Proper Propping: Getting the most from your boat’s performance
Selecting the correct propeller is a critical factor in maximizing your boat’s performance.Choosing the correct size and style of prop for your boat will keep the engine operating within its recommended rpm range and allow it to harness as much of its horsepower as possible.
Size DOES Matter:
Prop measurements have two key designators: diameter and pitch. Diameter is determined by doubling the distance from the center of the hub to the tip the prop’s blades. A good rule of thumb is smaller diameter props are typically used with smaller engines/boats, and larger diameter props are typically used with larger engines/ boats.
Pitch measures the forward movement of the propeller’s blade during one complete revolution. This is measured in inches. Lowering prop pitch will increase acceleration and thrust. Increasing prop pitch will make the boat go faster (provided the engine has enough power to keep the RPMs in the optimum operating range. If the engine doesn’t have enough power to run a higher pitch prop, performance suffers across the board and you could easily damage your engine. A good test is, if the prop lets your engine operate at Wide Open Throttle (WOT) within its correct rpm range, you’ve got a good prop fit.
Number of Blades. How it adds up.
For years, boaters have debated the question of 4-blade propellers versus 3-blade versions. (The traditional argument is that 4-blade props are slow and 3-blade props are
fast.) Today, with higher fuel prices and tighter economic times, boaters are taking a second look at this debate. Speed is now a much smaller part of the boating equation. In turn, practical, real-world performance is the name of the game for most people. So, which props should you be using, 4-blade or 3-blade? Traditionally, the idea that 4-blades were slower than 3-blades was true to some extent. But what you need to keep in mind is that many of those 4-blade props were not designed with speed in mind. Instead, the earliest designs were intended to cure handling issues such as ventilation, cornering blowout, motor elevation requirements, and hole shot issues. Without many options in blade design, and very few of them truly intended to be particularly fast, the 4-blade got branded as slow, while their other performance benefits were largely dismissed.
In contrast, today’s 4-blade propellers have evolved into both all-purpose and highly specialized designs. This new generation of props can be tailored to not only address those traditional handling issues, but can also be tailored to improve a boat’s performance range, which can, in some cases, include speed.
Before making a choice, determining your performance priorities will help you determine your prop choice.
Cupped Boat Propellers
Special curved trailing edges enable the prop to maintain performance at higher trim levels and in tight corners. Cupped boat props allow most boats to achieve a higher top-end speed or at least the same speed at a lower engine RPM. They also promote more efficient fuel consumption.
Material is not immaterial.
Propellers can be made of composite, aluminum, and stainless steel. Composite boat props offer good performance, are durable, and inexpensive. They also offer some protection for your lower unit during a prop strike becoming something of a sacrificial lamb. Aluminum props are the most common and are suitable for the widest range of applications since there are so many models and styles available. Stainless steel props offer the highest performance—due to their lack of flex—and best durability.
The chart below is a handy comparison:
Spare yourself the pain…carry a spare.
Finally, always have an extra propeller on board with tools allowing you to change it out. If you have a prop strike or spin out a hub, you will only be delayed a few minutes and not miss out on any for or worse—be stranded.