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The Arno XI - A Floating Ferrari?

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The world's only powerboat that can claim factory backed Ferrari power.

There are few people who have travelled at more than 100mph on water, but I am one of them – and it’s terrifying. I was strapped (and trapped) in an Evolution Class powerboat with two 11-liter engines and a hull made from state-of-the-art materials, but the impression was more of being inside a jet-propelled cigar tube skimming over a concrete sea.

As a result, I can only wonder at the mental state of the late Achille Castoldi, leading powerboat racer of the 1940s and ’50s for whom ‘faster’ was never quite fast enough. Having set the 400kg-class World Speed Record in 1940 by piloting his boat Arno to 81.10mph with the help of an Alfa Romeo 158 engine, his quest for ever greater aquatic velocity resulted in no fewer than ten further Arnos, each madder and badder than the last.

The zenith of his obsessive project – Arno XI – you see here. The chances are you’ll recognise its shape, because various modelmakers have immortalised it in miniature. But the real thing has remained out of the public eye for 50 years, together with the remarkable story of its creation.

That dates back to the early 1950s, when the suitably wealthy Castoldi found himself growing tired of the other rich playboys, also demonstrating their prowess on the water at the wheel of hydroplane powerboats propelled by former racing car engines, usually made by Alfa or Maserati. One rival, Mario Verga, proved particularly irksome, having adopted Alfa Romeo power to pursue the 800kg speed record in a boat called Laura.

What Castoldi needed was some serious firepower, something that 
no-one else had thought of using or, indeed, would even be able to get hold of. Something like, for example, a V12 out of a Ferrari Grand Prix car. Castoldi counted among his chums the works Ferrari drivers Alberto Ascari and Luigi Villoresi, who persuaded Enzo Ferrari that it would be 
a very good idea to supply their boat-barmy friend with technical help, and maybe even an engine or two, so he could set some new records.

For the 1953 season, Castoldi commissioned Como-based Cantieri Timossi to build an 800kg-class three-point hydroplane (so called because only the tips of the two hulls and the propellor make contact with the water when the boat is planing), which he would name Arno XI.

It was constructed with a solid wood frame overlaid with a skin of marine ply topped-off with mahogany veneer, plus an aluminium fairing, rear spoiler and engine cover. Motive power came from a Type 375 V12 engine of the sort that, at Silverstone in 1951, had given Ferrari its first Grand Prix victory. Displacing 4.5 liters, it ran twin-plug heads and produced 385 horsepower – sufficient, when transferred through a step-up gearbox, to spin Arno XI’s propellor at a frantic 10,000rpm.

The new rig proved quick and, even during testing at the 1953 Campione d’Italia race, Castoldi touched almost 125mph – but Verga, with the full backing of Alfa Romeo, bested him in Laura during the official two-way run with an average (and class record-breaking) run of 125.68mph which, a fortnight later, he improved. To 140.74mph!

So Castoldi returned to Ferrari, who agreed to supply another 375 engine, this time with twin superchargers, a higher compression ratio and a taste for methanol. Result: more than 500bhp. Enzo Ferrari had the engine set up by chief Scuderia engineer Stefano Meazza and, on 15 October 1953, Castoldi smashed Verga’s record with an average flying kilometer of 150.49mph on Lake Iseo. Still not content, he moved on to a larger, potentially faster Timossi hydroplane powered by an aero engine – but retired in 1954 after surviving potentially fatal mechanical failure.

Arno XI was sold to engineer Nando dell’Orto, who continued to race it successfully for a decade before mothballing it in his paper mill, where it lay dormant for more than 25 years until it was passed on as part of the business to industrialist and Ferrari collector Luciano Mombelli.

Mombelli subjected the boat to a three-year restoration during the 1990s, since when it has been meticulously maintained and occasionally given outings at public events, where the sound of the 375 Compressore Nautico engine has reliably thrilled the crowds.

In May, however, Arno XI will be offered to the highest bidder when it appears as one of the star lots at RM’s Monaco sale, held during the principality’s Grand Prix Historique weekend. Although it carries a reshaped engine cover and front fairing – modifications carried out during dell’Orto’s ownership to improve stability – Arno XI is, in 
essence, just as it was when Castoldi piloted it to more than 150mph all those years ago to set a record which, remarkably, remains unbroken for the class. It will be sold with a fascinating history file that includes period photographs and handwritten notes made by Ferrari engineers during bench testing at Maranello and on the water at Lake Iseo.

‘As the only boat entitled to carry the Ferrari name and to be built with the personal help of Enzo Ferrari himself, it is bound to appeal to any serious enthusiast of the marque who already owns a collection of important Ferrari cars,’ says RM’s Peter Wallman.

‘It has immaculate provenance and has even been immortalised in various scale models which, until now, have been the nearest one could get to actually owning the only official Ferrari boat ever made.’

Arno XI will not, however, be going cheap. Because it is unique and because the values of classic Ferrari cars have reached the stratosphere, RM will offer it with a pre-sale estimate of up to €1.5 million. Unique opportunities cost.

Whoever buys Arno XI will not be able to race it in the way that Castoldi and dell’Orto did: the fearsome reputation of the three-point hydroplanes of the era eventually resulted in the sport being banned. However, the new owner will undoubtedly be invited to perform demonstration runs in the boat at prestigious events around the world. And they will, of course, be entitled to display what could be the ultimate in automotive window stickers: ‘My other Ferrari’s a boat’…

Arno XI was sold by RM Auctions in Monaco on May 11, 2012 for €868,000. For more information about the sale, visit


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