Best Prop Pitch For A Pontoon Boat
Prop pitch or propeller pitch is important and determines the speed and acceleration of a boat. The pitch indicates the total number of inches the propeller will move through the water in one blade revolution.
Because pontoon boats aren't built for speed, we don’t need to only focus on the fastest prop pitch. However, it’s possible to go too slow with a propeller that simply doesn’t provide enough power.
The most common prop pitch options for a pontoon boat include 13 inches, 16 inches, 19 inches, 21 inches, and 24 inches.
We found the average pontoon boat has a speed of around 25 MPH and a cruising RPM of 4,500. The most common gear ratio is also 1.85:1.
We will use these factors below to explain how the different prop pitch impacts the propeller slip and boat efficiency, along with what the best prop pitch for a pontoon boat is.
13-Inch Prop Pitch
The 13-inch prop pitch is the best one for a pontoon boat because these boats won’t drive at excessive speeds. They also don’t need much power to reach their cruising speeds.
When driving a pontoon boat with a 13-inch prop pitch at 25 MPH and 4,500 RPMs, expect a propeller slip of around 15%. This is exactly what we need for our boat to drive with confidence and proper power distribution.
16-Inch Prop Pitch
Assuming the factors mentioned, a 16-inch prop pitch would cause a propeller slip of 32.16% when cruising at 25 MPH and 4,500 RPMs.
A slip above 15% is considered below average when analyzing efficiency, but it’s not exactly the propeller's efficiency. Because pontoon boats don’t typically drive too fast, this is around where it should be.
The propeller slip will also increase at lower speeds; as a boat moves faster, the slip decreases. We would still consider a 16-inch prop pitch for a pontoon boat.
19-Inch Prop Pitch
Next, we can look at a 19-inch prop pitch and how it would perform based on our guidelines and industry average factors. Because this prop will go faster, it can be expected the slip will increase significantly.
Assuming the boat travels at 25 MPH and 4,500 RPMs, the expected propeller slip is about 42.5%. This is high and inefficient for cruise speeds with a pontoon boat.
However, this pitch is best for pontoon boats with slightly higher cruise speeds between 35-40 MPH. This allows the propeller slip to drop between 8-20% for more efficient driving.
21-Inch Prop Pitch
As we increase the prop pitch size while keeping the power, gear ratio, and speed the same, we can expect more propeller slip. This is why we don’t typically recommend a 21-inch prop pitch for pontoon boats unless it can reach much faster speeds above 40 MPH.
According to our estimates, when this prop pitch rides at 25 MPH and 4,500 RPMs while maintaining a 1.85:1 gear ratio, there is a propeller slip of 48.3%.
This is extremely inefficient and simply moves too fast for this boat. This can cause the motor to run below the WOT range, resulting in engine lugging.
24-Inch Prop Pitch
Lastly, we considered the 24-inch prop pitch much too powerful for the average pontoon boat maxing out speeds between 25-30 MPH. This results in a propeller slip of 54.77%.
It’s almost a certainty to run the engine below the WOT range too. We would avoid this prop pitch unless the pontoon boat regularly reaches speeds closer to 60 MPH at maximum RPMs, which is unlikely.
Prop Pitch For A Pontoon Boat Explained
The propeller on a pontoon boat or any boat works like a screw and turns through the water. This movement varies in speed and impacts how quickly a boat can move, its fuel efficiency, and much more.
The way the propeller moves is known as the prop pitch. This is defined as the distance the propeller moves forward in one rotation.
The propeller pitch is defined in total inches per rotation. So when we say a 16-inch prop, we mean the propeller will push the boat forward 16 inches for every rotation.
The easiest way to explain prop pitch is by examining the propeller further. This includes both the diameter and the pitch.
Propeller Diameter
The propeller diameter is the horizontal size of the prop. The easiest way to measure this is to think of the propeller as one big circle, with the outer edge as the point on each propeller blade.
The diameter is the total distance from one end of this circle to the other. The propeller's diameter will vary depending on the desired pitch and RPMs needed for the propeller to function properly.
When the diameter is larger, this means there is more blade surface area. Larger propeller diameters also mean increased RPMs, power, and thrust to power the boat.
Propeller Pitch
Next, we can look at the propeller pitch with a better understanding. The pitch changes based on many factors, but the propeller diameter is one of the big ones to consider.
When the number of inches per rotation increases, the speed also increases for a particular propeller. However, simply upgrading the pitch to go faster isn’t possible for all boats because it also requires increased power to run safely.
