Nice work, assuming the welds are sound. it would be interesting to see how long it takes to get the motor out and mounted, started and getting underway when a big barge or other commercial vessel is about to run you down. In your pictures it looked like your boat was about 30 feet. 3 to 4 HP may push it in calm waters with minimal current. If you have any chop where you are going you will need the longest shaft you can get or you will be "spinning your wheels". I guess it all depends on how often you will have to use it as to whether you leave it on permanently or mount it each time you need it. 3 to 4 HP seems kind of whimpy but it is a whole lot better than nothing. Curious about your battery charging capabilities?