Fiberglass Boat Repairs Illustrated - Softcover

Marshall, Roger

Softcover

ISBN 10: 0071549927 ISBN 13: 9780071549929

Publisher: International Marine/Ragged Mountain Press, 2010

Synopsis

Step-by-step color photo guidance forrepairing and renewing fiberglass boats

If you don't have the experience of working withfiberglass, any repairs to your boat must be done by high-costprofessionals or left undone. This entry-level guide usesfull-color, step-by-step photo sequences and line drawingsto present you with the basics in an easily digested form. You will learn how to:

• Save money and time doing your own fiberglassrepairs
• Improve the value, appearance, and safety of yourboat
• Work with materials such as polyester, epoxy, fiberglass,carbon fiber, and core materials
• Fix annoying leaks; repair cracks; restore gelcoat;fabricate new components

About this title

About the Author

Roger Marshall is an accomplished yachtdesigner, competitive sailor, and author of 12 yachting books.After designing for the renowned firm of Sparkman &Stephens, he established his own design company, where hehas designed sailboats and powerboats from 15 to 65 feet.Project manager in 1987 for the Courageous America’s Cupteam, he has written some 600 articles for boating magazinesworldwide and is chair of the publications committee for theSociety of Naval Architects and Marine Engineers.

Excerpt. © Reprinted by permission. All rights reserved.

Fiberglass Boat Repairs Illustrated

By Roger Marshall

The McGraw-Hill Companies, Inc.

Copyright © 2010 Roger Marshall
All right reserved.
ISBN: 978-0-07-154992-9

Contents

Chapter One

HOW FIBERGLASS BOATS ARE BUILT

Before you can begin repairing or rebuilding a fiberglass boat, you need to understand how it is put together. Such knowledge will also tell you when a contemplated repair job is worth the time and money, and when it is likely to be so difficult or costly that you'd be better served to give up on the boat.

Consider, for example, a boat with a foam-cored hull that has been holed in a collision. You need to determine how to get to the back of the hole. This usually means cutting away the damaged section of the outer fiberglass skin, or laminate, pulling out the core around the hole, repairing or replacing the inner fiberglass skin, filling the area with new core material, and finally replacing the outer laminate. If you are not familiar with fiberglass composite construction, you could spend more time than the boat is worth just trying to get it apart.

This chapter's aim is to avoid such problems by familiarizing you with the materials and methods of fiberglass boat construction. Entire books have been written on this subject. Though this chapter is only an overview, it will provide sufficient background for the repairs a boatowner or small shop is likely to do.

FIBERGLASS HULLS

Just as a cotton sheet drapes over a mattress, a sheet of fiberglass material conforms to the shape of any object into which or over which it is draped. Only when resin is added to the fiberglass and allowed to cure does the fiberglass shape become fixed. But what does fiberglass get draped over or into to create the shape of a hull or any of the other parts that go into the construction of a boat? The answer, of course, is a mold.

A mold can be either female or male. The finished part fits inside a female mold or over the outside of a male mold, the choice depending upon whether the inside or outside surface of the part is intended to be the smooth, finished surface. Since the outside surface of a hull is the one we present to the world and want to have mirror-smooth, a fiberglass hull is usually laminated in a female mold. Most boats built today also have a smooth interior liner, which fits into the hull somewhat like a garbage bag fits inside a kitchen trash can, and into which the cabin or cockpit furniture is molded. This part, also known as a pan (see the Hull Liners section on page 22), is made in a separate fiberglass mold.

Fiberglass revolutionized boating in the post-war years by enabling multiple copies of a hull to be produced one after the other from a single mold. Since the mold has a highly polished interior surface, the hull comes out of the mold with smooth topsides that are then polished mirror-smooth. While the hull is still in the mold, its interior reinforcements and structures are installed. Its deck and its furniture and fittings are added as the boat moves down the production line. A successful fiberglass boat enjoys a production run of dozens, hundreds, or in a few cases even thousands of copies, depending on the boat's size and popularity.

