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This is a chemical reaction that cannot be undone. Unlike thermoforming plastics like polythene and PVC that can be melted after they set and recast like metal, thermosetting plastics like polyester, vinylester, and epoxy become permanently solid after setting. Applying heat softens them a bit and greatly weakens them indeed, they have very low heat resistance compared to most metals , and they may be set on fire, but they cannot melt and become fluid again.
The glass fibers come in rolls of fabric. The most common sort is electrical-grade glass, known as E-glass, which was originally developed for use in electrical circuit boards. The alternative is structural-grade glass, called S-glass, which was developed for use in airplane construction. S-glass not surprisingly is a much better structural material than E-glass. It is nearly half again as stiff and has much better impact resistance.
Unfortunately, it also costs three times as much, which is why most boats are built of inferior E-glass. Quality builders often use limited amounts of S-glass to reinforce certain heavily loaded areas of a hull or deck, but only rarely do you see an entire boat built out of it.
To make something as large as a boat out of liquid resin and floppy fabric, you need a mold to shape and support the materials until they solidify. In both cases, multiple layers of fabric are built up into a laminate, and after the resin in all the layers has set up hard and cured, the now solid part can be separated from the mold.
When working with a male mold you are building up laminate from the inside out; the outermost layer goes on last, and if you want the outside of your boat to look nice and shiny you must fair and polish the exterior surface afterward. With a female mold, the outermost layer goes on first. Either way you must take the trouble to fair and polish the entire surface at least once. But with a female mold you need do it only once though some intermediate cleaning and polishing is required and can then pop multiple fair-skinned boats from the mold thereafter.
This is why production builders always use female molds. They also use gelcoat, a thin coat of resin thickened with colored pigment, as the very first layer in the laminate so boats emerge from their molds prepainted as well as prefaired. One advantage of fiberglass construction is that it facilitates the creation of complex hull shapes. But some shapes are still easier to form than others. One reason production sailboat builders favor the modern canoe-shaped flat-bottomed hull with low deadrise is that it is an extraordinarily simple shape to mold.
You do have to bolt on a keel afterward, but that is a relatively simple matter of drilling holes and installing fasteners. A classic full-keel shape with lots of deadrise and deep bilges, by comparison, is more problematic since it is often impossible to extract a deep, narrow keel from a one-part mold, no matter how carefully the mold is waxed beforehand.
To ensure success a two-piece mold is often used, so the molded part can be more easily released by separating the halves of the mold. It is also difficult to properly lay up and wet out fiberglass fabric in a deep mold with hard-to-access spaces. In other cases, with tumblehome hulls, for example i. Molds themselves, of course, must also be created.
To build one fiberglass boat, it is often said, you must in fact build two boats: the finished product and the mold from which it springs. With a female mold, you normally build three boats to get one--first a male plug on which the female mold is formed, then the mold, and finally the boat itself. Capital costs, therefore, are quite high, which is why truly custom one-off fiberglass boats are quite rare. It is possible to build fiberglass boats cost-effectively, but only if many boats are born of the same mold.
This is what is unique about fiberglass construction. As late as the middle of the 20th century, boats were always built one at a time. Since the advent of fiberglass, however, boatbuilding has increasingly become an industrial process as opposed to a craft. The biggest builders these days can churn out hundreds--or even thousands--of boats a year on massive assembly lines studded with computer-controlled robots that do everything from spraying gelcoat into molds, to cutting hatches and drilling holes for fasteners in decks, to cutting, trimming, and even varnishing interior woodwork.
But even on the most automated production line, a lot of manual labor is still needed for a boat to be built properly. Given the relatively small market for new sailboats, there is also a surprisingly large number of small builders who still build only limited numbers of boats using little automated machinery. For many in the industry boatbuilding is primarily a labor of love; to them boatbuilding will always be an avocation and never just a business.
Generally, however, the companies with the best long-term chances of survival are those that focus on economic reality and production efficiency. One thing many mass-production builders have come to realize is that their biggest competition is not other builders of new boats, but the ever-growing number of older glass boats that are still on the water. It is now 60 years or so since the first glass boats appeared on the market, and there is still no evidence of any inherent limit to their useful life spans.
As far as we know, a well-built, carefully maintained glass boat can last virtually indefinitely. This, unfortunately, only encourages builders to produce boats that are less than durable. Buyers who expect to trade in or sell a new boat within a few years need not worry about this, as serious maintenance issues are unlikely to arise in the first few years of ownership.
To help those who find their cruising sailboats on the brokerage market i. Having a good basic knowledge of construction techniques can save you from making some big blunders when you buy a boat, so I encourage you to stay tuned. Search Advanced Search. Personal Watercraft for Sale View All. Liked it? Share it! Facebook Twitter. With over two decades of experience in marine journalism, Lenny Rudow has contributed to publications including YachtWorld, boats.
Boat Reviews. Basic Navigation Steve Colgate. Boating Guides. Boat Buyer's Guide. Boat Seller's Guide. Spring Commissioning for Your Boat. Popular Articles Related Articles 1. Five Affordable Trawlers Under 40 Feet. What Hull Shape is Best? Best Boat Brands. What Type is Right for You? Top 10 Choices for Boaters. Fiberglass Repair, Epoxy, Resin, and Help. Dinghy Construction. A Basic Boat Box.
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