Graduating to my first multi-sheet stitch-n-glue... butt joints with blocks
are ugly, scarfing will throw off my sheet layout. Can I use a plain butt
joint, supported on both sides by glass and epoxy?

Chuck

On Sat, 29 May 2004 15:43:35 GMT, "Chalatso"
wrote:

Graduating to my first multi-sheet stitch-n-glue... butt joints with blocks
are ugly, scarfing will throw off my sheet layout. Can I use a plain butt
joint, supported on both sides by glass and epoxy?

Chuck

Reassure yourself with a test strip say 3 X 12 inches bonded on the
narrow side to another similar piece. Tape both sides.
Then bend to failure.

Did it fail at the joint?
The method is no good.
It failed in the plain ply? Good!

This test is more authoritive than any post you may read here.

Brian W

yes that is the prefered method on many boats. Contact your designer and
ask what material you should use.

--
Matt Langenfeld
JEM Watercraft
http://jem.e-boat.net/

Chalatso wrote:

Graduating to my first multi-sheet stitch-n-glue... butt joints with blocks
are ugly, scarfing will throw off my sheet layout. Can I use a plain butt
joint, supported on both sides by glass and epoxy?

Chuck

"Brian Whatcott" wrote...

Graduating to my first multi-sheet stitch-n-glue... butt joints with
blocks
are ugly, scarfing will throw off my sheet layout. Can I use a plain butt
joint, supported on both sides by glass and epoxy?

Reassure yourself with a test strip say 3 X 12 inches bonded on the
narrow side to another similar piece. Tape both sides.
Then bend to failure.

Did it fail at the joint?
The method is no good.
It failed in the plain ply? Good!

It probably depends also on how the joint will be stressed. If it's in an
area where bending stresses are minimal, it may work just fine. However, if
it is subject to repeated bending loads, it may eventually fail. Also, if
the joint is marginal to begin with, quality control is critical -- make
sure your production pieces are AT LEAST as good as your test pieces.

A compromise may be to use several layers of tape at the joint,
appropriately beveled, to spread the load further. The final layer of cloth
over the hull will add to the strength.

Another consideration is how the boat will be finished. If it's to be bright
(varnished), then a carefully done scarph is the best choice. If painted, a
taped butt, as at http://www.instantboats.com/images/buttjoint700.gif , is
OK. I'd suggest cutting the cloth on the bias, so that all of its threads
cross the joint.
With a little practice, the scarph takes less time.


Chalatso wrote:

Graduating to my first multi-sheet stitch-n-glue... butt joints with blocks
are ugly, scarfing will throw off my sheet layout. Can I use a plain butt
joint, supported on both sides by glass and epoxy?

Chuck

"Jim Conlin" wrote...
Another consideration is how the boat will be finished. If it's to be
bright
(varnished), then a carefully done scarph is the best choice. If painted,
a
taped butt, as at http://www.instantboats.com/images/buttjoint700.gif ,
is
OK. I'd suggest cutting the cloth on the bias, so that all of its
threads
cross the joint.

I taped butt can look good, too. Pygmy uses them on their kayak kits.
Maybe not as elegant as a scarph, but still in character for the boat.

What weight of glass is used? I've found taht its very hard to get glass over
8-10 oz. not to be cloudy.

John R Weiss wrote:

"Jim Conlin" wrote...
Another consideration is how the boat will be finished. If it's to be
bright
(varnished), then a carefully done scarph is the best choice. If painted,
a
taped butt, as at http://www.instantboats.com/images/buttjoint700.gif ,
is
OK. I'd suggest cutting the cloth on the bias, so that all of its
threads
cross the joint.

I taped butt can look good, too. Pygmy uses them on their kayak kits.
Maybe not as elegant as a scarph, but still in character for the boat.

Well, the boat is the bateau.com "cheap canoe," and they suggest a butt
joint, with a block glued over the butt. I think the method suffers a lot
for looks. The joint is right across the fattest part of the canoe, exactly
at the middle. There's added stiffness in the sides from a rubrail, and I
might add a little inwale and a bottom runner, if the taped butt makes me
nervous.

Chuck

It probably depends also on how the joint will be stressed. If it's in an
area where bending stresses are minimal, it may work just fine. However,
if
it is subject to repeated bending loads, it may eventually fail. Also, if
the joint is marginal to begin with, quality control is critical -- make
sure your production pieces are AT LEAST as good as your test pieces.

A compromise may be to use several layers of tape at the joint,
appropriately beveled, to spread the load further. The final layer of
cloth
over the hull will add to the strength.

"Jim Conlin" wrote...
What weight of glass is used? I've found taht its very hard to get glass
over
8-10 oz. not to be cloudy.

Light tape (2 oz?) on the joint, with 6 oz glass over the entire hull. No
clouds after 4 years...

Since the inside of the butt is hidden, a wood block is used on 1 side for
strength. Though it does cause a minor straightening of the curve in the
hull, it is not detectable except under close scrutiny.


John R Weiss wrote:

I taped butt can look good, too. Pygmy uses them on their kayak kits.
Maybe not as elegant as a scarph, but still in character for the boat.

"Chalatso" wrote...
Well, the boat is the bateau.com "cheap canoe," and they suggest a butt
joint, with a block glued over the butt. I think the method suffers a lot
for looks. The joint is right across the fattest part of the canoe,
exactly
at the middle. There's added stiffness in the sides from a rubrail, and I
might add a little inwale and a bottom runner, if the taped butt makes me
nervous.

You might be able to make it a bit more elegant by tapering the block edges.
From the photo of the NC16 on the site, the thwart will draw a lot of
attention away from the blocks. Also, I note they say the blocks may be
made from fiberglass, so a thin strip of tape, followed by a couple layers
of cloth built up with feathered edges may work out just fine.

From the curve of the hull, it appears the tensile stress on the outside of
the hull (where they show no blocks) will predominate over the compressive
stress inboard. Also, if the thwart is glassed in, it will help
considerably in stabilizing the joint. You might also add a fillet or block
under the edge of the thwart, if not already in the plans.

If you're going to paint it, using Kevlar instead of glass may provide more
stiffness with less build-up...