Re: Drive shower????
In most cases, they will increase the life of your drive about as much as a differential cooler will increase the life of the rear end of your car or truck. When is the last time you worried about that? Unless you're a NASCAR racer, it's probably never occurred to you.
What kind of boat is it, and what kind of drive is it?
Unless you are running well over 500 HP, it's there just to look cool as far as the life of the drive is concerned.
If the water you boat in has a lot of dissolved calcium and you're having problems with white calcium deposits on your drive upper, they'll supposedly help with that.
For a typical pleasure boat capable of less than 70 MPH, they won't hurt, they're pretty cheap, and will possibly impress people who don't know any better!