How to Measure an Outboard Shaft Length

Measure an Outboard Shaft Length Step 2

How to Measure an Outboard Shaft Length

Measuring the outboard motor shaft length is just as important as choosing the motor itself, but luckily the process is relatively quick and easy. On the other hand, the boat’s efficiency and safety depend on your choice.

In this article, you will find a detailed illustration and step-by-step instructions for measuring the outboard shaft length.


Measure Shaft Length

To perform the necessary calculations, you need to prepare a tape measure or another tool convenient for you to take measurements. Prepare a pen and a piece of paper, or you can write everything down on your phone. You need to measure three lengths; the whole process includes three simple steps.


  1. Locate the transom top and the lowest point of the boat hull and measure the distance between them as shown below.Measure an Outboard Shaft Length Step 1
  2. Then, it would be best if you found the radius of the propeller. You can find the radius of the propeller in the owner’s manual, or you can find a diagram on the internet using the name, model, and year. You can take measurements yourself, but it is always helpful to double-check the data. When you find the propeller radius, see the examples below, add the transom height you calculated earlier to it, and the get number is the minimum shaft length.Measure an Outboard Shaft Length Step 2
  3. Whenever you are ready, add 10 cm to the resulting value and get the ideal shaft length for your boat.



So, let’s keep in mind the calculations that are written above and given below for the ideal shaft length recipe:

  • Transom height + Propeller Radius + 4 in (10,16cm) = ideal shaft height

For example, let’s take a boat with a transom high of 20 in (50,8 cm), and the engine’s propeller will be 5 in (12,7 cm). Then, to find the shaft that suits the boat, we need to complete the following calculations:

20 in + 5 in = 25 (minimum shaft length to make it work)

20 in + 5 in + 4 in = 29 in (perfect shaft length)

When the most straightforward part is done, you can continue with your purchase decision and install everything together for future recreations.

In case you have any additional questions feel free to ask! We hope that the article helped and would like to invite you to go through our selection of motors and shafts with all the needed dimensions and characteristics. Our expert will guide you through an extensive choice of outboard motors and shafts from ePropulsion, ThrustMe, RIM, and TEMO.


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