Most outboards — 90 percent by some estimates — are equipped with three-blade propellers, and most offer strong performance. Yet can you expect better performance from a four-blade prop? The answer is yes — and no — according to experts from some of the major outboard brands.
Three-blade propellers are popular because they tend to offer a performance compromise, a pleasing (or at least satisfactory) blend of acceleration, fuel efficiency, lift and speed, says David Meeler, marine product information manager for Yamaha Outboards.
But if you want to improve acceleration, fuel efficiency or lift, a four-blade might help, Meeler says. “Just be aware that performance gains in one area can mean performance losses in another,” he adds. “It’s all about what’s most important to you.”
Also, before changing props, make sure there are no other factors adversely affecting performance, such as hull fouling, lack of adequate power, or improper weight distribution. Only after you are confident that the boat and power are well-tuned should you then move on to propping.
Define Your Goals
Decide which performance attributes you desire most. The captain of a flats boat, for example, might want to pop up on plane more quickly, and add lift for running in very shallow water. “Often, a four-blade propeller is the ticket,” says Meeler. “The additional blade area grips the water better, allowing for quicker acceleration.”
The greater blade area also lifts the hull more while underway, which minimizes draft. However, the additional drag generated by an extra prop blade can also reduce top speed, Meeler advises.
While speed is important to some saltwater anglers, others seek fuel efficiency and the fishing range that comes with it. “This is where a four-blade prop can really help,” says Dennis Ashley, assistant national sales manager for Honda Marine.
“The extra lift of four-blade props helps keep a relatively heavy center-console boat on plane while traversing rough seas in the mid range, say around 3,000 rpm,” Ashley points out. “That’s far more efficient than slogging along off-plane, and a lot more comfortable and safe than pushing up the speed in heavy seas.”
Also, boats — like people — tend to gain weight as they age, usually as the result of adding fishing accessories such as hardtops, towers, livewells, coolers and other gear over the years. “The propping that worked just fine when the boat was new might not be adequate 10 years later,” Ashley explains. “Four-blade propping might be just what you need to add lift to the older, heavier boat.”
Ventilation — the tendency of the blades to lose their “bite” — often occurs when props are immersed in aerated water, such as the wake of a stepped-hull boat. On other boats, aeration can be unintentional, caused by poorly positioned water intakes or large through-hull transducers.
A four-blade is less likely to ventilate in aerated water, simply because it has more blades to grab the water. That’s why you see some stepped hulls equipped with these props.
Four-blades can resolve other ventilation issues. If a helmsman elevates the jack plate on a bay boat too high, the prop tends to lose its bite and ventilates. The grip of a four-blade allows a bay-boat captain to maximize the height at which he can run the outboard, and cross flats that might not be navigable with a three-blade prop.
Assuming you want to improve some aspect of performance, your dealer and his service department can help you make a decision, Ashley says. “But at the same time, it’s important to communicate your expectations so the dealer can recommend props to achieve your performance goals.”
Another good source of guidance includes outboard-company websites. The propeller section of yamahaoutboards.com, for example, contains a wealth of information, including a five-step section on picking a propeller, back issues of Yamaha’s Prop Shop newsletters, and performance bulletins on a wide range of boat/motor/propeller combinations.
The Prop Selector Tool at marine.honda.com and the Prop Selector at mercurymarine.com also offer five-step interactive sections that calculate and recommend the most appropriate props based on your boat type, performance goals and outboard power.
Seeking the real-world experience of owners who run your boat model can also prove helpful, says Dave Greenwood, product planning manager for Suzuki Marine. “Look for boats at the marina or launch ramp and ask the captains about the props they are running,” Greenwood suggests. Try to pare down the field to three or four candidates.
Test and Evaluate
The next step is to procure the propellers for testing, and again, you can often work with your dealer on this. “Mercury Marine dealers have access to demo propellers, allowing a consumer to ‘try before you buy,’” says Jared Reichenberger, brand manager for Mercury Propellers.
Other dealers have rental programs. Most of the time, however, you need to purchase test props from a dealer. (That’s when you will find that four blades cost more than three.) “Just make sure there’s an understanding that you plan to return most of them undamaged for a refund after testing,” says Greenwood.
It is important to test each prop under the same conditions, says Meeler. “A simple variable such as warming air temperatures can affect speed as much as 5 percent,” he explains. Also, make sure the water conditions are the same. For the sake of ease, try to test on flat water.
“Make sure the boat is fueled and loaded as if you were going fishing. That means full of ice and tackle, full livewells and full crew, if possible,” Ashley advises.
It’s also important to use the same criteria in each prop test, and to make this simple, Yamaha offers a detailed Propeller Performance Evaluation form that you can obtain from an authorized Yamaha Outboard dealer. Use the form to record performance data for later evaluation.
You also need some test gear, including a GPS (found aboard most fishing boats) for recording boat speed, a stopwatch (like the one on a smartphone) for timing acceleration, a fuel-flow meter (found on many fishing boats) for determining fuel efficiency, and a tachometer.
Though not measured directly, lift is the inverse of minimum planing speed — the lower the minimum planing speed, the greater the lift. Make sure you test in a marine environment rather than your local lake, as salt water has greater buoyancy than fresh water.
Ultimately, these tools, resources and guidelines — plus some on-water testing — can help lead you to the propeller, be it three- or four-blade, that enhances the performance characteristics you desire most in your saltwater fishing boat.
Diameter and Pitch
Two key measurements of a prop are diameter and pitch. Pitch is the theoretical distance (e.g., 19 inches) a propeller will move a boat with one revolution of the prop shaft. Generally speaking, the diameter of a four-blade prop is smaller than that of a three-blade prop with the same pitch, says Jared Reichenberger, brand manager for Mercury Propellers. This helps a four-blade spin up quickly and allows the motor to rev as high as it would with a three-blade of comparable pitch, Reichenberger points out. Nearly all saltwater props for outboards are made from stainless steel.