 ply. Also, marine ply is much better suited for a
scarf joint because of the more uniform ply thickness and absence of voids.

My opinion and experience. FWIW.

Steve
s/v Good Intentions

"Steve" wrote in message
...
It is common for production boats to have the butt joint of deck ply on
the
deck beams. However, that doesn't mean it is correct. This is because the
grain of the deck beam provides very little strength across the grain. On
a
deck of single ply, a scarf or ply butt block between deck beams would be
the correct method.

Thanks, that makes good sense. I'm pretty sure that my boat has a single
thickness of ply (around half inch). There seem to be quite a few of these
cracks - small, but enough to create leaks - so I guess I should cut out and
replace the offending pieces. Although I like the elegance of a scarf joint
I don't think my woodworking skills are sufficient to be sure of a good
joint so butt joints seem the obvious way to go but with a butt block, as
you suggest. However, I'm also tempted to think that careful application of
epoxy in the cracks, might be a possible compromise. Sorry if such a
suggestion is heresy to those who believe that wooden boats should be made
of wood!
John.

"John Seager" wrote in message
...
"Steve" wrote in message
...
It is common for production boats to have the butt joint of deck ply on
the
deck beams. However, that doesn't mean it is correct. This is because the
grain of the deck beam provides very little strength across the grain. On
a
deck of single ply, a scarf or ply butt block between deck beams would be
the correct method.

Thanks, that makes good sense. I'm pretty sure that my boat has a single
thickness of ply (around half inch). There seem to be quite a few of these
cracks - small, but enough to create leaks - so I guess I should cut out
and
replace the offending pieces. Although I like the elegance of a scarf
joint
I don't think my woodworking skills are sufficient to be sure of a good
joint so butt joints seem the obvious way to go but with a butt block, as
you suggest. However, I'm also tempted to think that careful application
of
epoxy in the cracks, might be a possible compromise. Sorry if such a
suggestion is heresy to those who believe that wooden boats should be made
of wood!
John.


John
I'm also trying to strike a balance between spending time using my '59
wooden boat and time spent fixing it. Have to say I'm not spending much
time using it at present, and it's mid summer down here ...
I'm tending to the epoxy repair path, for similar reasons. But I'd be
asking another question. If the water has penetrated between the edges of
deck ply sheets, where else has it gone, what other damage has it done?
Unless the edges of the sheets were perfectly sealed, I'd not be surprised
if there is some softening and/or rot.
I hope my theory of wooden boats does not apply in this case - I figure that
generally whatever you think the problem is, the reality will be 400% worse
.....

Regards
David

"David Flew" wrote in message
...

Unless the edges of the sheets were perfectly sealed, I'd not be surprised
if there is some softening and/or rot.

Yes, I'm sure this is a strong possibility, although it feels quite solid
for the most part. I guess I'll have to start scraping and if there's more
wood than rot, I'll use epoxy. If it is rotten, it will call for
replacement.
John.

On Fri, 28 Jan 2005 10:18:28 +0200, John Seager wrote:

"Steve" wrote in message
...
It is common for production boats to have the butt joint of deck ply on
the
deck beams. However, that doesn't mean it is correct. This is because the
grain of the deck beam provides very little strength across the grain. On
a
deck of single ply, a scarf or ply butt block between deck beams would be
the correct method.

Thanks, that makes good sense. I'm pretty sure that my boat has a single
thickness of ply (around half inch). There seem to be quite a few of these
cracks - small, but enough to create leaks - so I guess I should cut out and
replace the offending pieces. Although I like the elegance of a scarf joint
I don't think my woodworking skills are sufficient to be sure of a good
joint so butt joints seem the obvious way to go but with a butt block, as
you suggest. However, I'm also tempted to think that careful application of
epoxy in the cracks, might be a possible compromise. Sorry if such a
suggestion is heresy to those who believe that wooden boats should be made
of wood!
John.

I don't have too much experience with wood boats, but I know that even
epoxy won't hold together two pieces of wood that are trying to shrink
apart.

Also, it seems to me that if the deck was watertight for 25 years and now
has leaks in several places, there might be something (bad) happening to
it. Maybe moisture has started to get in, so the wood is shrinking due to
wet dry cycles, or maybe it is sagging slightly in between the
deck beams, causing these on-beam butt joints to pull apart?

--Mac