Outboard Motor Shaft Length

                                          Outboard Motor Shaft Length:       How do I measure?


                                  If mounting directly to a boat transom: Measure from the top of the transom down to the bottom of the hull
                                 or keel (lowest point).   Measure the area of the transom directly where the engine will be mounted. 
                                 This measurement is primarily designed for single motor propulsion.   A deep Vee hull will result in a different
                                 measurement than a flatter bottom hull.   As you will see in the chart below there  is nothing set in stone.
                                 Each motor (depending on the hull design) may have to be fitted (raised or lowered) for optimum performance.
                                 Tip:   If you are using a auxiliary motor on a shallow Vee hull where the main power is a jet in a river where you
                                 may be fishing in shallower & changing water, then the shortest shaft (even with the anti-cavitation plate slightly
                                 above the hull bottom) may save the prop from a bad case of rock rash.          See diagram below.

                                  If using an auxiliary mounting bracket: With the bracket in the down position, measure from the top of the
                                 bracket’s mounting surface down to the bottom of the hull or keel (lowest point where engine will be mounted).
                                 Tip:    For most auxiliary applications, it is possible to use a longer shaft length than what is called for, provided
                                 there is sufficient clearance when the engine is in the up position.   This can be especially useful in heavy seas.

                                 If measuring an existing outboard: Measure from the inside top of mounting bracket down to anti-cavitation
                                plate above propeller (this is the largest plate/fin directly above the propeller). See diagram below.

As you will see the 15" standard shaft length is only an average

Height Measurement: Recommended Shaft Length: 14” – 17.25” 15” Shaft (Short) 17.25” – 19.5” Varies by application 19.5” – 22.5” 20” Shaft (Long) 22.5” – 27” 25” Shaft (Extra-Long)