Ouch....

OK...manufacturing methods for producing a catamaran (or anything) from a female mold can fall into two basic categories. Hand Laid or Vacuum Bagged. "Foam Core" is about having foam between layers of fiberglass and you can build a boat with foam core construction using either method.

Hand laid hulls are exactly that. Gelcoat is sprayed in the mold and allowed to tack up. Precut pieces of fiberglass are laid on top of the gel coat and wetted out with resin. Then a foam core is placed on top of the wet fiberglass. Then more fiberglass on top of the foam core is laid in place and impregnated with resin.

For a simple vacuum bag operation, the same previous processes would take place. After all this glass is 'wet' a perforated layer of plastic goes on top of it all, then a layer of absorbant stuffing sheet (usually poly-stuffing), and finally the vacuum bag. A small port is installed in the bag and vacuum applied. As the air is evacuated from inside the bag, the ambient air pressure starts pressing equally around the mold and squeezes excess resin from the laminate through the perforated plastic layer into the stuffing. You end up with a laminate with less resin, less weight, and more fiber density resulting in a potentially stronger part.

Resin infusion simply takes vacuum bagging to a new level. You still spray the gelcoat in the mold but you lay in the fiberglass, core, and reinforcements in the mold dry. You don't put in the perforated plastic layer or the stuffing - only the vacuum bag. You pull a vacuum on the dry layup and once the bag is well sealed (and you've chased all the leaks), you connect an open pail of resin to the center of the bag in several places (where ports have been pre-arranged) and let it start to suck the resin in. The resin will slowly work it's way through the laminate. Once one area of the mold is fully impregnated with resin, you clamp off that port while the rest of the mold infuses. Resin infusion uses less materials (no more perforated layer or stuffing), you have more time to lay the materials in and get them right, and you get a very controlable amount of resin in the layup. The drawbacks are that the port and flow arrangement is very critical to get resin in all the nooks and crannies, the curing time of the resin (affected largely by ambient and mold temperature) is very critical (you don't need it to start gelling before everything is infused!), and the (low) viscosity of the resin is super-critical.