Ask anyone that's been in my boat, that trolling motor is very powerful and the 36V system doesn't run down; even after a long day at the office

. Sure it will push your 20 footer, but can you effective operate it and fish from the stern, those are the questions. Interesting you ask about putting a bow mount trolling motor on the stern of your 20 footer, but it's likely the only way you will get that thrust. Almost all the most powerful motors are limited to bow mount application, but then again it's been awhile since I looked at what is available.
If the shaft length works yes it will work, but I'd definately recommend a 36V system for any prolonged salt water use. There are motors that can be mounted on your lower unit and the usual transom mount motors, however I'm not sure they have the balls you would need. Might go to either the motor guide or minn kota web pages to see what is available, maybe even give their customer service people a call.
The quiet power that catches fish

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