: Welcome Mark, glad to have you aboard. There is a good deal of interest in
: vacuum bagging here; not that many people have tried it. I'm tempted to
: bag my next hull but I'm not sure how to handle the point where the glass
: meets the mastic. . .

There are some points made elsewhere in this thread about using vacuum to suck out air from the wood and to improve its saturation with water before steaming, but for the most part I think what we want from vacuum bagging are just two characteristics:

1) A clamp-like compression to hold the fabric close to the wood. This keeps the fabric from floating and is particularly sought after when laying up very thin cloth 9 which floats esaily) or multiple layers of cloth (which can BOTH float).

2) A smooth (peel ply) finish which levels any resin on top of the fabric, reducing the need for more coats of resin to fill in the pattern of the weave. This saves weightand material (You don't need that extra coat of resin) and time (one or two less coats to put on)

With polyester resins there is the additional benefit that the resin hardens on the surface if air is missing -- but we don;t use a lot of polyester resin.

I think we may be able to achieve these two attributes without the hardware of a vacuum system if we simply replace the plastic vacuum bag with a plastic bag made from heat shrinkable plastic. the cost for the materials should be fairly close, and heat shrinking boats is now a fairly common practice, so the materials are available through boating supply stores.

The process would be: measure out the necessary shrinkwrap plastic, and assemble and heatseal the edges as much as you can in advance, then pull the thing offthe boat and set it aside. apply the resin and glass fabric, aiding the wetout with a squeegee. slip the bag bac over the boat, finish sealing the edges, and heat it gently over all so that wrinkles are removed and it shrinks down firmly. Walk away and let the resin set up.

No pumps, no tubes, no peel ply, no bleeder/breather fabrics, no extended electric cords to trip over.

The shrink wrap will pull tightly, but not with anywhere near the pressure you would have with a vacuum system. This should be enough to prevent floating fabric, and to give a smooth finish. The pressure will be light enough that you can shrink wrap a boat while it is still on the forms, or, just a hollow hull without forms in it.

Downsides: This won't do a thing for the inside of the boat or any concave areas, and it will be of little help on any relatively large flat areas. It would really work best just for doing the outside of a fairly rounded hull.

Just a thought

PGJ