I could not find the story on
www.proboat.com either but I would guess the depreciation of the gen set would need to be taken into account. For example $10K purchase price divided by 5000 hour lifetime is $2/hr before fuel, or maint costs. If you produce 4Kw per hour, thats $0.50/KwHr for depreciation. Add say 1 GPH fuel use for $4/Hr results in another $1/KwHr. Thats a long way from $19/KwHr.
There must be high maintenance costs added somewhere along the way to drive it up to $19. I guess if you paid marina rates for all maint and did nothing yourself.