Adding a fan to a sailboat might help you stop said sailboat. Adding a fan to a swamp boat is not stupid and does work.

www.airliners.net/forum/viewtopic.php?t=738011

I tried to find a figure for what percentage of the normal operating thrust a thrust reverser configuration can provide and couldn’t readily find that info. However, according to that forum, thrust reversers only really reduce stopping distance by 10% or so and are deployed primarily to help maintain control in case there is uneven braking due to poor runway conditions.

Also, multiple sources say thrust reversers only work effectively at high speeds, and lose effectiveness at low speeds. I didn’t find an analysis on why that is the case, but it has something to do with the flow rate of air through a jey turbine being much lower at low speeds.

A sailboat will always be at low speeds relative to the wind. A thrust reverser configuration might provide some usable thrust, but you would be much better off just using the fan directly for propulsion and skip the sail altogether. Even that is very inefficient compared to propelling against water.