Building a Mold

Clearly the hull mold is critical to the appearance and integrity of the finished hull. The method of building a hull mold has evolved over the decades of fiberglass boatbuilding, but the fundamentals have remained unchanged. The builder must first create a male plug of the same size and shape as the finished hull and then shape the female mold over that plug. The mold is then reinforced on the outside, removed from the plug, and polished on the inside to prepare it for the production run. Building a plug and a mold and all the other smaller parts for a production run may cost as much as or more than building a single boat. The builder hopes to amortize the cost of the plug and mold over the production run of the model.

When a fiberglass boat is built on a custom, or one-off, basis, the plug and mold represent costly items that are used once only to be thrown away. To avoid the need for a mold, custom fiberglass builders almost always laminate the hull over a male plug or forms. This necessitates laborious fairing and polishing of the hull's exterior surface, however. Alternatively, a one-off large powerboat may be made in a female mold that is built from plywood and does not require building a plug. Fiberglass is laid up inside the mold and polished to a high sheen, and the boat's hull is then laminated in this.

Almost all production runs begin with both a plug and a mold, however. The photos that follow show the building of the plug and mold for one of my designs, the 24-foot Avid powerboat. Construction details vary from one mold to the next, but this one is representative.

Molds for decks, cockpit tubs, and smaller parts are made in the same way, although usually most of the inside of a mold is reachable without having to use a ladder or staging as is needed with a hull mold. Complex shapes, such as a steering console, may be constructed in two- or three-part molds designed to allow the piece to be removed easily when formed.

Forming a Hull in a Mold

Having made a plug and a female mold, a boatbuilder's next step is to laminate the first hull in the mold—hull #1 of what the builder hopes will be a long and successful production run. We'll discuss solid-fiberglass hulls first, and then look at how the laminate schedule is modified to build a hull cored with balsa, foam, or some other material.

Solid, Single-Skin Fiberglass Construction

Solid, single-skin fiberglass construction is the original method of fiberglass boat construction, and it's still in use. First, gelcoat is sprayed to a more-or-less uniform thickness against the mold's mirror-smooth polished interior surface and allowed to set up. The gelcoat might be anywhere from 5 to 20 mils thick (a mil is a thousandth of an inch) but is usually at least 10 mils thick and more often 15 to 20, making it an order of magnitude thicker than a coat of paint. Unlike a coat of paint, it is also chemically cross- linked (not just mechanically adhered) to the fiberglass laminate that follows it into the mold. When the hull is later lifted out of its mold, the gelcoat becomes the laminate's outer coating and serves to protect the hull from UV degradation, scratches, and minor dings. It is not only beautiful but also highly durable.

Through the first three decades of fiberglass boatbuilding, gelcoats were almost universally a pigmented polyester resin. But polyester has the drawback of allowing moisture to penetrate the gelcoat via osmosis and attack the structural laminate beneath it. This can cause blistering (see Chapters 2 and 8), and after blistering began to show up in boat hulls beginning in the late 1980s, most production builders began using a vinylester (a vinyl-based polyester) gelcoat in lieu of the traditional polyester gelcoat—or an epoxy barrier coat over a traditional polyester gelcoat—thus curtailing moisture penetration. Some builders—generally those building high-performance boats—now use vinylester or epoxy throughout the hull laminate, not just in the gelcoat, but this is rare in production boatbuilding.

The gelcoat is usually followed by one or more commonly two layers of chopped strand mat (CSM). Mat consists of short strands that are packed together in random orientations to form a flat sheet, then held together with a binder that is resin- soluble. CSM is more easily molded than any other fiberglass material. For this reason—and because it prevents the pattern of the woven fiberglass materials beneath it from printing through, or showing on the hull surface—it is the obvious choice to comprise the first one or two layers of laminate behind the gelcoat. The common weights of CSM are 3/4 ounce and 1½ ounces per square foot.

