Selecting Correct Shaft Length

Choosing the Right Shaft Length for Your Outboard Motor

When selecting the appropriate shaft length for your outboard motor, it’s important to understand how this measurement affects your boat’s performance. The shaft length determines the distance between the boat’s transom and the propeller, which influences the propeller’s immersion in the water and its ability to generate thrust. (practical advice) Most boats will be long shaft version unless is a very small RIB. 

How to Measure for Shaft Length

To accurately determine the shaft length needed for your boat, you will need to measure the distance from the top of the transom mount point (where the motor attaches to the boat) down to the center of the propeller when the motor is installed.

Here’s how to take this measurement:

1. Find the Transom Mount Point: This is the flat surface at the stern of your boat where the outboard motor is mounted.
2. Measure Vertically: Use a tape measure to measure from the top of the transom mount point (where the motor is attached) down to the center of where the propeller will be when the motor is mounted.

Shaft Length Variations for Our Outboard Motors

For our outboard motors, we offer two shaft lengths:

• Short Shaft: 675mm (24.6 inches)
• Long Shaft: 750mm (29.5 inches)

These measurements reflect the distance from the top of the transom mount point to the center of the propeller. Choosing the correct shaft length ensures that your propeller remains properly submerged for optimal performance, providing efficient propulsion and maneuverability.

When to Choose a Short Shaft (675mm)

A short shaft is typically used for smaller boats or those with a transom that is closer to the water’s surface. This shaft length is ideal for:

• Small boats with lower transom heights.
• Shallow water applications where you want the propeller to sit closer to the surface.
• Boats where the transom is 15–18 inches above the waterline.

When to Choose a Long Shaft (750mm)

A long shaft is generally used for larger boats or boats that have higher transoms. This shaft length ensures that the propeller is deep enough to provide consistent thrust, even in choppy or rough water conditions. A long shaft is recommended for:

• Larger or heavier boats with higher transoms.
• Deep-V hull boats that require the propeller to be positioned further into the water.
• Boats where the transom is 20–25 inches above the waterline.

Why Shaft Length Matters

Choosing the right shaft length is crucial for maintaining proper propeller depth. If the shaft is too short, the propeller will be too close to the water’s surface, reducing its efficiency and potentially causing cavitation (air bubbles forming around the propeller). On the other hand, if the shaft is too long, the propeller could be too deep, increasing drag and reducing fuel efficiency.

How to Adjust for Your Boat’s Specific Needs

Each boat is unique, and factors such as hull design, load, and water conditions can impact the ideal shaft length. If you’re unsure which shaft length is best for your boat, consider the following tips:

• Consult your boat’s manufacturer specifications: Many boat manufacturers provide guidelines on the recommended outboard motor shaft length based on the transom height.
• Test for optimal performance: If possible, try different shaft lengths to see which provides the best performance for your specific boat and water conditions.

By understanding the relationship between the transom height and shaft length, you can make an informed decision that ensures the best performance and durability of your outboard motor.

Summary

• Short Shaft: 675mm (24.6 inches) – Ideal for boats with a transom height of 15–18 inches.
• Long Shaft: 750mm (29.5 inches) – Ideal for boats with a transom height of 20–25 inches.

Always remember to measure your boat's transom carefully and consult with your outboard motor supplier or manufacturer to select the most suitable shaft length for your needs.

As of May 2025, the short shaft length of this model has been updated from 625 mm to 675 mm. This small (approximately 2 inch) adjustment is within industry-standard tolerance for short shaft outboards and does not affect compatibility with standard 15″ transoms. The change is functionally insignificant and does not impact installation, performance, or warranty. Updated measurements reflect improved alignment with typical transom mounting depths and common industry practices.