I haven't bagged a canoe but I have done a considerably larger hull. It
is not all that hard but not really necessary for a canoe. A well
rolled and squeegeed job will work very satisfactorily with far less work.
You will first need a pump. For a canoe I would guess something with a
2 or 3 cfm rating would suffice. Unless you have a healthy compressor a
mechanical pump would be much preferred to a venturi. YOu can find a
suitable pump on ebay for under $50 fairly often. A needle valve to
control the vacuum is important and a $5 vacuum gauge from Northern
Tools would be helpful.
You will need some 3 or 4 mil poly sheet and a few feet of nylon tubing
from the hardware store, some nylon taffeta or flag bunting from a
fabric store to act as a peel ply and an old polyester blanket for a
breather/bleader. Test the taffeta first to make sure that it will not
bond to the epoxy very strongly. Sometimes the sizing causes a problem.
The only thing you really need to get from a specialty store is the
vacuum tape. It is about 1/8"x1/2" gummy material that will stick to
the poly. It comes with a treated paper backing on one side.
The simplest way to bag the hull is to run a couple of extra strips
above the shear line (actually below if still upside down on the molds).
These strips can be any cheap clear wood cut to the same thickness as
the hull strips. Before starting to glass apply the vacuum tape around
the extension and cover with 2" masking tape to keep epoxy from dripping
on it.
Once the glass is in place and wetted out, cover with the taffeta and
trim it just above the masking tape. Follow with the blanket. Cut a
square of blanket about 3x6" and fold it over. Tape it in place about
midship at the keel. (more on this later) Lay the poly sheet in place as
evenly as possible, trim to 3 or 4" below the masking tape and remove
the masking tape. Cut the tape backing about mid ship and peel off
about a foot. Press the poly onto the tape and work towards the ends
peeling a little backing and smoothly pressing on the poly.
When you get both sides sealed you will have a big loop at the bow and
stern. Pick up the loop and pinch it together directly above the bow so
that both sides are even. Trim directly down to about 2" past the bow
and measure the distance from the fold to the tape. Cut another piece
of tape about 2" longer than that. Starting about 1" past the pinch,
apply the tape over the pinch and down one edge and join it to the lower
tape. Holding the pinch seal both sides smoothly together. Repeat at
the stern.
Cut a small hole in the poly in the center of that extra pad of blanket
material and insert the nylon tube. Seal it with a ring of vacuum tape
and turn on the pump.
Any wrinkles will leave a ridge of resin. As the bag draws down, smooth
out the bag bu massaging it down towards the sheer. Pull the pleated
ends up and let the bag come together right at the hull. Once the
vacuum reaches about 5" start checking for leaks and press down the tape
one more time paying particular attention to any small wrinkles. Bring
the vacuum up to about 10" and adjust the needle valve to maintain that
pressure. Don't go any higher or you will squeeze out to much resin.
Let the pump run for 3 or 4 hours. I feel the epoxy left on the mixing
stick to estimate the cure state. You can turn off the pump any time
after the resin is firm but but can still be dented with a fingernail.
Leave the bag in place over night but don't leave the peel ply on
more than about 36 hours. Epoxy goes through a brittle stage before it
develops full strength so the peel ply is easier to remove then.
Remove the bag and find a place to start stripping the peel ply and
blanket. Ideally you want to peel towards or along the edges. At the
brittle state the epoxy is still rather delicate so peeling up from the
edge runs the risk of lifting glass off the hull. It can't be avoided
to start but once you have enough off peel down the length of the hull
rather than across. Also, if you are using biaxial knotted fabric like
DB170 peel across the top yarns to prevent any lifting.
That is a bit longer than I intended bu hopefully it will be useful.
Roger Martin wrote:
> Anyone ever tried doing this?
>
> Results, failures, how to?
>
> All thoughts gratefully accepted.
>
> Regards.
>
--
Glenn Ashmore
I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: <a style='text-decoration: underline;' href="http://www.rutuonline.com" target="_blank">http://www.rutuonline.com</a>
Shameless Commercial Division: <a style='text-decoration: underline;' href="http://www.spade-anchor-us.com" target="_blank">http://www.spade-anchor-us.com</a><!-- ~MESSAGE_AFTER~ -->
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