How to size trolling motors?

[ShoestringMariner]

Hey guys, I’m wondering how to size trolling motors.

I have a 16 foot aluminum boat. I’m considering putting a gas trolling motor on the back and possibly a bow mount as well. Because the mercury outboard that came with it is pretty old, I’d like something I can get me back to shore or launch safely.

generally speaking though, how do I calculate what size trolling motor I need. For a gas trolling motor on the back I’m assuming 5 to 8hp? (I generally fish on smaller lakes) 40 pound thrust on a bow mount?

if there’s a general rule of thumb that would be great

 

[roscoe]

Have a 4 hp that we have used for years on several different boats, including a 1996 Alumacraft LTD.
It has pushed us back up the river in Canadian wilderness several times, slow but steady.

Also used it on a 17' boat for trolling, but was not real happy with the control in windy conditions.
One really nice thing is the built in gas tank, holds 3/4 gallon, can troll for over 11 hours, and no extra gas can in the way. And easy to tilt up when you want to use the main motor.