On 15 Jul 2007 13:50:50 +1000, GB
wrote:

Bruce wrote in
news
I'm not sure how you plan on building this boat but for a small dinghy
I'd use the "stitch and glue" method where you cut the various panels
to size and tie them together with wire, cable ties, strong string,
whatever, and then smear glue in the joints.

I'd looked at similar approaches used on various web pages and
was concerned that the method didn't look nearly strong enough.
The design I had in mind was flat bottomed, (see the url below)
and I had planned on perhaps going beyond the reccomended jointing
methods screwing the bottom and sides to a piece of wood of
about 1in x 1in for the length of each join. Is that overkill?


[...]
If you are interested in a really good small dinghy do a web search
for a "D4" dinghy. The plans are free and the guy's web site has a
wealth of information on building boats.

That D4 does look like a very nice little boat. A bit more advanced
than what I had in mind though. Something like this:

http://personal.eunet.fi/pp/gsahv/dinghy1/simboii.htm

is where I'd planned to start. If that works out OK, then this
D4 design looks like a good next step!


Thank-you,


GB

Actually a properly made "stitch and glue" joint is probably stronger
then using a batten to screw to. Remember that there is a epoxy filler
fillet, usually about a half by half inch at each place the plywood
joins, which is then covered with a 4 inch fiberglass tape. I tape my
joints both inside and outside, which may be over kill, and while I
have never actually tested one to destruction I am willing to bet that
the joint is stronger then the parent plywood.

Of course it is your boat and you should build it the way you think
best but do take into consideration that literally thousands of stitch
and glue boats and if the method wasn't effective certainly there
would be comments all over the net.


Bruce in Bangkok
(brucepaigeatgmaildotcom)

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"GB" wrote in message
...
completely ineffective on others, etc, etc. I have a bit of
difficulty with the concept of a near-solid (as in almost brittle)
epoxy contributing any sort of strength to a butted joint between
two bits of ply. I'm not saying it won't work, just that it
conflicts with my own experiential knowledge of how things 'work'.

Well, take a look at this dinghy: www.customware.nl/boats
It is entirely glued together. Not a singe screw and even the skeg (20mm)
wide is simply glued to the keel.

I once did a test: everone keeps telling me that oak doesn't glue well with
epoxy so this was a good starting point for my experiment. I sanded the oak
with grit 40 across the grain, applied some epoxy and let it cure without
clamping.

Next day I drove a 3/16" nail straight through the seam, trying to break the
epoxy. It didn't. the wood around the nail gave up eventually.

My own exposure to fibreglass is limited to canoe-building class
in high school. Those were well before OHS days, so we were all
so high on the fumes that there wasn't much consciousness left
to develop a feeling for just how strong a fibre-tape/epoxy
join might be!!!

Epoxy does not produce fumes. You're mixing it up with polyester.

Meindert

On 16 Jul 2007 22:18:28 +1000, GB
wrote:

Bruce wrote in
:
Of course it is your boat and you should build it the way you think
best but do take into consideration that literally thousands of stitch
and glue boats and if the method wasn't effective certainly there
would be comments all over the net.

I agree. I'm not questioning the method so much as questioning
my own knowledge of what works and what doesn't. I grew up in an
environment where tradesmen were never called, we figured out and
fixed /everything/ ourselves, be it plumbing, home extensions,
electricals and electronics. I've kinda developed a bit of a
feel for materials, and what works and what doesn't. You know,
certain types of glue will fix certain materials, and will be
completely ineffective on others, etc, etc. I have a bit of
difficulty with the concept of a near-solid (as in almost brittle)
epoxy contributing any sort of strength to a butted joint between
two bits of ply. I'm not saying it won't work, just that it
conflicts with my own experiential knowledge of how things 'work'.

On PVA type glues, I'm very much aware (and continually
amazed) by just how strong a join that stuff makes between two
pieces of timber, but again, I have conceptual problems with
using it on a join that's designed to be dunked in a pond!

My own exposure to fibreglass is limited to canoe-building class
in high school. Those were well before OHS days, so we were all
so high on the fumes that there wasn't much consciousness left
to develop a feeling for just how strong a fibre-tape/epoxy
join might be!!!


Hence all the questions! I'm sailing (pardon the pun) in
uncharted waters!


Thanks, I appreciate your comments.


GB

Try the epoxy before you ignore it.

Make a 90 degree butt joint with 1/4 inch plywood and glue it with
epoxy. Mix up some epoxy and some sort of filler, sanding dust from
the same kind of wood you are glueing works fine, and form a fillet
approximately 1/2 inch wide on the inside of the 90 degree joint, Then
wet out a 4 inch wide piece of glass tape with epoxy and place that
over the fillet. Roll out any bubbles and let it harden for 48 hours
and then try to break it. Twist it, pry it, whatever you want, and
you'll find that the plywood fails long before you can break the joint
itself.




Bruce in Bangkok
(brucepaigeatgmaildotcom)

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