Measure the transom height of your boat as indicated above. If your measurement is in the range of 15" to 17" you will require a short shaft outboard. Approximately 19" to 21" is a long shaft and if your in the area of 24" to 26" then you will need an extra long shaft. Newer larger boats are also built with a transom height of 30". This would be considered an extra-extra long shaft.
Whether purchasing a new or used outboard, knowing the exact measurement in inches is necessary to determine the required shaft length outboard you will need to buy. You cannot use an outboard that is shorter or longer than what your boat requires.