Cylinder Molding And Vacuum Bagging

[zstine]

I'm confused about how the laminate, a plywood layup, can be "vacuum formed" to the mold when "plastic [bagging] sheet is laid over the mold first and then sealed around the assembled [plywood laminate] sheets."

My understanding is the mold is just ribs and a few stringers to hold them up, not an airtight mold as is typical of mass produced boats. If you wrap your lamination on both sides/all around with a vacuum bag, vice having the mold as one of the sides holding vacuum, how can this 'suck' your lamination down to the mold?

What am I missing? Seems to me the mold either has to be airtight to be used for vacuum forming the ply laminate or the whole mold needs to be 'in the bag'.

reference:
https://multihulldesigns.com/pdf/cm/...NSTRUCTION.htm

https://smalltridesign.com/Trimaran-...struction.html

[psk125]

The first link you post mentions a "bagging table", and/or using the substrate ply layer as the "bagging table":

"I do notice that they never count the time to build a bagging table in the time-to-build. In CM, the panel is its own bagging table, as it were. One is not needed."

After gaps have been filled in with "bog", even the first layer of a multi-ply hull IS airtight, and can serve as a base for vacuum bagging. Both the Cylinder-Moulded and Constant Camber methods use this approach. WoodenBoat has had several articles on vacuum bagging that describe the step by step procedures which would clarify the process for you.