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Vacuum Resin Infusion Explained

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By Peter Frederiksen

Tracking the flow of resin infusion is easy, just look for the dark areas to see the progress.

This is where closed-mold manufacturing comes into play. The process is resin infusion and it is already in use by leading-edge boatbuilders. Resin infusion, also called vacuum infusion, is the ticket to modern fiberglass boat construction. The show begins with a mold cavity containing the dry fiberglass laminates, as well as Kevlar or carbon fiber if used. The dry laminates are covered with a special bag material, which is then sealed to the mold flange. Flow media is installed that serves as a conduit to direct the resin that will enter the mold via a series of tubes connected to a manifold. A hull is a complex part with a dozen or more lay-up schedules and several different core types, and these factors are taken into consideration because they affect resin flow. 

Accordingly, there can be 20 to 60 or more resin inlets and these are monitored during the process as the resin is pulled through the mold under vacuum. When the valves on the manifold are opened, the catalyzed resin flows freely, wetting the laminates under the bag. There is no sound and no smell as the resin flows through the tubes. However, it is fascinating to watch the laminates turn from white to red as the resin is vacuumed through; it actually resembles blood leaking out from underneath a bandage. In the process, however, there is no waste of resin, but rather a completely predictable amount is used with every job. There are no brushes, no rollers, no splatters. Compared to the familiar mess of open-mold construction, vacuum resin infusion is like a day at the beach. 

An entire 60-foot hull will be infused in a couple of hours, although the actual time to completion varies on the boat’s LOA and other factors. But the end result is a part that offers a 50/50 ratio, 50 percent resin, 50 percent fiberglass, which makes for a stronger, lighter part with a higher fiberglass ratio in comparison to an open-molded part. Although some weight savings will be realized with the resin-infusion process, it is a combination of the weight savings, a cleaner working environment, and reduced emissions that tell the big story. And within hours after the infusion is completed, workers can then begin installing bulkheads and egg crating (a part that stiffens and strenthens via a unity of longitudinal/transverse members) inside the hull moving the process quickly along to the next stage of building the boat’s interior.

A module unit is set in place in the hull.