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Why Fiberglass Boats Sometimes Fail

By badriance - Published October 07, 2009 - Viewed 17878 times

A Primer on Fiberglass Boat Construction


Several years ago, a man pulled into the parking lot at BoatU.S. headquarters trailering a large boat -- a “high performance” boat -- that looked like it had dropped off of the trailer and bounced along the highway. The man wasn’t stopping at BoatU.S. to buy zincs of stove alcohol at the marine center; his mission ultimately was to get a new boat from the manufacturer. Neatly stenciled on the side of the hull, next to a graphic of a large lemon, were “It did not hit anything” and “Under normal operation this boat BROKE APART AND SANK.” The boat was a rolling testament to his ire ... and a boat manufacturer’s worst nightmare.


Caroline Ajootian, who heads up the Consumer Protection Bureau at BoatU.S., remembers that day well.  She remembers the man told her his boat had been badly damaged -- entire sections of fiberglass had been torn away from the hull -- “by hitting a few waves one afternoon.”


Are some boats “lemons”? Here’s a daunting statistic: In an earlier study of why boats sink in open water, six percent failed because their hulls split apart. One well-documented reason that hulls split is because reckless boat owners slam into wakes and waves at high speeds. Another reason, according to Dave Gerr, a naval architect in New York City, is the boats themselves. Gerr, who has written several books on boatbuilding, blames stiff competition among boat builders, “A designer used to be able to tell the front office what would or wouldn’t work, but that doesn’t happen anymore. The last word in building a boat goes to the people who sell the boats.”


Gerr notes that most boat builders do an excellent job. He cites as an example a sailboat manufacturer on the West Coast that builds boats that are both strong and lightweight. The key, he says, is quality control. Another naval architect, Mike Kaufman in Annapolis, Maryland, who also works as a marine surveyor, notes that boats today, though lighter, tend to be built better than the heavier boats that were the norm in years past. He says that there have been improvements in most systems, including fuel tanks, thru-hulls, wiring, and most importantly, the quality of the lay-up. The latter has to do with how resin is applied to the fiberglass to build a hull. In the early years of fiberglass boat building, a lot of mistakes were made because builders didn’t know any better. These days, Kaufman says, failures are more likely to be the result of poor quality control.


Bruce Pfund, a well-regarded consultant on composite fiberglass construction from Rhode Island agrees that quality control can be a problem, but he has also found that some builders deliberately use cheaper materials and take shortcuts in an effort to save money. So while boats may look alike -- shiny with lots of bright chrome -- below the surface there can be significant differences.


A Primer on Fiberglass Boat Construction


To understand why fiberglass components can sometimes fail, you have to understand something about how a fiberglass boat is built. With the typical production boat, building techniques haven’t changed much since the early days of fiberglass: a mold is used to build up layers of chopped strand mat and woven roving that are bonded together with polyester resin. How many layers are used depends on a boat’s scantlings -- the dimensions of its structural parts. A boat with heavy scantlings is said to be better able to cope with heavy stresses -- weather and seas.


Polyester resin, the most basic type of resin, remains the most widely used for boat building. It’s easy to work with, inexpensive and reasonably strong. More recently, vinylester resin has been used by some boat builders to prevent blistering below the waterline. Vinylester laminates are typically tougher and more resilient than polyester and can be used with polyester application equipment. Epoxy resins are tougher still, more resilient, and are even more resistant to blistering. They are not, however, compatible with gel coats -- the shiny surface finishes -- and cost roughly four times as much as polyester. Epoxy tends to be used only on more costly custom boats (typically built for racing) and in special situations.





Water penetrated the plywood core on the transom of this fiberglass boat via a trasnducer fitting that was added by the boat's owner. whenever a hole is drilled through a core below the waterline, it should be tightly sealed with an epoxy paste and then caulked to prevent water penetration. Considering what's at stake, it's one job that is best left to a skilled professional.







