Boat Propeller Physics—Insight from Turning Point Propellers

PartsVu Xchange Talks Boating chatted with Phil Stephanuik, Product Engineering Manager at Turning Point Propellers, and Charlie Haimes, a partner with the Haimes Coleman Group, about the physics and characteristics of boat propellers. Based in Jacksonville, FL, Turning Point Propellers is a leader in 3- and 4-blade aluminum and stainless-steel boat propellers for the marine industry. The Haimes Coleman Group is a sales organization made up of highly experienced and knowledgeable marine industry professionals representing twenty of the industry’s leading brands, including Turning Point Propellers. Phil and Charlie share the fundamental physics, advanced characteristics, and tips for selecting and maintaining the best propeller for a given application.

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How do boat propellers contribute to a boat’s performance on the water?

Phil: Besides the tachometer, the propeller(s) is the most important thing on the boat because it is the only thing that moves the boat. Without the correct pitch and diameter, a boat will not perform. Propellers limit the RPM range that motors need to run in. They help control speed, fuel economy, lift, cornering, and hole shot. With such a wide variety of boat, motor, and weight combinations, there are hundreds of boat props to choose from.

Charlie: Unique hull designs affect the way water flows across the bottom of a boat so having the technical knowledge of propeller design helps ensure that the best selection is made for a given boat. There is a vast difference in propellers’ performance; many consumers do not always understand the performance advantages of selecting a high-quality propeller like Turning Point.

What are the fundamental physics of propellers, and how do boat propeller characteristics work together?

Phil: The starting point is the number of blades, which vary from two to six. Blades can be a high or low rake, the rake being the angle they tip out and away from the boat. The higher the rake, the more the angle, which means the hull wants to lift, and the bow comes up.

With an inboard motor, propellers can include flat blades with a constant pitch and sometimes a negative rake. Each propeller has an inner hub barrel through which the engine exhaust flows and an outer hub barrel.

The propeller pitch is from the blade’s leading edge to the trailing edge, which is not always a constant. For example, a 19-pitch prop may start at a 16-pitch and end at a 22-pitch. In simplistic terms, propeller pitch Is the displacement a propeller achieves in a complete 360°-degree rotation.

People don’t really need to understand the geometry of the blades but do need to understand their motor’s RPM. For years, companies came out with props, and others tried to manufacture similar versions. Twenty-five years ago, Turning Point Propellers’ founders thought long and hard about what props to design. We wanted something new and better, which we created by leveraging new geometry and designs.

Charlie: Unlike cars with multiple gear transmissions, boats have only engines and propellers. This means there is only one setting – on. The boat prop has to do everything, performing as a universal application for the hole shot, midrange for fuel economy, and have top end. A great prop manufacturer like Turning Point can give consumers the right prop to fulfill those requirements.

How did years working in a prop shop contribute to your success at Turning Point Propellers?

Phil: I spent almost every weekend testing boat props, and many times while out on the national bass fishing circuit, I got to test new props. At home, I experimented in the marina with their boats and tweaked stock propellers by bending them in different ways, changing the cup, rake, pitch, or diameter.

I saw the results firsthand after many field tests and saw how performance was affected by those changes. But, not all changes were beneficial. It was a lot of learning through trial and error, but more than forty years later, I still have a ball doing this.

Charlie: Propellers are not an exact science. Even with two seemingly identical boats and setups, they may still need two different props to achieve the same results. The medium boats run through is water, and the characteristics vary widely from saltwater to freshwater.

Water has different lifting characteristics and aeration depending on the time of year, whether the temperature is warmer or cooler. With so many variables, we must select the universal prop best meets those demands. For those who race, the wrong prop can be the difference between winning a race or being at the back of the pack.

Are there more advanced boat propeller characteristics?

Phil: I designed a new dual geometry four-blade that is unlike any other in the world right now. It has two different blade designs, with two cleaver blades that are larger in diameter than the two-round ear opposing blades.

