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Engineer and speedboat racer Nando Dell’Orto races the Arno XI with his #50 painted on the hull.

Engineer and speedboat racer Nando Dell’Orto races the Arno XI with his #50 painted on the hull.

A one-off Ferrari Formula One engine modified for hydroplane racing lives on—almost 70 years after breaking the world speed record on water.

It was a clear, calm October morning on Lake Iseo in Italy in 1953. Soon, the glassy water on the fourth-largest lake in Lombardy would transform into a speedway for the fastest waterborne vessels in the world. For Achille Castoldi, this morning was one of great anticipation and uncertainty that was three years in the making. As he sat in the cockpit of his 800-kilogram (1,763-pound) hydroplane, he had no idea what was in store. He only hoped the Arno XI and its 350-hp Ferrari Formula One engine would be fast—really fast.

Hydroplane race boats arrived in Europe from the Americas in the early 20th century. Originally designed with a hull step located amidships, the boats skimmed over the water, offering superior speed to the original speedboats that plowed through the water. These vessels could run in just about any conditions imaginable, from large rivers and lakes to salt water. However, they could be difficult to handle, described as riding much like a bucking horse.

The original Ferrari F1 engine that powered the Arno XI to 150+ mph in 1953 is still in the boat today, a testament to its engineering.

The original Ferrari F1 engine that powered the Arno XI to 150+ mph in 1953 is still in the boat today, a testament to its engineering.

In the late 1930s, the three-point hydroplane emerged, which would make a permanent impact on the world of powerboat racing. On these vessels, which were first imagined by Ventnor Boat Works in New Jersey, the step was split into two sponsons placed on opposite sides of the hull to create a pontoon-like running surface that was wider and less likely to tip over than the original hydroplane. Three-point hydroplanes trapped air in the tunnel between the sponsons, which added lift, reduced friction, and resulted in greater speeds. While unable to perform in rough water like their single-step predecessors, they could achieve spectacular feats on small, protected bodies of water. In the years following World War II, when converted aircraft and other power sources became readily available, hydroplane racing took off as a sport.

Castoldi was no stranger to speedboat racing, having competed for more than a decade on various craft powered by Alfa Romeo engines. His first race boat, named Arno, was a 400-kg hydroplane with an Alfa Romeo Type 158 engine that broke the speed record for the class at 81.1 mph. He also broke the speed record for the 450-kg class with the Arno II. But this wasn’t satisfactory for the sportsman, who was set on one mission: to break the world speed record on water for the 800-kg class. Sir Malcolm Campbell set the record in 1939, achieving a speed of 141.74 mph. To break this record, Castoldi would need the most advanced engine possible. So, he turned to one of the biggest names in motor racing and engine design, Enzo Ferrari.

The Ferrari name was still relatively new to Formula One racing in the early 1950s, but the company had already cemented itself as a serious player. After its 1950 Grand Prix debut in Monaco, it secured its first victory at the British Grand Prix in 1951, formally establishing itself as one of the leading innovators in motorsports.

After setting his sights on breaking the record in 1950, Castoldi traveled with Ferrari Grand Prix drivers Alberto Ascari and Luigi Villoresito to the Ferrari headquarters in Maranello, Italy, in 1951. There, he met Enzo Ferrari and made a lofty pitch. Castoldi wished to use an F1 level racing engine in his hydroplane race boat. Ferrari had only built four such engines at the time, but after hearing Castoldi’s plan to put Ferrari technology on the water, Enzo Ferrari not only agreed to give him an engine, but volunteered to be personally involved in every step of the project. Now, Ferrari would have three engines devoted to F1 auto racing and one engine devoted to speedboat racing.

A crowd looks excitedly at the Arno XI, which beat the world speed record for the 800-kg hydroplane class, a record that still stands today.

A crowd looks excitedly at the Arno XI, which beat the world speed record for the 800-kg hydroplane class, a record that still stands today.

The first step in the project was building a racing hydroplane boat that could support the F1 engine. They commissioned Carlo Timossi for the job, who had started his career by developing specialized hydroplanes at the famous Pietro Riva yard on Lake Iseo before partnering with champion pilot Ezio Selva to create a series of hydroplanes called Moschettiere, which were powered by Alfa Romeo F1 engines.

In 1952, Timossi completed the 800-kg class hydroplane for Castoldi, which was built from steel and wood with a mahogany finish. The boat was named Arno XI and stamped as Hull 001. Yet the most important element was still to come: the power. Ferrari may have been one of the most advanced engine builders of the era, but it had never powered a waterborne vessel. Enzo Ferrari rallied the top minds at the company to turn an F1 engine into a one-of-a-kind speedboat engine, including Chief Engineer Auerrio Lampredi and Chief Race Engineer Stefano Meazza.

The team at Ferrari decided to outfit the Arno XI with a 4.5-liter Type 375 12-cylinder engine—the same engine found under the hood of the first Ferrari 375 race car to win an F1 event. Ferrari made unique modifications so the engine would be suitable for the water. The result was unlike any engine ever built.

