Bauxite. It’s not an ore most folks think about very often, and it’s not very exciting when it comes out of the Earth as it’s just, well, a boring, dull-colored rock. But smelt it and mix it with other metals and bauxite turns into a fabulous boatbuilding material: aluminum. It’s strong, light, corrosion-resistant, easy to work and simple to maintain. Until the fiberglass revolution that began in the 1950s, aluminum was the material of choice for folks wanting a durable, long-lasting yacht without the tyranny of maintaining a wooden vessel. Today, aluminum is making a comeback, as more boatbuilders and their customers recognize the benefits of this versatile metal.

FIRST, SOME HISTORY

Back in the 1950s and 1960s, the country experienced a boating boom like no other and the demand for new boats was strong. At the time, the subject of fiberglass boats versus wooden vessels was very hot. Fiberglass, the new material on the scene, was heavilty touted by builders and marketers as it was stronger, easier to maintain, wouldn’t rot and didn’t need painting. All you had to do was wax it every year and it would shine forever. Before long, fiberglass became so dominant in the recreational boat market that many shoppers never considered buying a craft made of any other material. It was the dawn of the Age of Fiberglass.

Fiberglass transformed the boating industry, in large part because it allowed builders to produce easy-to-maintain, user-friendly boats that were appealing to newcomers in the sport. And builders were able to manufacture fiberglass craft quickly and cost-efficiently, once the tooling—female molds—for the individual components was constructed. Workers could lay up fiberglass and resin in molds much faster than carpenters and welders could build wood or metal hulls.

This is still the prime advantage that fiberglass has over other boatbuilding materials today, including aluminum, although high-tech glass laminates and processes like vacuum-bagging have made building in fiberglass more complex and expensive than it was back in the days of open molds and polyester resins.

As the Age of Fiberglass dawned, sales of aluminum boats declined, but the metal never went away. Builders turned out thousands of riveted-aluminum models, including pontoons, canoes, jon boats and skiffs. They were all boats that even kids at summer camp couldn’t destroy, and neither could fishermen casting into shallow, rock-strewn waters since the occasional bump didn’t bother aluminum plate. Custom sailboats and power boats were frequently built of welded aluminum, mostly because fiberglass doesn’t lend itself to custom work. Some of the top racing sailboats in the 1960s and ’70s were custom-built of aluminum, including the 12-meter Courageous that defended the America’s Cup in 1974 and ’77. Boats that earned their living—commercial rigs—were often built of aluminum, and sometimes steel, to stand up to the abuse that these vessels typically endured. Builders chose aluminum even if it cost more than steel, because it required less maintenance, since it didn’t rust. Paint? Unnecessary.

Those attributes hold true for aluminum today, and that’s one reason why the material has maintained its appeal with builders and boaters over the decades. And there is another benefit: Aluminum can take a hit. Consider the Lewis-Clark Valley near Clarkson, Washington. It’s called the Welded Aluminum Boat Capital of the World, with more than a dozen local boat shops comprising the Snake River Boat Builders consortium. Boating on the rivers in these parts is an obstacle course of shallows, rapids, snags and water-soaked logs. People here ride on aluminum hulls because obstacles in the water won’t damage the material as it might a fiberglass boat or even steel, which is much stiffer than aluminum and doesn’t deform to absorb an impact. The aluminum alloy hull often comes away with just a dent that can be banged out back at the yard. Power a shallow-draft aluminum hull with a jet drive, and you’ve got a boat that will take you just about anywhere there’s water and come back in one piece.

Metal for Marina Queens

But let’s be honest: Most pleasure-boat owners don’t go around running into snags or skipping over shallow-water boulders, and they don’t need the strength and durability of a welded-aluminum boat. Some never venture far from their marina, or the nearest sandbar for swimming. So, what advantages does aluminum have for folks who use their boats for day cruising in comfortable coastal conditions, or even as Marina Queens?

First, aluminum is easier to take care of. There’s no waxing, no compounding, no polishing, no gelcoat crazing. It won’t fade over time from UV rays. Aluminum boats are either painted or, sometimes, powder-coated. Neither finish demands much maintenance beyond regular cleaning to keep the salt and grime off. Skippers who don’t mind the military/commercial look often leave the aluminum bare above the waterline, letting it gradually turn grey as a layer of protective aluminum oxide forms. Leaving the boat au naturel will also save money—the grinding, filling and fairing necessary to create a yacht finish is time-consuming and expensive. Fiberglass has the edge here: It comes out of the mold nice and shiny, but keeping it that way demands regular waxing.

