Arno XI

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{{Infobox ship begin |infobox caption= |display title= none }} {{Infobox ship image |Ship image= Ferrari Arno XI 001.jpg |Ship image size= |Ship caption= Arno XI on display in the Museo Enzo Ferrari }} {{Infobox ship career |Hide header= yes |Ship country= |Ship flag= |Ship name= Arno XI |Ship namesake= Arno |Ship owner= |Ship operator= |Ship ordered= |Ship builder= Cantieri Timossi |Ship original cost= |Ship laid down= |Ship launched= |Ship sponsor= |Ship christened= |Ship completed= |Ship acquired= |Ship commissioned= |Ship recommissioned= |Ship decommissioned= |Ship maiden voyage= |Ship in service= |Ship out of service= |Ship renamed= |Ship nickname= |Ship fate= |Ship status= |Ship notes= }} {{Infobox ship characteristics |Hide header= |Header caption= |Ship class= |Ship type= Hydroplane |Ship tonnage= |Ship displacement= |Ship length= {{convert|6200|mm|ftin|1|abbr=on}} |Ship beam= {{convert|2470|mm|ftin|1|abbr=on}} |Ship height= |Ship draught= |Ship depth= |Ship power= 1× 4,493.73 cc Ferrari Lampredi V12 with twin superchargers and twin four-choke carburettors; 600+ bhp |Ship propulsion= |Ship speed= |Ship range= |Ship endurance= |Ship notes= }}

Arno XI is a hydroplane conceived by {{ill|Achille Castoldi|it}}. 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. Castoldi persuaded Ferrari, via its racing drivers Alberto Ascari and Luigi Villoresi, to supply him with the same power unit used in the Ferrari 375 F1.{{cite web|last=Nichol |first=Mark |url=http://uk.autoblog.com/2012/02/20/amazing-1m-vintage-ferrari-speedboat-for-sale/ |title=Amazing £1m vintage Ferrari speedboat for sale - Autoblog UK |publisher=Uk.autoblog.com |date=2012-02-20 |accessdate=2012-05-25}}{{cite web|url=http://www.sportscardigest.com/ferrari-hydroplane-offered-at-rm-auctions-monaco-2012/ |title=Ferrari Hydroplane Offered at RM Auctions Monaco 2012 |publisher=Sportscardigest.com |date= |accessdate=2012-05-25}}

The engine was installed in a Timossi three-point racing hydroplane hull.{{citation needed|date=June 2023}} 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. This world speed record for an 800 kg boat still stands today.{{cite web|url=http://www.gizmag.com/ferrari-racing-boat-auction/21546/ |title=World record-winning Ferrari racing boat to go on the auction block this spring |publisher=New Atlas |date=2012-02-21 |accessdate=2012-05-25}}

A similar hydroplane was constructed by Guido Monzino in 1954. Like Arno XI, it utilizes a Lampredi engine, in this case sourced from a wrecked Ferrari 375 MM.{{cite web | last=Guétat | first=Gérald | title=Heart Transplant | website=Forza Magazine | date=28 August 2014 | url=https://www.forza-mag.com/issues/137/articles/heart-transplant | access-date=2 June 2023}}