A wholly moronic idea
Ah yes, let's see, let's leave it to a non-nautical type to devise a device for use on boats, shall we?
First of all, fouling a propeller of a powered boat in motion isn't only stupid, it's brilliantly dangerous. Why? Well gosh-golly Mr. Genius Boffin, when you foul the propeller and it can't turn, that has the effect of tearing the living Shiite and Sunni holiness out of the little thingy attached to it - I believe it's called an "engine". So, blow the engine, and if it's near fuel - which engines typically are located close to fuel, and there's a risk of this little thing called "fire". And as any nautical type knows, fire on boats is not a Good Thing (TM).
So, "Boffins Burn Boat To Keel With Super-Bazooka, All On Board Burn In Fiery Death" will be the headline. Way to go, science! Keep up the boffo work.