The desired RPM operating range can be achieved with enough power for the prop pitch. This is something that needs to be confirmed before trying to push a pontoon boat with an increased pitch.
How To Choose The Best Prop Pitch For A Pontoon Boat
When deciding on the best prop pitch for a pontoon boat, no single answer applies to every boat type and person. Many factors are worth considering, and we are here to make it easier to understand.
Some of these factors include the desired or recommended RPMs, propeller material, boat size, engine size, rake, slip, and blade thickness.
Check The Recommended RPM
The recommended RPM on a pontoon boat is typically between 4,500 RPM and 6,000 RPM when driving it. The maximum RPM is usually around 6,000 RPM, while the average is around 4,500 RPM.
Checking the exact recommended RPM in the owner’s manual of a boat is critical when considering prop pitch. The cruise speed RPM will impact what prop pitch provides the least amount of propeller slip.
Propeller Material
It is important to consider the material of the propeller on the pontoon boat. This will impact the proper prop pitch and how much it will impact the boat’s speed.
The most common propeller material is aluminum, but stainless steel has become more popular because they are stronger and more efficient in water.
This material type is important for prop pitch because a steel and aluminum propeller will work much differently.
Boat Size
Next, consider the size of the pontoon boat when choosing the best pontoon boat prop pitch. Typically, the larger boats require more power to operate, which means higher RPMs too.
When this happens, the prop pitch must change, or else there will be too much slip when reaching both cruising and max speeds in the water. The same is true for the number of propeller blades used.
Engine Size
Engine size is such an important factor because of how much the propeller diameter and size can change based on the engine. Typically, smaller-diameter props use smaller engines to balance power and speed.
When this happens, our prop pitch must change too. We recommend learning about the pontoon boat’s engine before getting involved with the propeller and prop pitch settings.
Slip
We have mentioned propeller slip quite often. This is an extremely important factor for all boats when discussing prop pitch.
The slip identifies the difference between the actual propeller performance based on various factors compared to the theoretical performance.
So if a 16-inch prop should move 16 inches per rotation, the slip percentage identifies how much that is off. The slip percentage should ideally be between 8% and 25%.
Blade Thickness
The thickness of the propeller blades will impact how fast they move and how much they drag in the water. Thinner blades will have reduced drag, so there is less slip, and the pitch is more accurate.
Rake
Rake is another factor worth considering. This is the angle the propeller blade factors on the boat and determines pressure levels and water preservation.
It directly impacts speed, so when a blade faces backward toward the rear of the propeller, the blade rake increases. Pontoon boats use low rake blades because they bite the water better for more efficiency.
Gear Ratio
The gear ratio is the number of drive shaft revolutions for each propeller revolution. When this number is 1.85:1, it means for each propeller rotation, there are 1.85 engine drive shaft rotations.
This directly changes how much slip can be expected and the amount of power needed to reach certain speeds.
Why The Right Prop Pitch Is Important For A Pontoon Boat
Without experience in the water and driving or working on boats, a term like prop pitch gets overlooked by the novice pontoon boat owner. However, it’s much more important than it seems.
The right prop pitch is necessary for a pontoon boat because it will help provide the proper driving power, acceleration, and engine efficiency.
Proper Driving Power And Acceleration
The boat gains more power and improved acceleration when the prop pitch gets lowered. But this can vary based on the boat type.
Top-end speed is not a priority with a pontoon boat, so it doesn’t make sense to aim for a higher prop pitch. This is why most pontoon boats see success with a 13-inch prop pitch or even a 16-inch prop pitch.
Engine Efficiency
Secondly, the prop pitch will impact engine efficiency. Running a high prop pitch on a boat that doesn't need it can cause the engine to run below the WOT range.
When this happens, the engine lugs and adds more stress to the engine and engine components. We don’t recommend doing this because it can cause expensive damage.
Should You Use A 4-Blade Or 3-Blade Prop For A Pontoon Boat?
The propeller is one of the most important parts of a boat, and it must be in good condition. The number of blades on a propeller can vary, but there are some things to be aware of when purchasing one.
Typically, the decision is whether to use a 4-blade or 3-blade prop. The various factors mentioned above will impact this decision, but 4-blade props run better.
In general, 4-blade props are better for boats carrying heavy loads or not getting enough power from their engines because they provide more thrust than 3-blade props.
4-blade props also work more efficiently but run one inch lower in pitch because of the extra blade. This will also impact what prop pitch works best for a specific pontoon boat.
