First of all, welcome to our little Yamaha Enduro Outboard Motor science channel! When you're still struggling to decide which shaft length outboard motor to buy for your beloved boat, or if you're a novice in the industry and can't decide between long-shaft and short-shaft outboard motors, don't be afraid, don't worry, and don't be anxious, because you're not alone.
Most boat owners encounter this seemingly simple but actually crucial question when buying their first outboard motor: long-shaft or short-shaft outboard engine? Actually, this question isn't complicated. As long as the boat owner understands their boat's sternplate height, sailing environment, and the definition of shaft length, they can easily determine the most suitable choice for their vessel. Let's explore the answer to this simple question together!
Definition Of Outboard Motor Shaft Length
The shaft of an outboard motor boat engine is the middle part connecting the engine head and the propeller. The shaft length is the length of this middle part. The design purpose of the outboard motor shaft is to ensure that the propeller is at the optimal depth below the waterline. Based on the length of the long shaft, there are three types: short shaft, long shaft, and extra-long shaft.
• Short shaft: approximately 38cm;
• Long shaft: approximately 50cm;
• Extra-long shaft: approximately 63cm;
Why Choose The Right Shaft Length For Your Boat?
Think about it: a suitable shaft ensures the normal operation of the boat. If the shaft length is unsuitable, it's like wearing ill-fitting shoes; the boat simply cannot move forward properly.
If the shaft is too long, the propeller is embedded too deeply, increasing drag, fuel consumption, and speed. Although it can still move clumsily, the bow is raised too high, making handling extremely difficult.
If the shaft is too short, the propeller is too close to the water surface, or even above it, easily leading to the propeller "loosening" or "malfunctioning propeller." When the propeller is loosening, power is rapidly lost, the engine vibrates violently, and the engine speed increases abnormally.
Correct shaft length matching not only affects performance but also the engine's lifespan. Outboard marine motors rely on water pumps for cooling. If the water inlet is too high, the pump cannot draw water properly, causing the engine to overheat and become unusable, potentially damaging it. Therefore, choosing the appropriate shaft length for your vessel is crucial.
Measuring The Sternplate Height To Determine Whether A Long-shaft Or Short-Shaft Outboard Is Needed
Measuring the sternplate height is simple. First, ensure the vessel is on level ground. Locate the center of the stern and measure the vertical distance from the top edge of the sternplate to the bottom of the hull. Remember: the hull must be level during measurement, and the shaft length must be the vertical distance.
If the measured shaft length is 38cm, choose a short-tail outboard motor; if the measured shaft length is 50cm, choose a long-tail outboard motor.
In other words, for smaller distances, choose a short-shaft outboard motor; for larger distances, choose a long-shaft outboard motor. Matching the height ensures the propeller operates at the ideal depth.
| Item | Long Shaft Outboard Motor | Short Shaft Outboard Motor |
| Shaft Length | 50CM | 38CM |
| Sternplate Height | 19-21Inches | 15-17Inches |
| Weight | 41KG | 38KG |
| Displacement | 246CC | 246CC |
Which Vessels Are Suitable For Short-Leg Outboard Motors?
Lightweight, shallow-draft boats with low stern plates are well-suited to short-leg outboard motors, such as small fishing boats, inflatable boats, and small recreational kayaks. Of course, if the boat owner prefers portability and lightweight power, or frequently navigates shallow rivers and lakes, a short-shaft outboard motor is a more suitable choice.
Which Boats Are Suitable For Leg Outboard Motors?
Boats with higher stern plates, greater weight, and more stable hulls are better suited to long-leg outboard motors, such as aluminum alloy boats, fiberglass boats, and medium to large fishing boats. Long-wheelbase outboard motors are better suited for navigating wavy waters. If you frequently operate in bays, along coastlines, or in rougher waters, a long-shaft outboard motor is a more suitable choice.
Properly Matching Shaft Length Is Crucial For An Outboard To Perform At Its Best
Many novice boat owners neglect shaft matching when buying their first outboard motor, resulting in a purchase that is not a good fit for their boat. If the shaft length and stern height are mismatched, even with sufficient engine power, propulsion efficiency will decrease, the propeller will spin, the engine will overheat, or water will splash everywhere.
Conversely, if the shaft length and stern height are correctly matched, the boat owner will experience smoother acceleration, more stable propulsion, higher fuel efficiency, a more stable voyage, and a more pleasant experience.
Still unsure how to choose? Here's a tip:
If you're a used boat owner, check the original outboard motor model. "S" represents a short shaft, and "L" represents a long shaft. If you're not a used boat owner, observe the propeller position. With proper shaft length matching and installation, the anti-aircraft plate above the propeller should be flush with the hull or slightly lower. The most direct method is to contact the outboard motor supplier KLS Company directly; they will provide the most professional matching solution.
If you're a new boat owner planning to purchase an outboard motor, before focusing on brand and price, be sure to confirm the shaft length and horsepower to avoid unnecessary trouble. Choosing the right outboard motor is essential to fully enjoy the pleasure of sailing on the sparkling water. Have you already measured the sternplate height of your vessel? If you are unsure of the exact measurement point, contact KLS Company, and we will recommend the most suitable outboard motor based on your vessel type:
• +8615094051894
• Room 1705, Yihe Blue Diamond, No. 154, West Section of Second Ring South Road, Yanta District, Xi'an City
References:
Wikipedia Outboard Motor.
How To Measure Shaft Length Outboard Motor?