Start with a large barge, fill it with trash, ignite the composting
trash which creates an updraft which you capture with a 'fan', which
turns a screw propeller.
Or take the same trash, bury it deep in the sea floor, wait a few
million years until the carbon content either becomes oil or coal, re-
invent an internal combustion engine (AlGore® etc. in the meantime
will have decrepitated all forms of modern energy sources to whale oil
blubber wick oil lamps) ... and then drive the boat with reinvented
engine.
OR take the same barge and fill it with several million pounds of
carbon neutral baking soda, in a separate container add a few hundred
thousands pounds of acid; mix the two in a proportioning nozzle ....
to create a 'jet' out the back end of this 'water world' miracle.

I have/propose a better solution:
1. Mandatory back-breeding of the human species until humans are again
18 inches tall and consume less of the so-called 'environment'.
2. Sperm Control: when you're born, ...... if your lotto number is
wrong your willy gets whacked off
..... both very simple.
g ;-)