Hand laid boats are laminated by forcing resin into fiberglass cloth manually, usually with a roller or a brush. The wet fiberglass is then smoothed out to eliminate as much air from the laminate as possible. Certain types of fiberglass are used in this method that lend themselves to ease of lamination. Such materials include Chopped Strand Mat (short strands of random oriented fiberglass) and woven fiberglass. While easy to manipulate on a mold by hand, these materials absorb large amounts of resin, and have inferior orientation to distribute loads across a part.
Because the resin is catalyzed, there is a limited amount of time allowed to complete this process before the resin hardens and the fiberglass can no longer be smoothed. Also, the quality of the final laminate is completely at the mercy of the skill of the laminator, so different boats made by different laminators can vary significantly in strength and weight.
Resin infusion, on the other hand, is done by using a vacuum pump to draw resin through fiberglass that’s being compressed against a mold. The laminate is first carefully applied to the mold, and can be continuously checked for accuracy without any time constraint. Because the laminate will ultimately be compressed by vacuum, more technical fabrics can be utilized that would otherwise be difficult or impossible to lay up by hand.
Once the team is satisfied that all of the correct layers are in place, a bag is sealed over the entire mold, and the entire piece is compressed under vacuum. The resin only takes 5-10 minutes to be drawn through the entire boat, which eliminates any time stress. The resulting laminate is incredibly consistent from part to part.
Aside from being a more consistent and accurate method of lamination, resin infusion also results in laminate with improved mechanical properties. For demonstration purposes, the following graphs outline mechanical properties of three different types of 18 oz fiberglass. The woven roving is a typical fiberglass used for hand lamination and the E-LT 1800 are used in hand layup as well, but can be difficult to work when the individual strands are enlarged for strength. The final laminate is an infused E-LT 1800.
With these charts you can see that there is an inverse relationship between the resin content in a laminate and its ultimate strength. If we use the color red as an indicator of resin content, we can look again at the images of infused and hand laid laminates. The more intense the shade of red, the higher the resin content, which means a weaker laminate.
Ultimately, this all boils down to one simple statement. A resin infused laminate used in a boat will be more consistent, lighter, and stronger.