One relatively unexplored direction in human-powered boats is the hydrofoil, in which the hull rides atop aircraft-style wings beneath the water.  Above a certain speed, the entire hull is lifted above the water, reducing drag to almost nothing, and permitting very high speed.  Foilkayak created the Flyak around this idea.

[youtube=http://www.youtube.com/watch?v=U95UReP4mdo&hl=en&fs=1]