According to Shane Kearns, who operates a water taxi in Australia, "Over the 35 engine hours clocked so far I have nearly halved my fuel bill with the twin F350 outboards returning a combined 31 liters per hour across a range of harbor conditions and boat loads. I originally thought my fuel gauges were wrong until I started closely monitoring my fuel intake." When first built, his boat featured twin two-stroke engines, which were later replaced with Yamaha four-stroke outboards. His latest F350s not only reduce fuel consumption but also provide additional speed and power, things which don't normally go together.
[Sources: Yamaha and Gizmag]