Deciding on whether to buy a 12v or a 24v trolling motor depends on how much power or thrust your boat needs.
And a general rule when choosing a trolling motor for your boat is to have 2lbs of thrust for every 100lbs.
Typically, trolling motors are measured or rated using what is referred to as pounds of thrust.
So if you have a boat that weighs 3500 pounds that is fully loaded, to know how much thrust you need, you simply divide 3500 by 100 and then multiply the result by 2.