When the driver hits the throttle, as the bow comes up, the transom comes up with it. This helps get a flatter, faster acceleration. Most boats running our four-blade propeller can see over the bow. Once up and running, they can start trimming and changing from the cleaver blade that lifts the transom to the rounder blades that lift the bow. The boat is lifted higher out of the water horizontally with our four-blade than most other props.

Charlie: It is an excellent propeller that carries the boat well, minimizing the torque and steering. It fits that universal prop role, providing hole shot, midrange, fuel economy, and top-end speed, especially for single-engine applications. It is my number one selling prop.

Do the number and size of propeller blades affect boat performance?

Phil: Absolutely. Larger and more blades will perform better for work boats that need to push heavier loads. For racing, the high horsepower requires more torque, which leads to a change in diameter, pitch, and the number of blades.

Charlie: Grabbing more water is what makes a boat propeller more efficient. More blades tend to reduce slip by submersing more of the blade surface area underwater. For multiple engine applications, Turning Point’s OS series has a larger blade diameter that works more efficiently than many of its competitors’ products.

How can boaters select the best propeller for their boat?

Charlie: We’ve received many complaints about some of the rubber hub props that some boat builders install before boats leave their factory. If the hub ever spins, the boat may not ever get on plane, leaving boaters to idle their way home or, even worse, be stranded.

We want to ensure consumers get an interchangeable hub built to last. Turning Point Propellers’ MasterGuard series hubs carry a lifetime warranty. Other specialty hubs like their MasterTorq series carry a one-year warranty. This is great because it allows a hub to be used with maybe ten different housings over time, such as in cases where a propeller was damaged.

Another factor when selecting the right prop is fuel economy, which with today’s fuel prices, is a huge concern. In other applications, like bass tournament fishing, boaters want a good top-end prop to get them to the best fishing spots before the other anglers get there.

Phil: Not with all boats, but sometimes, we have witnessed as much as 23% savings in fuel economy with our boat props. Also, the question of whether to buy a stainless steel or aluminum prop is common.

Aluminum propellers are less expensive alternatives to stainless steel. We do not diecast our propellers; we squeeze-cast them, resulting in very stiff aluminum blades that do not flex.

Although aluminum blades are typically about one mile per hour slower, they still offer the same lift, cornering, and hole shot. Another important thing to consider is that we not only make props, but also make a lot of different hubs to fit all the motors. So, that props do not have to be thrown away because they would not fit a particular engine.

How can boaters know when they can repair their boat propeller versus needing to replace it?

Phil: Small knicks do not account for much. Run your finger down the blade. When a rough edge is discovered, it can be lightly filed smooth without removing too much material. For more serious issues, a repair can run from $75 to $150.

Given today’s aluminum props prices, it might be cheaper to reuse our hub and buy a brand-new aluminum prop. For stainless steel props, though, it generally is less expensive to have them repaired by a good National Marine Propellers Association (NMPA) qualified prop shop.

What type of propeller maintenance should boaters do?

Phil: Routinely inspect boat propellers for larger knicks and make sure the blades are not bent. Also, remove the propeller every six weeks. Fishing line tends to wrap around behind the thrust washer, which can lead to a seal failure.

With a ball-peen hammer, tap the edge of the washer to knock it loose so the fishing line can be removed. When putting it back together, apply a light coating of grease on the splines.

Charlie: I highly recommend doing a visual check every time you run a boat, looking for dings or cracks. Other than that, props don’t need much maintenance.

Why buy Turning Point Propellers?

Charlie: Turning Point Propellers has been around for twenty-five years. They’ve been the fastest-growing boat prop company over the last ten years. They own their facilities and tooling. In their stainless-steel facility, while no two cast stainless steel propellers can be exactly identical compared to props produced using a CNC manufacturing process, Turning Point Propellers has industry leading consistency from propeller to propeller do to their highly automated manufacturing processes. This is one of the things that sets them apart from other propeller manufacturers in the market.

Phil: Even though we have good products, we always try to improve them. We are currently working to enhance props for both pontoon boats and bass boats. We’re also known for our customer service. We answer as many as a hundred calls daily during the summer months. Ultimately, we work hard to get our customers the right props for their boats.

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