Next, resin inpregnated woven mat is layered on and again rolled and depending on the construction alternated with chopped fibers and woven mat until the "lay-up" is finished. This process while simple in theory must be done thoroughly or voids (areas where the gelcoat and mat are not chemically bonded) will be left. Next the whole works is rolled along it's entire surface to insure a good bond between the two. This operation is accomplished with what is called a chopper gun which mixes the fiberglass mat and polyester resin in the proper proportions. Next a layer of chopped, stranded glass mixed with polyester resin is shot into the mold completely covering the gelcoat layer, again evenly. With the mold prepared, the gelcoat is sprayed over the entire surface of the mold to a uniform thickness. In modern fiberglass boat building a new boat is "layed up" (built) in a female mold which has been polished smooth and waxed with a specially formulated release wax to allow the finished boat to be removed. One of our complaints about Taiwan boats has always been that they make use of the chopper gun too much. And for other uses where very high strength is not required. A very thin layer of mat is also used between heavy fabrics to prevent concentrations of resin between the heavy fabrics. Chopped strand mat (CSM) is still used on all boats to prevent the weave pattern of fabrics like roving from showing on the gel coat surface. That does not mean that chopped strand mat and chopper guns have disappeared from boat shops. For this reason, chopped strand is not considered as a structural fiber. Today, things like shower stalls, truck fenders and the Corvette automobile body are made with chopper guns because they don't require great strength like a boat hull. The chopper-gun boats soon disappeared from the scene. Those "blow-molded" boats tended to break up all to soon. Very quickly we learned just how weak laminates made with short fibers are. The length of these fibers was about 3-4 inches and were usually curled like cut hair when viewed in the mold. In the early years of small FRP boat building, a few companies tried making boats from chopped strands of fibers, mixed with polyester resin and blown through a gun into a mold. You can also see the fibergalss mat being laid the entire length of the boat. It is all matting and roughly 3/8" to 1/2" thick. You can see this if you have ever cut out a chunk of your BU. Today, there is a large variety of weaves available, but they are all essentially weaves of continuous fibers. These fibers, much like the huge cables that hold up suspension bridges, rely upon the continuous lengths and orientation of the fibers for their strength. The length of some of these woven fibers run the length of the boat. The fiberglass consists of fabrics of woven mat made of continuous fibers. It consists of a basic standard of 65% continuous glass fibers, in the form of fabrics, and 35% plastic resin. This is the full name of what, for over forty years, has been known as the fiberglass boat. Hand laid fiberglass boats (such as Malibu) are also referred to as Fiberglass Reinforced Plastic (FRP) boats. Here is some interesting information that I found that discusses the difference between Hand laid boats, chopper boats, layed up boats and cored hull boats.
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