Magnetohydrodynamic drives (MHDD) use the Lorentz force to propel watercraft through seawater without moving parts. The Yamato-1, launched in 1992, was the only full-scale prototype to carry humans, using liquid helium-cooled superconducting coils to accelerate seawater ions. Despite its innovative design, the system achieved only 15% efficiency and a top speed of 8 knots due to seawater's limited conductivity. The prototype was scrapped in 2016, and MHDDs remain impractical for mainstream marine propulsion.
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