Sixty-foot "Open 60" monohulls emerged in single-handed round-the-world racing in the mid-1980s, notably in the 1986 BOC Challenge. In 1991 a group of leading offshore sailors, including Isabelle Autissier, Christophe Auguin, Alain Gautier and Jean-Luc Van Den Heede, founded the International Monohull Open Class Association (IMOCA) to govern these boats. The France-based class, now headquartered in Lorient, was granted international class status by ISAF (now World Sailing) in 1998.
IMOCA is a development class: its rule sets a framework (length, draught, stability, safety) within which designers and teams are free to innovate. The canting keel arrived in 1998 and soon became standard. From 2013, to contain costs and improve safety, the mast and keel fin became one-design and beam was capped at 5.85 m.
The mid-2010s ushered in the foiling era: six boats fitted with lifting foils started the 2016 Vendée Globe, and later generations (2019-2020, then 2023-2024) pushed partial flight further, with larger foils kept in check by the rule. The 2021-2025 rule cycle capped foil size and extended the list of one-design parts to the boom, keel rams, standing rigging and satellite communications.
The Vendée Globe, the non-stop, unassisted solo race around the world, remains the class's flagship event, alongside the Route du Rhum, the Transat Jacques Vabre and, with full crews, The Ocean Race, which IMOCAs contested for the first time in 2023. A championship, the IMOCA Globe Series, was created in 2018, and Antoine Mermod has chaired the class since 2017.
Since the early 2020s, IMOCA has made the environment central to its development: a lower-impact "Green Sail" became compulsory on board from 2023, and in April 2024 the class adopted an impact reduction rule requiring new boats built between 2025 and 2028 to cut at least 60 tonnes of CO2 against a baseline set by a life-cycle assessment study.
IMOCA is a box rule, not a one-design: boats must fit within maximum dimensions (60-foot hull, about 18.28 m, 5.85 m beam, 4.50 m draught, limited overall length including bowsprit) and meet stability and safety criteria, but designers and builders are free to shape hull, deck and appendages within that box.
Appendages are controlled: two rudders and a canting keel, plus at most two further appendages (foils or daggerboards). For the 2021-2025 cycle, foil area is capped and the number of foils per cycle limited. Several parts are one-design for safety and cost control: mast, boom, keel fin and rams, standing rigging and satellite communications. The number of sails is limited and electronics must come from an approved list.
The rule sets requirements for unsinkability, impact resistance around keel and foils, and renewable energy on board. Its environmental side has grown: a lower-impact sail has been compulsory since 2023, and an impact reduction rule adopted in 2024 requires new boats built in 2025-2028 to emit at least 60 tonnes of CO2 less, measured with the Eco-Score tool.
Boats race solo, double-handed or crewed depending on the event. The rule is written and maintained by the IMOCA class association, recognised by World Sailing.
Source: IMOCA rules (opens in a new tab) (IMOCA)
10 sources · updated 2 Nov 2026
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Source: Sillage, charte graphique : palette des classes (opens in a new tab)
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Source: International Monohull Open Class Association — Wikipédia (opens in a new tab)
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Source: International Monohull Open Class Association — Wikipédia (opens in a new tab)
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Descriptions merged