In production boatbuilding, some manufacturers apply CSM not in sheets but with a chopper gun, a tool that chops continuous strands of fiberglass into predetermined lengths and fires them into the mold along with a fine spray of resin. The idea is that the fiberglass is coated with resin on its way into the mold. Chopper guns were commonly used ten years ago because they make the initial laminating go faster, but they are less commonly used now because they emit large quantities of volatile organic carbons (VOCs) and can produce uneven results in the hands of an unskilled operator. You should not need a chopper gun for repair work.

On top of the CSM (i.e., beneath it in the finished hull), builders usually place the first layer of woven fiberglass reinforcement. The usual choice for this among commercial builders is woven roving, which consists of thick bundles, or rovings, of parallel strands, with the warp and weft rovings crossing each other at 90 degrees. The result is a heavy, coarse weave that builds up laminate thickness fast, which is why builders favor it. The most common weights are 18 and 24 ounces per square yard. (Note that all fiberglass materials except CSM are weighed by the square yard, not the square foot.)

Woven roving provides great strength in the warp and weft directions but is not as strong along the bias. To address this, successive layers of roving in a laminate can be oriented at 45 degrees from one another. Also, adjacent layers of woven roving do not bond well enough for boatbuilding purposes, so a typical laminate schedule alternates layers of roving with layers of CSM, which provides superior interlaminar bonding. Early fiberglass builders aimed for a laminate comprising about 30% fiberglass reinforcement and 70% resin, but builders today can get more than 40% glass in a hand-laid laminate, and even more if using vacuum bagging or resin-infusion techniques. (For more on vacuum bagging and resin infusion, see the sidebar on pages 15–17.)

In fiberglass cloth, as in woven roving, the warp and weft fibers cross each other at 90 degrees, but cloth is woven from yarns (each yarn comprising two or more strands of glass twisted together) rather than stout rovings, and the material is therefore neater, easier to work, and more finely woven. Cloth is available in weights from 2 to 20 ounces per square yard, with weights between 6 and 11 ounces being most common and most versatile. Cloth is stronger for its weight than woven roving and makes a neater repair, so although boatbuilders don't use it much in their laminate schedules, it serves well for repairs. In fact, 1½-ounce mat and some 6- to 10-ounce cloth may be all you'll ever need for fiberglass repairs, though 18- to 24-ounce woven roving is also good to have on hand. (Remember, mat is weighed by the square foot, so 1½-ounce mat weighs the same per given coverage as 13½-ounce cloth.)

The thickness of a 30-foot solid fiberglass hull (i.e., one without a core) might range from 1/8 inch (3 mm) at the toerail to ½ inch (12 mm) or more at the keel. Three layers of woven roving separated and sandwiched by five layers of CSM mightyield a finished thickness of 5/16 inch (8 mm). The builder typically lays dry sheets of woven roving into the mold, then wets it with resin in place, working the resin into the weave with squeegees and rollers. (These tools are described in Chapter 3.) This hand layup of roving layers may be alternated with chopper-gun layers of CSM.

As an alternative to hand layup, sheets of resin-impregnated roving or mat—chilled to prevent the premature completion of curing—can be laid into the mold without additional resin. After being laid down, these prepregs are cured by heating, vacuum bagging, or autoclaving. (For more on vacuum bagging and autoclaving, see the sidebar on pages 15–17.)

The resin used in fiberglass building was invariably polyester until the late 1980s, and polyester remains the predominant choice today. As mentioned, however, since osmotic blisters were found to be a problem on older boats, most builders have switched from polyester to vinylester gelcoat or an epoxy external barrier coat. Some use vinylester throughout the laminate, but vinylester is more expensive than polyester, so others switch to polyester after the gelcoat is in place.

