Chapter OneHow Boats Are Built
Why do your own boat maintenance, repairs, and upgrades? There are a lot of good reasons, but the most obvious one is financial. Most maintenance tasks are straightforward and can be done by most boatowners. Rather than spending $70 to $90 per hour for a marine mechanic or technician to do a job, do it yourself and save the bucks. Besides, you'll learn more about your boat, be able to recognize small problems before they become big problems, and be able to fix things in an emergency.
Convenience and personal preference are also good reasons to do it yourself. You may have gotten a good deal on a boat that doesn't have exactly the equipment you wanted and now would like to add. Need more storage for cruising gear? Want to make your boat better suited to fishing by installing rod holders or a T-top? Want to brighten up the interior by adding larger portlights? Tired of raising the anchor by hand and want the mechanical assist of an electric windlass? Learning to do the job yourself is an economical way to upgrade your boat to exactly the configuration you want, with the additions exactly where and how you want them.
Even with the advantages of doing it yourself, it's still reasonable to have a professional do some or all of these jobs for you. In that case, this book is here to give you a sound basis for knowing what is involved and to help you decide if the job is being done right in a realistic time for a realistic price.
This book is organized by the functional areas of a boat, starting with the cockpit and moving on to the galley and the cabin, the decks, the "canvas"-covered areas, and the hull. We make no attempt to cover every possible repair or maintenance project for any of these areas. Rather, the intention of this book is to provide lots of good projects to make your boat safer, more comfortable, and more functional, and to keep it that way. Here and there you'll find sidebars giving additional background or explaining procedures that have broad application to many projects. Following our coverage of the structural components of hull, decks, and cabin, we shift our attention to electrical and electronic projects, the engine and drivetrain, and trailers. Then we end with winterization projects to keep your boat in good shape during the off-season and to minimize the work of recommissioning it in the spring.
You will probably jump right to the section you are most interested in and may not read the entire book. For that reason, you'll find frequent cross-references to tips and techniques that are common to projects in various areas of the boat.
Before we begin the projects, let's take a moment in the balance of Chapter 1 to discuss how boats are built. Unless you know a little about the underlying structures and techniques used in making boats, you will be flying blind when it comes to maintaining or modifying them. Since this book is primarily about small fiberglass powerboats, that's where we'll focus our attention.
Fiberglass boats are built from a composite material known broadly as fiber-reinforced plastic, or FRP. This consists of strands of fibers embedded in a matrix of a hardened plastic resin to form a rigid material that is stronger and has better mechanical properties than either material by itself. Both the fiber strands and the resin can be of several different types.
"Glass-reinforced plastic," or GRP, is a slightly more specific term than FRP, and it can be accurately applied to the majority of boats, because fiberglass is by far the most common reinforcing fiber in FRP. Fiberglass is real glass that has been melted and forced under pressure through fine holes in a die. After exiting the die, the glass fibers can be stretched or blasted with steam or air to make them even finer, and the resultant strands are then coated with a sizing and wound onto bobbins.
Fiberglass for boatbuilding comes in a variety of constructions. Tight bundles of fine strands can be woven into fiberglass cloth, which formerly (but not so much any longer) found frequent use as the finished interior surface of a molded hull or component. It is still used in small boats, where its high tensile and flexural strength works well in conjunction with lightweight mat (as discussed later in this chapter).
Larger bundles of coarser strands can be grouped to form a roving, which looks like untwisted twine. These rovings can be used in chopper guns (described later in this chapter) or woven into a coarse, heavy cloth called woven roving. The fiberglass strands can also be chopped into short lengths and glued into a mat, much like felt. There are other configurations as well, some of which we discuss as they become relevant in later chapters.
Each configuration has different properties and is used in different parts of a boat and in different ways. Most fiberglass boat hulls these days are laid up using alternating layers of mat and woven roving, often beginning with two layers of mat under the exterior gelcoat to prevent the weave of the roving from "printing through" the gelcoat to be visible on the exterior.
In the early decades of composite boatbuilding, glass fiber reinforcements were the only choice. Through the miracles of modern chemistry, however, we now have several additional materials, each with different properties.
Carbon fiber is used in high-performance composite parts. Carbon fibers are three times stronger and four times lighter than steel. They add stiffness as well as strength to properly designed and built laminates. These characteristics can be achieved only with a careful orientation of fibers in the resin matrix.
Prepregs are carbon fiber materials suspended in a partially cured resin matrix (usually epoxy). The prepreg material can be handled, cut, and precisely applied to a mold. The resulting laminate is then cured under heat and pressure to form a completed part.
Kevlar is a DuPont brand name for aramid polymers. Kevlar is widely used in personal body armor as well as reinforcements in boat hulls. Kevlar is five times as strong as steel for a given weight. It requires careful application, as it tends to float on top of wet resin, and it is difficult to sand and fair.
