Fishermen and others use trolling motors when they want to move quietly around a body of water. While trolling motors can be attached to and used on a wide variety of boats, the size of the boat and the length of the trolling motor shaft, which is the area of the motor between the head and the prop, must be in line. Measuring the length of the trolling motor shaft is necessary before anglers can properly determine which trolling motor fits on their boat. Place the trolling motor on the ground so the shaft faces upward. This should be done on a dry,steel shaft, hard surface. The shaft is the part of the trolling motor between the head and the prop. Using a tape measure, measure that distance. Record the distance, noting that the length of most trolling motor shafts are in increments of 1 foot (such as 36 inches, 48 inches or 60 inches).