Achille Castoldi with the Arno XI, which sports his #4

Achille Castoldi with the Arno XI, which sports his #4

With a 12:1 compression, the engine drove 10,000 rpm to a twin-blade propeller. The dual-magneto ignition system featured 24 spark plugs, rather than the usual 12. The magnetos, which were used in place of distributor caps, would ensure that the engine would keep running even if soaked in water.

This engine produced 350 bhp, and test runs in early 1953 revealed that it could propel the hydroplane to speeds topping 100 mph. But this wasn’t fast enough for Castoldi or Ferrari. So, they modified the engine for methanol fuel, which would allow higher compression ratios, and added two root compressors and a pair of four-choke carburetors. With these modifications, the engine could deliver more than 500 bhp. After the Ferrari team finessed the hydroplane’s weight distribution and balance with this massive engine, painted the exterior in Italian racing red, and christened the boat with Castoldi’s #4, it was time to put the beast to the test.

Nobody could predict how the Arno XI would perform on October 15, or if the vessel would even remain intact with such a powertrain. But when Castoldi pressed the throttle down, history was made. He dominated the 800-kg class with a two-way average speed of 150.19 mph, setting a new record. He followed that run by setting another record in the 24-nautical-mile event. A year later, Castoldi would retire from racing at the top of his career. His record still stands to this day.

The boat demonstrates the superior lift of three-point hydroplanes that allowed them to achieve great speeds in protected waters.

The boat demonstrates the superior lift of three-point hydroplanes that allowed them to achieve great speeds in protected waters.

The Arno XI switched hands three times after Castoldi’s historic victory. It was purchased in 1958 by wealthy engineer and speedboat racer Nando Dell’Orto, who modified the body lines on the engine cover and the fairing with a “shark nose” intake, and added a vertical stabilizing fin aft. Perhaps most notably, he replaced Castoldi’s #4 with his own #50. He went on to set several fastest-lap records in circuit championships around Europe and claimed victory at the 1963 European Championship before retiring the boat from competition in 1968. By the time the boat retired, the original Ferrari engine had been propelling it to speeds topping 100 mph for 17 years.

The Arno XI then moved to a warehouse in the south of Milan, where it remained untouched for 25 years before being purchased in the early 1990s by Ferrari collector Luciano Mombelli, who was determined to restore the vessel to her original glory. He launched a full factory restoration of the original engine at Ferrari Classiche, where the engineers rebuilt the overhead camshafts, replaced the valves, and reconditioned the four-choke carburetors. During the restoration, the twin superchargers produced an astonishing 600-plus bhp during a bench test, and the Arno XI was also converted to run on high-octane unleaded fuel rather than methanol. Meanwhile, the hull was restored by the Bisoli boatyard in Northern Italy, which constructed a new deck for the vessel. Once the restoration was complete, the Arno XI took to the water once again in 2004, where it received praise from Enzo’s son, Piero Ferrari.

In 2012, the Arno XI was sold again, this time to a businessman and philanthropist based in Austin, Texas, who is now determined to share this legendary vessel with the world and keep its legacy alive.

“I’ve been a Ferrari enthusiast and collector since the late 70s or early 80s,” he says, explaining that he currently has a car collection of 35 vehicles, which includes Ferraris, Porches and McLarens, and at one time owned more than 100 cars. “This was an opportunity to own something so unique, and I couldn’t pass it up.”

The owner grew up on the Gulf of Mexico in Texas and has owned many speedboats throughout his life, including a 55-foot Fountain, a couple of Velocity speedboats, and a Paradigm ski boat that he recently purchased to use on the lake where he lives in central Texas. He also owns a boat from Eastern Europe that was used to pick up astronauts returning to Earth from a space expedition. “I like things that are unique and different,” he says.

After the new owner purchased the Arno XI, Ferrari contacted him directly to ask about displaying the vessel at the Enzo Ferrari Museum in Modena and the Ferrari Museum in Maranello. The owner agreed. The vessel was displayed side-by-side with the 1951 Ferrari F1 winner, and hundreds of thousands of Ferrari enthusiasts from around the globe visited it while it was on loan until 2019.

The owner also conducted a complete engine rebuild on the vessel at Ferrari Classiche in 2019 to ensure it was in top shape ahead of its 70th anniversary. “Ferrari Classiche will restore any Ferrari vehicle back to new condition,” he explains. There, the Ferrari technicians worked by hand on the same engine that Enzo Ferrari personally helped design. They also added a custom running stand to display the boat on land as well as the water. According to the owner, this historic hydroplane has likely lived out its racing days. “Because of the uniqueness, it would be difficult to find parts to rebuild if necessary,” he explains.

Nevertheless, the Arno XI has a busy agenda moving forward, with the owner planning on displaying it at the Thailand Yacht Show and Monaco Yacht Show in 2022, with a possible appearance in Dubai in between.

“This boat is such an important part of Ferrari’s history. Ferrari’s first win was in 1951, the boat was being built in 1952 and Ferrari’s first World Cup win was in 1952. This engine was part of that ascent,” he says. “I feel very fortunate to own a piece of this racing history. It’s one of one; there will never be another like it.”

This article originally appeared in the June/July 2022 issue of Power & Motoryacht magazine.