[Someone]

The huge speed difference with a single scull probably has more to do with inefficiencies in 'the drive train' (moving your weight around in a rowing shell introduces dipping, which loses energy; using oars is less efficient than using a propeller) than with inefficiencies of the rowing motion vs a cycling motion.

http://rowingbike.com/site/EN/ shows a bike operated using a rowing motion. That machine is competitive with 'normal' recumbent bikes, except in climbs. The main parts also could be fitted on that Decavitator. I would expect similar speeds.

[pge]

Interesting point - it may be that rowing is comparable to biking in power, but the ease of building a cycling drivetrain generally wins out for projects like this, because the parts are readily available in any bike store (the cockpit of the copter here is an off-the-shelf bike frame and crankset attached to the spools).