Builders' Forum Archives
Re: Vacuum Bagging Decks
Posted by John Beck on Nov 6, 2007
I've never vacuum bagged, but here is what I think would happen.
I do know that the practice requires a form to provide 100% support of the the material being glued down (which the deck does not have; more on that later) and a sealed volume. Putting a plastice sheet over the deck and sealing it to the topsides with mastic would seal the outside, but the inside of the joint between the deck and topsides would also need to be sealed. You could seal the underside of the deck to topsides in the cockpit and around the top edges of the front and rear bulkheads. You could not, however, seal along the shear clamp between the bulkheads and ends of the boat. Applying vacuum would then subject the volumes fore and aft of the bulkheads to a vacuum with catastrophic failure of the unsupported deck.
Bagging a hull requires either a female mold, like fiberglass boat contsruction, or strip building the first layer of the hull and vacuum bagging subsequent layers onto the strip hull. Trying to vaccuum bag the deck would flatten it between the bulkheads and each end of the boat where it is unsupported. A 20" Hg vacuum (~10 psi) over an unsupported area of 12" x 48" exerts an equialent point load of 5760 lbs. Imagine applying a vacuum to an empty milk jug. It would be cheaper to park your car on the deck as clamping force, and probably with the same outcome.
The use of straps and spanish windlasses is the way to go to avoid nails.
In Response to: Vacuum Bagging Decks by Richard Lincoln on Nov 3, 2007
- Re: Vacuum Bagging Decks by theo on Nov 6, 2007