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Denison Debates: Aluminum vs. Fiberglass

August 19, 2015 7:57 am

Both aluminum and fiberglass are reputable materials that have been widely used throughout the boat building industry for many decades. The debate over which material is better depends on a number of factors, including preference. Superyacht broker and owner of Broward Yachts, Christopher “Kit” Denison takes the side of aluminum, while yacht broker, Morgan Bertram defends fiberglass.


Kit Denison: Fiberglass boats are plastic, and given time, salt water can seep into the hull and cause thousands of small blisters all over the boat. It happens all the time, but they don’t talk about it. The repair is expensive and can cost an upwards of $60,000 for a 100-foot boat. Additionally, the osmosis of water into the inner fibers of a fiberglass hull can result in rotting.

Morgan Bertram: Aluminum has a reputation for bubbling and blistering paint finishes. It produces a dimpling effect on the hull. Additionally, aluminum hulls are susceptible to corrosion, particularly in salt water. If aluminum is not properly protected by zinc anodes, electrolysis can occur, which weakens the aluminum and causes deterioration.

Kit’s Rebuttal: There is no “dimpling” or “oil-canning” effect in modern, custom aluminum yachts. The structure of these modern, aluminum yachts provides for the smallest unsupported panel size of any material, including fiberglass. Also, modern, aluminum yachts are protected by a “CAPAC monitoring system,” which prevents the risk of electrolysis and any structural weakening.

Morgan’s Rebuttal: Present day composite technology has limited blistering in fiberglass hulls. Properly constructed hulls using high quality materials, in a clean environment, will prevent blistering and delamination.


Kit Denison: Fiberglass boats are more popular today because there are more of them. It’s like saying there are more Chevy cars than Ferraris; it’s the comparison of a manufactured product with a high performance, high strength product.

Morgan Bertram:  Looking around the industry, it’s no question that fiberglass is the more popular choice. A newer technique, fiberglass has become very popular because it can be molded into any shape. A boat manufacturer can get their money’s worth from a large production of fiberglass hulls.

Custom Features and Design

Kit Denison: There shouldn’t be much of debate in terms of customization because fiberglass requires a mold, which is expensive and has to be perfect to create multiple parts. Aluminum lends itself more easily to being customized, making it the preferred choice of custom builders. The benefit of aluminum is you are hand-building, which allows the owner to make changes during the process, such as extending the length of the boat or modifying the superstructure.

Morgan Bertram: With a fiberglass mold, you can damn the hulls to create more sizes out of the same mold as well as stretch the mold. For production purposes, fiberglass has a clear advantage over aluminum. Customizations for parts, such a fish box instead of a fold down seat aft, is a simple modification with fiberglass because you can put a block in the mold and make the changes.

Kit’s Rebuttal: Actually, aluminum yachts are very easy to customize. A good example is the installation of a live-bait well on the inside of a cockpit.

Weight Capabilities

Kit Denison: Aluminum hulls are not more susceptible to “bouncing” than any other hull, as the hull shape is a made design. In fact, you can build an aluminum yacht to any “high performance” specification; structure is structure, fiberglass or aluminum. Also, aluminum is much lighter. A 70-foot Hatteras weighs more than 100-foot Broward. When you are racing, the goal is to reach the breaking point without actually breaking. With that said, the more high performance and high tech the composite is, the more likely it is to break.

Morgan Bertram: Fiberglass is heavier than aluminum, and it will provide a solid ride with less pounding. A lightweight aluminum boat can feel less grounded during high-speed maneuvers. Fiberglass has the advantage in weight savings for smaller boats. With any racing application, you are going to find composite boats, as seen in high performance sailboats. Any high performance product today would be built of composite. America’s Cup and Racing Offshore Powerboats are good examples; neither has been built of aluminum in over 20 years.

Construction and Cost

Kit Denison: The construction technique with aluminum is much more labor-intensive and requires certified welders. Aluminum production labor is easier to inspect. Building an aluminum yacht completely from scratch is considerably cheaper and faster than building the same yacht out of fiberglass. With fiberglass, you need to create molds, which takes time to develop and requires more man-hours.

Morgan Bertram: You have to build a few more hulls to get the efficiency in fiberglass production, but once you get going, the process is faster than aluminum. As you build more fiberglass hulls, production costs are reduced. You pay for the tooling cost in the beginning and can build more boats faster over time. Fiberglass construction is the obvious choice for production manufacturers.


Kit Denison: Today, in any place in the world, you can find qualified professionals to repair aluminum or aluminum yachts. The real-world experience of yacht repair yards finds no significant difference in the maintenance between aluminum and fiberglass yachts, given equivalent professional crews. Also, there are no riveted aluminum yachts built today; all aluminum yachts are full-welded aluminum construction.

Morgan Bertram: For simple repairs, fiberglass is easier to work with. It’s also easier to find someone to repair fiberglass. Fiberglass requires less hull maintenance because there are no rivets, welds, or corrosion like with aluminum.

Morgan’s Rebuttal: Speaking in general boatbuilding terms, rivets are still used to construct aluminum pontoon boats and canoes.

Stability and Strength

Kit Denison: Aluminum is stronger than fiberglass. If you hit a rock on a fiberglass boat, it will crack or make a hole. An aluminum boat will just get a dent. It will bend, but it won’t break.

Morgan Bertram: Fiberglass is stronger, especially when using materials like Kevlar. There is also more flexibility where you want to put the weight in fiberglass. For instance, you could build lighter parts higher up. The heavier weight of fiberglass provides a more stable ride. Fiberglass allows you to layer up in areas of high stress as well.

Kit’s Rebuttal: Aluminum yachts will typically have lighter superstructures than GRP yachts because aluminum structures can be built lighter and stronger than any other yacht building material. The airplane is the best example of aluminum’s strength. In fact, even on large GRP yachts, you will find structures like a mast or radar arch (at the higher levels) are typically built out of aluminum, not fiberglass.

Morgan’s Rebuttal: On larger yachts, 40 meters and bigger, fiberglass does in fact lose its advantage over aluminum. Using Kevlar and carbon fiber in smaller boats provides greater strength than aluminum. DuPont, the maker of Kevlar, advertises it as being stronger than steel.

Speed, Range, and Ride

Kit Denison: You are going to build a lighter and faster boat with more fuel in aluminum than you would in fiberglass. The whole bottom of the boat is going to be a tank, and with the double-bottom feature of the “integral tankage” of modern aluminum hulls, the result is more fuel capacity per foot. Typically, a 100-foot aluminum yacht will have a tank capacity of 8,000 – 9,000 US gallons; whereas, a composite yacht of that size would typically have a fuel capacity of 4,000 – 5,000 US gallons.

Morgan Bertram: Building with fiberglass below 40 meters gives you a lighter, stronger, and faster boat than aluminum. This will allow for more speed, increased range, and a quieter ride with less maintenance.

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