Last spring a _Popular Mechanics_ type article proposed hyperbaric supercharging of small engines as an alternative to hybrids. When power was needed to scoot across an intersection the boost kicks in and the engine shifts to high power density.
It would be better to do the same thing except backwards:
Start off with a large conventional energy density engine and then convert it to a low power, low power density, low pressure ratio recuperated high efficiency engine when on the highway.
Instead of trying to retool a motor vehicle plant start off with a vessel engine which is more or less custom made anyway.
A 2 stroke diesel would still have fuel injection except ignition would require another means beside high pressure, i. e., a spark and/ or the bunker would need to be heated to a higher temperature before injection.
A compressor unit could supply the air.
The displacement would need to be several times larger for the same power and the recuperator would add to the size, but that isn't an issue on a ship.
Bret Cahill