Curiosity got me looking into this. Basic specs on the "boat" can be found at Wikipedia,
LARC-LX - Wikipedia, the free encyclopedia.
The engines may be an upgrade from the original as I crawled around the web I came up with HP ratings between 235 (normal aspiration) and 450 (marinized turbo). The marinized turbo variant is the 6-71 TI. Based on the wikipedia listing the originals were 8 cylinder engines but the yachtworld listing indicates the 6 cylinder engines.
Top speed on land is 15 mph, in the water it is 7.5 mph. After a long search I dug up some rough
fuel consumption for the engine, it is 3.83gph at 1500rpm (motor is rated for peak HP at 2500). Taking a conservative estimate of 4 gph at top rpm and full load you would be burning 16 gph across the 4 motors. With diesel prices north of $4 and heading to $5 this boat would take about $80/hour to run.
I think I will stick with the wind until the government taxes that!