No Spam wrote:
"Tinkerntom" wrote in message
oups.com...
Snip

Ken, the only thing I would question, is that where the dowel comes
out
of the pipe, would represent a sheer line. All the load on the
extended
dowel would be concentrated at the sheer line as a breaking force.
You
would not be able to take advantage really of the flex of the dowel
inside the tube, to dissipate the energy as a flexing force, and it
would tend to break at that sheer line.

You are right on though about hearing the dowel break.

Another function of the safety line that I recommended, is that if
the
extension collapses, the boat would not fall clear to the ground.
Considering the car paint though, it might be equally important to
use
some cushions in strategic spots in case the boat fell. You could
just
hang a long noodle on the side of the car to take the bang.

or like Cyli indicated, you just don't worry about the paint!
TnT


You are correct about the shear at the point of entry but I think a
hardwood
dowel of this size will take this force without complaint. My uncle
used to
hang an old wood extension ladder on dowel pegs and it took 2 people
to lift
that thing down. The flex in the exposed dowel would take the force
of the
jolt of rough handling of the boat though. I did some google
searching but
cannot find the shear strength of a dowel but I would guess that a 1
inch
hardwood dowel would take at least 500 pounds of pure shear force
before it
would break. I have a 1 1/2 inch dowel here and I just stood on the
end of
it with the other end wedged under my work bench -- yep lifted the
bench
right up - the dowel flexed a little but easily handled me 275 lbs
out about
a foot from the support.

Ken

Ken, Wilf, is talking about extending the dowel out 28", see what
loading the dowel breaks under now. This will prevent Wilf from falling
off his workbench, and you seemed more inclined to do this sort of
stuff! I mean testing, not falling off your bench! TnT