One of the most crucial jobs in boat-building is the even distribution of resin over the various layers (plies) of fiberglass cloth to form a solid bond that is free of voids and puddles.  The plies, collectively referred to as the laminate, are typically made of woven roving -- long strands of glass fibers woven together -- and alternate layers of fiberglass mat -- short strands of glass fibers randomly bound in a thin “blanket” that absorbs resin. Because it is made up of longer fibers, woven roving is much stronger than the chopped-strand mat. The latter is used to absorb resin and bind the various layers of woven roving together. Without the mat, woven roving would be filled with un-reinforced puddles of resin.


You might think that gooping a lot of resin would make the various plies stronger, but in fact the opposite is true. Puddles of resin mean a weaker laminate. According to Dave Gerr, “the sole way to get a strong, light laminate is to use just enough resin to get a thorough wet-out and a good bond -- not one whit more. The more fiberglass used in proportion to the resin, the stronger the laminate.” This sounds easier than it is. Applying too little resin means the laminate will be “resin starved,” which is a condition that can cause the various plies to separate. Pfund adds that resin starvation is easier for manufacturers to spot, so excess resin tends to be a more common manufacturing problem.


There are several techniques to aid in matting resin with glass. The least expensive is to use a chopper gun to spray a combination of chopped glass fibers and resin into a mold. This method is quick and inexpensive. The drawback is that chopper gun construction is imprecise and can result in thicker, heavier hulls (which translates into reduced performance). Since the proportion of resin to glass fiber is high, and since the glass fibers are short, chopper gun hulls, though heavy, are not especially strong.


The industry standard, the one used by most boat builders, is to apply resins the way it was done in the earliest days of fiberglass -- using a spray gun. To build a strong hull, just the right amount of resin needs to be sprayed evenly over the layers of glass fiber cloth with no bare of thick spots. In the hands of an experienced employee, the resulting laminate will be sounds and relatively light.


Another technique, one that is used to build light and strong hulls, is vacuum bagging. With this technique, resin-impregnated wet laminates are covered with a plastic film, which is then sealed to the edges of the mold. Using a vacuum pump, air is sucked out, compressing the resin onto the laminate and removing any excess resin. Although it isn’t foolproof, the result of vacuum bagging can be less resin in proportion to glass fiber than is typically found in laminates sprayed by hand.


By itself, a fiberglass hull will be flexible, so bulkheads, stringers, and interiors are added later to give it rigidity. These are “tabbed” to the inside of the hull with several layers of fiberglass. Adding wet layers of laminate over previously cured dry layers is called secondary bonding, a mechanical bond that is not as strong as the primary bond. The latter is a chemical bond that results when layers are added while they are still wet.


If tabbing isn’t done correctly, a slightly weaker secondary bond could become even weaker. Whatever is being tabbed to the primary laminate for structural support, typically wood or foam, must be tapered to eliminate sharp angles. Sharp angles are not as strong as tapered angles. This is also true of adding cores, typically foam or balsa, which are used on most boats to make decks stiffer and to reduce weight up high. Cores are sometimes used in the hull, more often above the waterline, for the same reason -- to reduce weight and add stiffness. Plywood cores, which are stronger and heavier than cores made with balsa or foam, are used in areas that must accommodate a lot of weight or compressive loads, such as transoms on outboard powerboats.


Whenever a wood core or stringer is added, it must be well soaked with several applications of resin before the laminates are added. A single application of resin would be absorbed into the wood, with little or no resin remaining to be absorbed by the glass cloth. Core material, either balsa or foam, has notches and grooves called “kerfs” to accommodate compound curves in the boat’s deck and hull. To maximize strength as well as to prevent water from filling the voids, the kerfs should be filled with resin or putty before the laminate is applied.


Note that if stringers, bulkheads, cores, and interiors are not sufficiently strong to stiffen the hull, or if they fail (i.e. the fiberglass bond breaks or separates), tiny cracks will develop in the flexing laminate. The tendency will be for these to deepen, which can ultimately lead to a catastrophic failure of the laminate.


