Did the same when I started pulling cranks, basically the same situation except I had a transom mount trolling motor and mounted it on the back of the boat. Gave me time to get my pennies together and move up to 36v, fished a whole cranking season that way with no issues to speak of. Learn to manage my batteries and those lessons have served me well on bad windy days.
Way to figure it out!!! Good job.
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