Air as a submersable prupultion

Has any one ever heard of air as a prupultion like a jet drive nozzle but a compresser to a nozzle submersed. I was thinking this would have great shallow water applications as no wories of rocks passing threw an impeller or getting stuck in the grate. The orfice size that is compressing the air would determan the performance aplications much the same as the water jet nozzles do. Do you think 100 mph with the right combination of power to wieght could be optainable with something like this?:idea:

 

the idea is not bad but nature does not work that way
water is but air isnt incrompressable so you lose power that way
in fact waterjets only became usefull when someone
took the nozzles above water and shoot water to water

 

I think that "Momentum Theory" also agrees with what Yipster just said.

If you could spit out lead or something heavier than water, the greater "mass" and therefore momentum might propell you.