Choosing a Propeller

The right prop maximizes performance

The right propeller on an outboard
Picking the ideal prop requires you to test a few, taking into account differences in diameter, pitch, rake and cup.Courtesy Yamaha

The recent flurry of new outboards is giving anglers even more choices when rigging a new boat or repowering an existing one. While hull shape, weight distribution, engine mounting height, and often accessories like a jack plate play a role in the boat’s performance, nothing is more important than the right propeller for wringing every bit of horsepower out of a motor and achieving the desired ride. Outboard manufacturers realize this and—along with launching faster, more efficient and technologically advanced motors—are producing new prop options as well.

Mercury recommends a series of tuned propellers to match the new high-performance Mercury Racing 450R outboard launched earlier this summer. This ­4.6-liter V-8 four-stroke with an available 5.44 HD gear case is designed to run with either the Bravo I FS, Enertia Eco XP or Rev 4 XP prop.

Evinrude has launched two new prop lines with a range of ­diameters and pitches to meet the ­performance requirements of its new inline three-cylinder E-Tecs. The three-blade RX3 and four-blade RX4, both ­stainless-steel props, are designed to match the power curve of the new G2 engines, with strong acceleration and midrange fuel economy.

The RX props feature the VVB venting capability, where a simple ­adjustment can loosen a hub valve to introduce more exhaust. This allows the prop to break loose to accelerate to quicker planing speeds.

“The RX3 is optimal for ­general cruise and boat control,” explains Larry Koschak, Evinrude’s accessories manager. “It will maintain a bite without breaking loose. RX4 props are better for rough water. And both offer excellent fuel economy by allowing cruising speeds at more efficient rpm.”

Yamaha matched its powerful (425 hp) 5.6L V-8 XTO Offshore outboards with the new XTO propellers. Mark Kennedy, an avid tournament angler from Mobile, Alabama, just took delivery of his new Yellowfin 39 rigged with triple XTOs and the companion props.

“The XTO props are all-purpose, large-­diameter and heavy-duty, designed more for cruising applications rather than high-performance hulls. They are the only ones available that will fit the big shafts of these new engines right now,” Kennedy says. “Yamaha is working on adding ­options in the future. In the meantime, I pulled mine and had Tillman’s Propeller Service fine-tune them. The props were balanced and had more progression added to the leading edges, plus more cup to the tips. So now they bite better and don’t slip.”

Kennedy went with 16⅛-inch-­diameter, 23-inch-pitch props on all three engines. His previous Yellowfins, powered by different Yamahas, were a mixed setup. He ran four-blade props on the outer motors and a three-blade on the center to handle the extra load.

“The tuneup on the XTOs made a big difference,” he says. “It was really a pleasant surprise. I picked up 2 miles per hour at wide-open throttle, and increased my fuel efficiency by 15 percent at cruising speed. When you’re running long distances offshore, that is critical.”

Suzuki, meanwhile, turned its ­innovative Watergrip props—standard on DF350 motors—into a series that fits all DF150 through DF300AP (except DF150T and DF175T) outboards, with additional models in the works. Watergrip props feature an octagonal rubber bushing that will turn like a ratchet and slip slightly when the prop impacts a hard object, protecting the outboard’s drivetrain, yet still providing the friction needed for high-speed operation. “These new props are designed to grip the water better, and the new bushing makes them more durable and ­easier for our customers to use,” says Gus Blakely, Suzuki Marine’s vice ­president of sales.

Sharrow Engineering’s rotary props are perhaps the most intriguing propeller development. They haven’t hit the recreational outboard market just yet, but extensive testing has shown appreciable performance characteristics. They’ve been in the works for ­seven years and are built using computer-­assisted design and 3D additive technology, and their design evolved from super-quiet drone blades developed for the military and other applications. The Sharrow props will be built in a range of sizes, with universal hubs.

“Because of the way the blade elements are connected via the outermost region of the loop, and the fact that our ‘tip’ section doesn’t get as thin as a conventional propeller, the entire structure is stronger, more rigid, and less prone to failure,” CEO Greg Sharrow explains. “Typically, the Sharrow propeller produces a more uniform downstream thrust field as a result of reduced tip vortex losses, less cavitation, and more balanced blade loading. This results in a smoother ride, more responsive steering, and better ­fuel economy overall from low-end to top-end speeds.”

Even with the advances in propeller design and performance, every boat and every application is different. Factory suggestions and performance bulletins are good starting points for ­choosing the right props, but optimizing hull performance to match fishing styles and conditions often requires some ­experimentation.

Pitch is the theoretical forward progress of a prop during one revolution. The right combination of prop diameter and pitch produces the ideal rpm range.

Rake is a prop blade's face angle relative to the hub. A higher degree of rake increases bow lift.

Cup is the curve in the trailing edge of a prop blade that affects boat trim, fuel burn and overall performance.

Prop-Blade Puzzle

Yamaha XTO Propeller
Yamaha XTO prop (three-blade)Courtesy Yamaha
Evinrude RX4 Propeller
Evinrude RX4 prop (four-blade)Courtesy Evinrude
Mercury High Five Propeller
Mercury High Five prop (five-blade)Courtesy Mercury

Three-blade props afford the desired performance for a wide range of boats and conditions, but more blades often help improve hole shot, minimize cavitation and prop slip on takeoffs and turns, and maintain acceleration in situations when part of the prop breaks the surface. Some flats skiffs and bay boats, especially those with a transom step or pocket, or a jack plate for shallow running, benefit from a four-blade prop. High-performance boats often opt for five-blade props to increase top speed.