Designed to break water speed records, it was built between 1952 and 1953 by the Cantiere Timossi boatyard, located in Azzano (a frazione of Mezzegra) on the shores of Lake Como.

[citation needed] Castoldi managed to further increase horsepower by attaching two superchargers.

The result was a 502 bhp speedboat, which he used to hit a 150.19 mph top speed in October 1953 on Lake Iseo.

Like Arno XI, it utilizes a Lampredi engine, in this case sourced from a wrecked Ferrari 375 MM.

[4] Arno XI was later sold and raced in numerous competitions, finally retiring in 1960.