The shaft length is one of the most important factors to consider when purchasing an outboard motor.
- An outboard motor that has the incorrect shaft length can cause performance and handling issues. That is why it is extremely critical to measure the outboard shaft length accurately.
This guide will walk you through the process of measuring outboard shaft length correctly so that you ensure you have the right size motor for your boat
Consequences of incorrect shaft
- Short shaft on a high transom: Propeller may not fully submerge causing cavitation as well as loss of power
- Long shaft on a low transom: The Propeller may hit the bottom of the hull which can impact performance and maneuverability.
- having too long of a shaft can result in a propeller that sits too deep in the water which causes drag as well as reduced speed.
- Having to short a shaft can result in having the propeller sit out of the water and can result in loss of power and eventually lead to overheating of the engine.
Step 1: Gather the Required Tools
- You'll need a few tools before you start measuring.
- Tape Measure (Make sure your tape measure is at least 25 feet long so you can accurately measure the shaft length)
- Level
- Straightedge
Make sure your motor is positioned vertically and make sure to use your level to make sure the motor is correctly aligned. (if you are planning to operate your boat in rougher waters you can add a few inches to your final measurement.)
Step 2: Calculate the Proper Shaft Length
- The top of the outboard motor should be level with the bottom of the boat as a general rule. This ensures that the motor is at the proper height for maximum performance and will not result in any issues.
- A short shaft outboard motor is required if the distance between the top of the transom and the bottom of your keel is less than 15 inches.
- A long shaft outboard motor is required if the distance is between 16 and 20 inches.
- For distances between 21 and 25 inches, you will need an outboard motor with an extra-long shaft.
Step 3: Examine the Manufacturer's Suggestions
- Check the manufacturer's recommendations for the appropriate outboard shaft length for your specific boat model. Depending on the manufacturer's recommendations sizes may differ from the general rule of thumb, it's crucial to follow their instructions for the best results.
Step 4: Final Inspections
- Before buying an outboard motor, double-check the measurements and make sure you have the correct shaft length. It's also a good idea to have a professional double-check your measurements to make sure they're correct.