Polyester products are comprised of the resin, a catalyst, and an accelerator. Usually the accelerator comes premixed with the resin (which has the consistency of maple syrup), and a few drops of the catalyst are added as needed. (The catalyst is methyl ethyl ketone peroxide, or MEKP, which is nasty stuff and not something you want in contact with your skin.) Mixing the two components initiates an exothermic reaction, and heat is given off as the catalyzed resin sets up into a solid, never to be liquefied again. Because heat is emitted in curing, polyester resins are known as thermosetting resins, and the laminating process must proceed a couple of layers at a time, since the simultaneous curing of more layers than that might produce enough heat to damage or warp the mold and, in a worst case, even start a fire.

Like polyester resins, epoxy laminating resins come in two parts—the resin and a hardener—that need to be mixed before they will cure. Performance craft are built almost exclusively with epoxy resins because the resulting laminate is stronger and stiffer. Few production boats are built with epoxy resin—which is much more expensive than polyester—but that doesn't mean you can't use epoxy for repairs. I prefer epoxy for many repairs, in fact, as discussed in Chapter 3 and elsewhere in this book.

Cored Construction

Single-skin, solid fiberglass hulls were universal among early fiberglass boats, but balsa- cored decks and a lesser number of balsa-cored hulls were being built by the 1970s, and other core materials followed. Cored, or sandwich, construction is in most respects the same as single-skin construction, except that the builder inserts a layer of lighter material midway through the layup, separating the laminate into inner and outer skins. This makes the hull or deck thicker, and therefore much stiffer, without adding much weight. It also insulates against heat and sound and reduces condensation in the boat's interior.

The builder must ensure a good bond of the core material to the outer and inner skins. This is critical. Delamination of a core-skin bond is difficult for a do-it-yourselfer to repair.

Through-hulls, deck hardware, and other laminate-penetrating items should not be mounted on or through a cored laminate without proper precautions. To ignore this warning is to invite moisture through the outer skin and into the core along hardware fasteners, and this will sooner or later cause a balsa core to rot and a foam core to become waterlogged and spongy. Further, even when hardware is through-bolted with adequate backing plates, cinching up on the nuts can crush a balsa or foam core and form an indent in the deck, perhaps cracking the laminate. A good builder will make a transition from a cored deck to a solid laminate for a hardware installation, at a deck edge, or for the tightly radiused curve from deck to cabin side. Most experts now agree that the core taper through the transition to solid laminate should be about 3:1—i.e., if the core is 1 inch (25 mm) thick, the taper to a single skin should be 3 inches (75 mm) long. This allows the single skin to flex slightly and transition the load to the cored section, whereas an abrupt change in material stiffness might fracture under load.

If you install a through-hull (for a transducer, a toilet outlet, etc.) in a cored hull, you should cut the hole oversize, remove the core, replace the core with thickened epoxy, and cut a hole of the proper size through the epoxy. Use the same approach for fastener holes in a cored deck. This is covered in detail in Chapter 5 on page 95.

HULL REINFORCEMENTS

Once a hull is laminated, the builder customarily adds interior reinforcements—floors, longitudinals, and bulkheads—to stiffen the hull before removing it from the mold. The common practice prior to the early 1970s was to bond wooden floors, stringers (i.e., longitudinals), and bulkheads to the hull using fiberglass tabbing, fillet joints of thickened resin, or both. Tabbing consists of laying strips of fiberglass cloth over the joint between the hull and covering the reinforcing member with polyester resin. Fillet joints dispense with the fiberglass cloth and instead use thickened resin to accomplish the same thing. (Fillet joints today use thickened epoxy rather than thickened polyester, as covered in Chapter 5 on page 97.) These wooden parts were prone to rot after a few years, and their removal and replacement with foam-cored fiberglass floors is Project #2 in Chapter 7.

(Continues...)

Excerpted from Fiberglass Boat Repairs Illustratedby Roger Marshall Copyright © 2010 by Roger Marshall. Excerpted by permission of The McGraw-Hill Companies, Inc.. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Edition details

• Publisher: International Marine/Ragged Mountain Press
• Publication date: 2010
• Language: English
• ISBN 10: 0071549927
• ISBN 13: 9780071549929
• Binding: Paperback
• Edition number: 1
• Number of pages: 192