There were the Russian Cazar's round ships with lenticular hulls...
Quote:
https://en.wikipedia.org › wiki › Russian_monitor_Novgorod
Russian monitor Novgorod - Wikipedia
Novgorod ( Russian: Новгород) was a monitor built for the Imperial Russian Navy in the 1870s. She was one of the most unusual warships ever constructed, and still survives in popular naval myth as one of the worst warships ever built.
https://www.19fortyfive.com › 2021 › 06 › russias-circular-battleship-was-one-strange-warship-and-a-joke
Russia's Circular Battleship Was One Strange Warship (And a Joke)
27 Jun 2021If the battle didn't come to the round monitor, the round monitor was unlikely to make it in time for a battle. However, Czar Alexander II apparently still liked the design enough that when Popov proposed a round Imperial yacht the Emperor agreed! Called the "Livadia," it was assembled in England and transported to Sevastopol for a sea trial.
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..but carry it forward and you get the Sea Orbiter
www.seaorbiter.com
Technically a small-waterline mono-hull.