Thought this was cool and I'd pass it on.
I stumbled across these guys www.megoutboard.com who are in the pre-production stage of a line of turbo diesel outboards in the 175, 225 and 300HP ranges.
Their 3.0L (300hp) weighs 723lbs and their 2.3L tested out at on a 22 foot CC Glassmaster @ 39.6mph WOT burning 6 GPH, which works out to 6.6 MPG.
I emailed them volunteering to be a motor tester and this is what they sent back:
Thank you for your interest in Maritime Engineering Group's Vision Turbo Diesel Outboard. The outboards that we will be producing will be in the initial range of 115hp-230hp and will meet all emission standards. When we get closer to our production date pricing will be available. The weight of our engines will be similar to other 4 stroke outboards and for durability our engine will also have closed cooling.
Below are a couple videos to show our new prototype during testing.
Due to the economy we are about 6 to 9 months away from our production to start and the first units are all ready spoken for by a few branches of the military so true production units to the public are about 12 months away.