Just as feet need shoes of the right size, boats need outboard motors of the correct shaft length. If you find your Yamaha Enduro Boat Engine isn't moving fast in the waves, or the propeller suddenly spins when turning, don't doubt the horsepower; instead, consider whether the boat motor's shaft length is appropriate.
When choosing an outboard motor, don't just focus on horsepower, brand, or price; you also need to pay attention to the shaft length. Imagine running a marathon in ill-fitting shoes-even if the shoes are expensive, the run will be uncomfortable and painful. Today, let's understand how to correctly measure the shaft length of a marine motor.
What Exactly Is The Shaft Length Of An Outboard Motor?
The lower part of the outboard engine is that long leg, extending from the mounting plate that connects to the hull to the propeller. The length of this leg is the shaft length. Officially defined, the shaft length is the vertical distance from the top surface of the mounting plate to the anti-vortex plate above the propeller.
The anti-vortex plate is that horizontal metal plate above the propeller that looks like a small wing. The primary function is to prevent the propeller from drawing in air from the water surface during operation. Shaft length ensures that the propeller and anti-vortex deflector are positioned optimally in the water.
How Do You Manually Measure Your Correct Shaft Length?
First, measure your freeboard:
Locate the stern plate, the vertical plane at the stern where the engine is mounted. Find your measuring tools; a long measuring tape will suffice. Position the boat on level ground and locate the area on the stern plate where the outboard motor will be installed. Measure vertically downwards from the top of this area to the lowest point of the hull. Ensure the measuring tape forms a perfect 90° angle with the stern plate.
Remark: If the stern plate is stepped or recessed, you must start measuring from the top of the recess, not from the deck surface.
Then, based on your freeboard and the corresponding standard shaft length, select the appropriate outboard motor marine engine.
• If the freeboard is 38-43 cm, a short-shaft outboard motor should be selected.
• If the freeboard is 50-56 cm, a long-shaft outboard motor should be selected.
• If the freeboard exceeds 63 cm, an extra-long-shaft outboard motor should be selected.
Remember: After installation, in still water, the anti-vortex plate should be 2.5 cm below the waterline. Of course, the measured value is only a baseline; adjustments need to be made based on your specific usage scenario.
• If frequently fully loaded, the hull draft will be deeper, so consider selecting a shaft length one unit longer than the measured baseline.
• If frequently in open water or at sea, to prevent the propeller from idling above the waterline in waves, a slightly longer shaft is needed.
How to verify correct installation?
A simple sea trial will tell us the final answer. While sailing in a straight line in calm water at a moderate speed:
• Observe the anti-vortex plate: If the anti-vortex plate is completely submerged, you can see the water flowing smoothly over it.
• Test a sharp turn: Under safe conditions, make a moderate sharp turn and observe whether the propeller breaks the surface of the water due to the boat's roll. If it doesn't, it's good.
• Experience overall performance: The correct shaft length results in smooth acceleration, higher efficiency, and less vibration.
Properly measuring and selecting an outboard motor with the appropriate shaft length, though often imperceptible, ensures everything is just right, such as smooth acceleration, stable turning, and low fuel consumption. Take ten minutes, grab a measuring tape, and find the right outboard motor engine for your boat. After all, on the water, every step should leave no trace. For more information about the Yamaha Enduro Boat Engine, please contact KLS Factory:
• +8615094051894
• inquiry@klsautoparts.com
• Room 1705, Yihe Blue Diamond, No. 154, West Section of Second Ring South Road, Yanta District, Xi'an City