Poking Around Your Boat: Looking for Telltale Signs of Future Problems


Several years ago, Mike Kaufman invested a considerable amount of money in a device that would gauge the thickness of the fiberglass in a used boat. He was surprised that most of his clients could not have cared less. For the average boat owner, who lacks a degree in naval architecture, the thickness of the laminate in various areas means very little. So how can a boat owner know if a boat is going to wind up looking like the boat with the lemon painted on the side.


A boat’s weight, relative to other boats the same size and type, can give you a clue. So too can the quality of its hardware and finishing work. But with any boat, now or used, the best guide is a manufacturer’s reputation. According to Caroline Ajootian of BoatU.S. Consumer Affairs, price is not necessarily an indication of quality. Some high-volume builders, for example, build consistently sound hulls at a reasonable price. They’re also good with warranty repairs. Other builders, even builders of expensive boats, can hide shoddy fiberglass work behind expensive cabinetry. If you’re not familiar with a manufacturer, ask your surveyor and do some research online. The Coast Guard’s Recall information can be found at BoatAmerica.org/Recall. You can also contact ConsumerAffairs@Boatus.com to learn about problems that have been reported by other BoatU.S. Members. And finally, the BoatU.S. website includes a Boater-to-Boater Directory that allows you to ask over 1100 boat owners about specific make and model boats.


If you already own a boat, the best defense against any unpleasant surprise is to spend time occasionally examining its structure. (Some boat owners hire a marine surveyor periodically to get a more professional examination.) Any problems, if noticed early, can usually be corrected before expensive damage occurs.


First, examine the bonds at bulkheads, stringers, engine beds, and any other parts that add support to the hull. Look for deep cracks that presage separation. Look also for spiderweb cracks on the outside of the hull. Superficial cracks are fairly common and may only be in the gel coat, but longer, deeper cracks at the stringers, bow, and transom could mean trouble. Discoloration at woodwork is a sign of leaks that need to be corrected. Soft spots in the deck are also a strong indication of water penetration. You can “hear” delamination and other fiberglass problems as well as wood rot by tapping various areas with a plastic hammer. Tapping over a wide area gives you a good sense of how a healthy fiberglass or wood surface is supposed to sound. A sharp -- thwack, thwack -- sound is good. A duller -- thump, thump -- may be bad. It’s important to note, however, that built-in tanks, core terminations, and core density can affect sound. Should you have any doubts, contact a marine surveyor or repairer.


If you boat is still under warranty and insured with a BoatU.S. Marine Insurance Yacht Policy, “Investigative Services” will send a surveyor to inspect the damage and write a report that can then be submitted to the manufacturer


A Primer on Laminate Problems: What to Look For



Thin, shallow cracks in the gel coat are fairly common and usually don't indicate anything more than a cosmetic problem. Deeper, wider cracks, however, that run in long lines along the chines ,stringers, or bulkheads may be indicating a more serious problem. Cracks at the stern or keel, and transom are especially worrisome; these areas are supposed to be heavily built and should not be prone to cracking.









This is a good example of stress cracks that are indicating a laminate failure. Dye was used to highlight a series of deep stress cracks at the bow. Further aft the hull laminates have already begun to separate. A naval architect who investigated the damage said the problem appeared to have been caused by a combination of hard use and a weak hull.











Here we see what can happen when water seeps into the core, typically at a fitting. Unlike the builder of this boat, some builder remove the core at areas surrounding thru-hulls below the waterline and build up the plies of fiberglass. Since the fitting is then installed through solid fiberglass, any leaking water will seep into the boat and not the core.




















The owner of this boat noticed water seeping through the bolts used to secure the hatch. An investigation by the boatyard found the screw holes had not been well bedded. Steve D'Antonio, who manages the boatyard that did the repairs, said he's seen tiny snap fasterers do thousands of dollars in damage to a deck because they weren't caulked properly.


Ideally, before a deck is recaulked, screw holes should be drilled out and filled with a thickened epoxy paste so that a leak can't penetrate to the core.


















This photo shows a section of deck above a stanchion that bas been leaking and letting water penetrate into the core (a wood block). In this case, the caulk used to keep water out of the screw holes had, over time, dried and cracked. Water then seeped into the core, froze, expanded and lifted the fiberglass deck off of the core.






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