: I don't think I would try to bag the exterior of a boat still on forms. The
: bag has to have a really good seal, or leakage will prevent getting a
: decent vacuum.

assuming that you do the fiberglass in the standard order (outside hull, inside hull , outside deck, inside deck) you should have to start the bagging with the forms still inside. I would imagein that the fill coat will deal with most of the pinhole leak issues. if not yoo should be able to stop the ingassing with something like saran wrap (tm), especially if you think ahead and station the forms a saran wrap's width apart.

: The pumps are low volume. In order to get a good enuf seal,
: I think you would need a full poly layer INSIDE the boat extending beyond
: the gunwale to seal the exterior bag to.

Ideally you have a drip catch, and a large vac tank inline with you pump, this will allow you to lessen the work required by the pump. I have also heard of people pumping out hte vac tank before attaching the vac lines to the bag, this allows for faster seeling of the mastic(?) to the substrate.

: To me, the REAL benefit comes
: on the interior of a decked kayak, where you can bag it, and then NOT fill
: it (except for possibly a very thin coating to seal any pinholes, a step
: which MAY not be necessary with vac-bagging). And, on the interior, you
: have the exterior glass already on, so an exterior bag is not necessary. I
: think (disclaimer) you could just wrap the poly bag around the edge and
: tape it to the cured glass on the exterior.

going stright to vac-bagging without a fill coat _may_ result in a very light layup, but would _may_ result in a not allowing any eposy to wick into the wood. when this happens in a normal layup the expoy will sometimes wick into the wood away form the glass, leaving a point of no bonding action. or the rising tempature will cause the expanding gasses to push the expoy out of the wood, also leaving a point of no bonding action. I worry about the vac bagging teqnique interfering with the normal capilary (capilitory?) action of the wood causing possible delamination weakness.

the real benifite will be getting the glass to sink (ie not float) into the corners and fillets on the inside of the hull and deck.

: I haven't begun building a yak. But I do aspire to ... and daydream about it.

I am working on my second kayak. as a disclamer I have not done any vac baging work yet, but have been reading about it in preperation