I want to increase the speed of my 12v DC trolling motor
I agree.  Your time has value.  But solutions also have value.  I hope you think better of your time than wasting it on dead-end fantasy solutions that aren't going to happen.
The problem with maritime power is that energy requirement is quadratic to speed - that's why boats cruise slower than max speed. So you're talking about a considerable amount of energy and that'll mean bigger motor, bigger battery and bigger controller.  Trolling motors are for trolling.
A lot of people are working on Electric Vehicles for over 30 years, and there's an astounding amount of tech out there designed for vehicle builds and conversions.
Your best bet will be finding an outboard motor that will give you the speed you want, and strip out the gas engine. (needless to say, units with known-bad gas engines are a good choice). Replace it with a right-sized electric motor and controller from the vast catalogs of the electric vehicle suppliers.  I'm sure you won't be the first on the lake to do that.
The best combos these days are dog-simple 3-phase AC induction motors and fairly sophisticated motor controllers.  An AC motor has no moving parts.  By which I mean the spinning rotor is entirely passive, just a hunk of aluminum.  This means if you swamp the motor, it's easy to tear down and clean up - the electrical parts are simple coils, and are potted.  If they're messed up, any competent motor shop knows what to do with it.
The smarts/guts are in the controller.  That, you need to carefully seal in a watertight box.  It may have a water line in/out for cooling, but your outboard motor probably already has a water cooling loop for the old engine.
Then it's just a matter of a big enough battery to provide the range you want.