Just thought I would put this into its own posting. I have not yet tackled this project, but it is a common topic for older carburated boat owners. I get asked this question a lot!

I have looked into PP quite a bit as far as building my own from parts. In fact I have my cheat sheet right here! If you have a carburated engine we need the older of the two kinds of PP called "Mechanical". It uses a 'servo motor' to control the speed based on the readings from the paddlewheel. The other kind is called DriveByWire or DBW, which will be printed on the master module and it has no servo motor.

Some parts are easy to find on ebay motors or ski-it-again.com (like dash display guage and master module, other are hard to find like the servo motor).

TO build your own PP you would need:
-Servo motor and parts for mechanical hookup (new from PP $275)
-Paddlewheel (new from PP $129)
-Display (can be single or multiline) ($100 used)
-Master Module (brain or cpu) (cannot say DBW drive by wire, the other kind of PP which is much more common) ($100 used)
-I think there is also a wiring harness of some type that PP would likely need to supply you.

Note that a lot of the PP for sale on ebay motors are incomplete.

So the price for all this listed above is $704 or higher depending if you get used or new parts but it could still be missing some wiring or other needed parts. PP brand new is about $1000. I am still not sure if all that hassle of buying used would be worth the savings. PP will support you GREAT even if you try and build your own.

Good luck and post up those good ski-it-again.com finds.