Aluminum is much more abrasion-resistant than gelcoat-covered fiberglass, so if a docking goes awry or a crew misses with the fender chances are the damage will be slight. (In addition, rubrails made of extruded aluminum are more effective at fending off than the hard rubber rails found on fiberglass boats.) Aluminum tenders, RIBs and skiffs can be beached without harm, other than maybe losing a little antifouling, which is easily touched up. If the boat gets scratched through the paint or the oxide layer to bare metal, leave it alone and soon the aluminum will react with oxygen in the air to heal itself. Unlike steel, bare aluminum won’t continue to corrode, so it can be repainted at leisure. With fiberglass, if a scratch or ding penetrates through the gelcoat, water can seep into the laminate, eventually causing more damage, especially if it freezes.

Speaking of water, aluminum boats have no osmosis issues since there is no coring to get wet and cause expensive problems. Most fiberglass boats have cored decks, and topsides are often cored too. Coring lets the builder use less fiberglass while achieving the required stiffness without adding too much weight. Powerboat transoms are cored for the same reason. Inevitably, as the boat ages water will find its way into the coring, turning it to mush if it’s wood and eventually causing delamination no matter what the core material. Repairing wet core is expensive. There is no fear of this with aluminum. There’s structure under the plating to stiffen the material, and nowhere for water to seep in and hide.

Another benefit of aluminum: It can be repaired easily, and the repair will be as good as new: Just cut out the damage and weld in a new plate. Welding the 5000-series alloys used in boatbuilding today causes minimal loss of strength, and a skilled tech will arrange the repair to keep the welds in less-stressed areas, or supported by underlying structure. The new metal will bond securely to the old. That’s not always the case with fiberglass repairs, which can delaminate if not expertly done with the correct resins and surface prep. With aluminum, there’s no fiddling with ersatz molds or backing materials to form the repair into the correct shape. The plate is shaped by machinery in the repair shop (it does take skill to do this) and then welded into place.

Whether done during repairs, modifications or initial construction, the welds that hold an aluminum boat together can be examined and detected. A bad weld can be repaired on the spot. The aluminum can be sampled too, to ensure it’s the proper alloy. The 5000-series alloys used by most boat builders contain up to 4.5 percent magnesium by weight, although the amount varies among the different alloys. The foundry producing the aluminum ensures the mix of metals is correct, and the builder double-checks the balance with techniques that can also be employed when surveying an aluminum boat. That removes any guesswork and allow the surveyor to make a more informed appraisal of the vessel’s condition.

Aluminum Options

If you’re searching for an aluminum boat, it helps to know that there are eight series of aluminum alloys, numbered 1000 to 8000, but only two—5000 and 6000—are used for boatbuilding. Magnesium is the primary alloying metal in the 5000 series: alloys 5052, 5083 and 5086 each contain a few percent, by weight, of magnesium, along with smaller amounts of chromium, silicon and manganese. The 6000 alloys contain less magnesium and more silicon. All the alloys are roughly 95 percent aluminum by weight; other metals make up only a small amount of the alloy.

Most structural components of an aluminum vessel are built with 5000 series alloys. Both 5083 and 5086 are strong and corrosion-resistant, and retain most of their strength when welded, which makes them ideal for hull plating and framing. They can be used to build entire vessels if money isn’t an object (think ships for the Navy or Coast Guard, since these alloys are expensive). Alloy 5052 is less hurtful to the bank account, not quite as strong but more ductile than 5083/86. It can be bent further without cracking, so it’s often used in larger vessels for decks, cabin sides and tops, fuel and water tanks, and places where the plate has to be bent or shaped. Builders of small boats sometimes use it for hulls, too, where ultimate strength versus scantlings isn’t critical.

Alloy 6061 is the primary 6000 alloy used in boatbuilding. It’s most often found in aluminum rails, hardtop frames, arches, sailboat masts, booms and so forth. Unlike the 5000 alloys, 6061, while initially very strong, loses up to half its strength when welded, so it’s used where weld strength isn’t critical. Sometimes 6061 is used for structural components (deck beams, for example), but aluminum boats are mostly built of 5000-series alloys.

LONG LIFE

If you’re looking for one more good reason to add an aluminum hull to your fleet, here’s one: The material can be recycled and then used to build even more boats. Recycled aluminum is as good as new, and many “new” aluminum boats are built with recycled metal. Fiberglass can be recycled, too, but the process isn’t easy. Discarded fiberglass is often ground into powder and used in a variety of industries—as filler for asphalt, for instance. It’s ironic that fiberglass resin, made from petroleum, which we’re supposed to be conserving, isn’t recycled, but ends up effectively on the trash heap, while aluminum, made from bauxite, one of the world’s most abundant ores, can be given a second life.

All of this leads me to conclude that bauxite is really not so boring after all. And it makes a darned nice boat.

This article was originally published in the November 2024 issue.