Airplanes deploy revers thrusters when landing which are basically just shaped metal shields that move into place behind the engines to provide reverse thrust and slow the plane.
But adding a fan on a sailboat is seen as stupid and doesn’t work.
The fan is pushing the boat backwards. The sail is pushing the boat forwards, but with slightly less efficiency since the air is losing speed between the fan and the sail. So you’d go slightly backwards.
So.. it would work, just so poorly there’s no reason to bother.
0ops@piefed.zip 4 minutes ago
People have already covered that the jet doesn’t just block air but redirects it (not unlike a sailboat moving across the wind), and really that’s most of it. One differing factor that I don’t see mentioned in here that I think is worth mentioning is that unlike the fan, the jet engine doesn’t merely move air, it heats it enough for pressure to increase before it leaves the engine. So in terms of energy, that added heat has nowhere to go but wherever it’s directed.
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Also sorry about some of the commenters being dicks about answering your question, it’s a good question and people need to remember what this community is for.