[bmdavi3]

I don't know if the strength of an LED is enough to move the craft significantly, but if it is you'd need to point it at anything _but_ the ship itself, otherwise the two forces would cancel out. Just shine it in the opposite direction of where you want to go.

[umvi]

No, the two forces don't cancel out, I can't remember exactly why but elastic collisions don't work like that. That's why you can point a fan into your sailboat's sail and it will still go forward, mythbusters proved it.

[mkl]

Mythbusters demonstrated something different, and something much less efficient than simply pointing the fan backwards like a normal fan boat (no sail required). Here: https://mythresults.com/blow-your-own-sail