Generally speaking, the higher tech the reinforcing material, the more precise its application needs to be to achieve its highest potential. Naval architects and boatbuilders spend a great deal of time optimizing the exact composition and configuration of hull laminations and reinforcements.
Reinforcements are only half the picture. The other half is the resin, which, in boatbuilding, is either polyester, vinylester, or epoxy. These are applied as a thick liquid that has been catalyzed or mixed with a hardener, either of which turns the resin hard so that it encapsulates the reinforcing materials in a rigid matrix. Generally speaking, the reinforcements contribute tensile strength while the resins contribute stiffness. Together these components are more than the sum of their parts, and they are the basis of modern fiberglass boatbuilding.
Heat affects the cure time of any resin system. The higher the temperature, the faster the cure. These resins are exothermic, meaning that they generate heat while they cure. This becomes a problem if you have a large amount of resin in a container. I have seen epoxy and polyester get dangerously hot and even boil over when too much was mixed and not applied soon enough. By the way, the amount of time the resin remains workable in a pot after mixing is referred to as pot life.
Polyester resin was one of the first resins to be widely used with fiberglass. A small amount of catalyst (typically 1 to 2 percent by volume) is added to trigger polymerization and cause the resin to harden. The resin-to-catalyst ratio is highly dependant on temperature and humidity and should be adjusted accordingly for best results.
The use of polyester resin began with attempts to develop alternatives for aluminum during World War II. After the resin was perfected in the late 1950s, fiberglass boatbuilding exploded. Early fiberglass boats were touted as being impervious to water and maintenance-free. We know better now, but perfecting this resin fueled the conversion of recreational boatbuilding from wood to plastic.
As time has proven, boats built from polyester do sometimes absorb water and develop osmotic blisters. Early resins were less susceptible to the problem, but resin reformulations in the late 1970s and 1980s produced hulls that were more likely to blister. Blistering problems were worsened by less-than-adequate quality control in some of the lamination processes.
Polyester resins usually come with a styrene monomer added to make the resin less viscous and easier to handle, and to aid in hardening. This styrene was the cause of the familiar "polyester" smell in most mold shops in the past. The fumes are now regulated as volatile organic compounds (VOCs), which has forced boatbuilders to add safety and antipollution equipment and develop new molding methods that greatly reduce the pungent odor.
Polyester resin, by itself, is air-inhibited: it won't cure in the presence of air, and the surface will stay tacky. That is a useful characteristic when you are laying up a hull with successive applications of resin and fiberglass reinforcements, because each layer will chemically bond to the next. Such resins are identified as laminating resins.
A wax compound can be added to the resin to create a finishing resin. While curing, the wax migrates to the surface of the resin and seals it from contact with air, allowing the surface to cure hard. (This can also be accomplished by spraying on a mold release compound such as polyvinyl alcohol, or PVA.) Finishing resin is used for the final laminations.
Whether building a new boat or making repairs, it's important to select the right resin. When building up successive laminations, you don't want to use a finishing resin, because the wax will prevent additional layers from adhering and must be sanded off before the next layer can be applied. On the other hand, for a final layer, you do want to use a finishing resin to ensure a complete cure.
The vinylester molecule is chemically similar to polyester but has fewer ester groups. Since ester groups are the resin component most subject to water degradation and osmotic blistering, vinylester resins are more resistant to blistering.
Many boatbuilders now use vinylesters, at least in the outer layers of hull laminations. Boats built with these resins often offer extended hull warranties against blistering. The downside is that vinylester resins cost more than polyester.
Epoxy differs from ester-based resins in that it requires a hardener as opposed to a catalyst. The hardener is added to the epoxy resin in a critical, defined ratio, typically ranging from 5:1 (resin to hardener) to 1:1, depending upon the manufacturer. (In contrast, just a few drops of catalyst suffice to make a pot of polyester resin "kick." Although adding extra catalyst will accelerate the cure of polyester, adding extra hardener to epoxy will not accelerate the cure but will simply weaken the resin structure.)
When mixed and applied correctly, epoxy is much stronger and more water resistant than either of the ester type of resins. Epoxy's water resistance is so good, in fact, that epoxy can be used as a barrier coat over polyester, and this is often done as a repair in cases of extreme blistering. Epoxy is far more costly than the ester resins, however, so it is not often used as the primary resin in composite boats, with the exception of very high-end racing sailboats where light weight is critical and cost is less of an issue.
Since both components in epoxyresin and hardenercompletely react, there are very few VOCs to worry about. Unfortunately, some people become sensitized to epoxy resin and break out in hives or experience other difficulties in the presence of uncured resin. For that reason, gloves, masks, and other protective gear are recommended when using epoxies.
