i agree about hybrids with a gen set as an interim step.
as i said in my post, i think the amount of solar required to make a difference would be "absurd and impractical". i still do. solar doesnt make sense. i'm not sure why you're on about the solar.
using a quoted number of 1 gallon per hour per 18 horsepower, you should use 8 hp x (1gph/18 hp) = 8/18 = 0.44 gph. you have an 18 gallon fuel tank. you should get 18/0.44 = 41 hours of motoring not 10 days x 24 hours = 240 hours of motoring. as i stated, i think 30 hours of 10 hp motoring is possible with today's technology. not too different.
15 years ago you probably couldnt buy a high resolution GPS colour chartplotter accurate to a few metres for a billion dollars. you can probably still find threads debating celestial navigation versus gps. carbon fiber spars used to be insanely expensive. now there are producion carbon fiber hulls and the boeing 787 (yes, it has its problems). i have lithium ion power drill, lawn mower, weed wacker, LED lights, notebook computer and outboard motor. none of these were around 10 years ago. five years ago you couldnt get a high capacity lithium ion battery. now you can but they're expensive. in five years, probably de rigueur with bigger and better available.
there is a bias in our brains that presumes stasis. change is coming. dont bet against change.