My finale for this thread. This is in FD scale because a 14m vessel in SB would be too bland and undetailed.
The Project 1355 Luftkissenfahrzeug (air cushion vehicle). This was designed and built at Schiffswerft Rechlin and tested between August 1962 to October 1963 so isn't strictly speaking an unbuilt type but was a research vehicle that went no further. How the nose fan was powered is not clear, I doubt the single radial had enough power to drive both the propeller and the fan so there might have been another engine in the nose.
Specifications; displacement 10 tons, 14 m x 3.7 m, powered by one M-11 5-cyl radial engine, 21 knots, 2 crew.