Resin bonds between two composite parts are referred to as primary bonds when there is a chemical reaction between the parts and the resin, so that the two parts become essentially one. A secondary bond exists if the resin simply serves as an adhesive that mechanically connects the two parts. During construction, primary bonds are generally preferable, since they are stronger; but to accomplish this, the construction schedule must be carefully planned so that subsequent parts or laminations go together before the previous ones are fully cured. Bonds between parts in repairs are necessarily secondary bonds, and epoxy should be used whether the substrate is epoxy or polyester, because epoxy forms a much stronger secondary bond with either material.
Epoxy has poor resistance to ultraviolet (UV) rays, and sunlight causes it to break down fairly quickly. All epoxy-coated surfaces that are exposed to sunlight must be protected with paint or with a varnish that contains UV-blocking compounds.
THE MOLDING PROCESS
Fiberglass molds are themselves usually made from fiberglass. A prototype of the part to be molded, called a plug, is built. It can be made from foam, wood, or other temporary materials or can even be an actual hull. In any case, it is the exact shape of the finished part. It is sanded, painted, and polished. The finish of the plug will be the resulting finish of the mold, so great care is taken to get it perfect. It is then waxed and a coat of tooling gelcoat is applied. Tooling gelcoat is usually black or red and is harder, and thus more durable, than regular gelcoat.
Layers of fiberglass are then built up on top of the tooling gelcoat to form the structural basis of the mold. Reinforcements and handling aids are then bonded to the shell of the mold. These handling aids allow the mold to be rocked on its side and moved around the mold shop.
Once the mold is removed from the plug, its interior surfacewhich will be the exterior surface of the hull or other part to be moldedis polished to a fine finish. This finish will be replicated in the molded part, so it must be perfect in every way. After polishing, wax is applied to the mold and buffed several times. This forms the mold release, a finish the fiberglass will not bond to.
Gelcoat is then sprayed into the mold. Gelcoat is a specialized form of polyester resin that forms the shiny exterior surface of the hull or other part being molded and protects the laminations beneath from UV rays. Gelcoat is applied by itself, and needs to be of a uniform thickness, usually 10 to 20 mils. (A mil is one thousandth of an inch0.001 inchso 10 mils is 0.010 inch.) Many boats are gelcoated in a single color, but some boat-builders mask off designs in the mold and spray different colors to create features like bootstripes and covestripes. Great care must be taken to apply the gelcoat in a uniform thickness, especially in corners. A thick web of gelcoat in a corner is likely to chip or crack.
The gelcoat is air-inhibited and remains tacky to the touch. This allows it to bond to the next layer being applied. This layer is composed of short fiberglass fibers and resin. It can be applied either in the form of a mat or with a chopper gun. The mat is composed of short fiberglass strands compressed together with a binder, much like felt. The styrene in the polyester resin dissolves the binder and allows the fiberglass to conform to the curves of the mold.
A chopper gun looks like a spray gun with an attitude. Resin and the catalyst are sprayed from a nozzle. The resin and catalyst mix on their way to the mold. This eliminates any problems with catalyzed resin curing in the gun itself. On top of the gun is an air-driven cutter or chopper. Fiberglass rovingstrands of untwisted fiberglass strands are fed into the chopper. The resultant short strands are also blown into the mold and coated with the now catalyzed resin. Often a red strand is embedded in the roving to give a visual indication of the thickness of the layer being applied.
The mat or the chopper gun layer is then rolled out using grooved rollers. The rollers break up any air bubbles in the mat, compress the strands, and ensure that they are uniformly coated with resin.
After one or two layers of mat are applied, more layers of fiberglass follow. These additional layers are either woven glass cloth or woven roving, often alternating with layers of mat. The outer layer(s) of mat cushions the next layer and prevents "print-through," in which the weave of the cloth or roving is visible in the final finish. When layers of mat alternate with layers of woven roving, the mat fills in the roving's coarse weave and creates a better bond for successive layers of roving.
Most production boats have a defined lamination schedule, spelling out the size and placement of the reinforcing material. Often these are precut and arrive at the mold ready to place. This schedule is designed to make sure the proper amounts of reinforcements are placed in the right locations in the mold.
Following the initial fabric layers, sections of core are applied (as described later in this chapter). Again, most of the core is precut and is applied in precise locations in the mold. The final, interior skin of fiberglass is then built up on top of the core. This forms the inside, or rough side, of the molded part.
Early in the fiberglass boatbuilding evolution, it was realized that stronger and lighter structures could be made by utilizing a "sandwich" or "cored" technique. A lightweight center core is placed between two layers of fiberglass. The resulting structure is lighter than the equivalent solid fiberglass structure but thicker and much, much stiffer.