Pick the Best Propeller for Top Boat Performance

If you want your boat to deliver more tomorrow than it does today, it’s time to enter the spin zone, because getting your propeller dialed in is the number one way to attain the performance you’re looking for. And if you haven’t tried swapping props in the past, chances are the one you’ve been using is no longer in optimal condition and is robbing you of fishing time and money at the gas pump.

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IMPORTANCE OF PROP SELECTION

Why don’t all boats come with the perfect prop in the first place? Because the ideal choice depends on a number of variables, including the hull’s design and dimensions, the weight of the boat and its load, and the performance aspects on which you place a premium. Top speed, fuel efficiency, hole-shot quickness and the ability to get on and stay on plane can all be affected by your prop selection.

In most cases, boat manufacturers ship new boats with a stock prop that provides a happy medium for different performance attributes. But they can’t account for how you’ll load your boat, or where and how you’ll run it. They also don’t know which characteristics are most important to you, and they can’t water test and tweak each individual boat after it’s left the lot. Achieving peak performance, therefore, is left up to the vessel’s new owner.

PROPELLER BASICS

Before delving into the ins and outs of proper propping, let’s touch on the three critical factors to consider: propeller material, number of blades, and size.

Most propellers on today’s outboard-powered boats are made from either stainless steel or aluminum. As a rule, stainless-steel props yield better performance than their aluminum counterparts because the blades flex less. Swap from aluminum to stainless, and you’re bound to see your speed increase by a couple of miles per hour or more. But stainless-steel is more expensive, so the motors on many of the smaller rigs sold to price-conscious buyers come with an aluminum prop.

Propellers designed for outboards come in 3-, 4- and 5-blade configurations. While 3-bladed models are most widely used, more blades increase a prop’s bite on the water and often help overcome or lessen certain performance troubles. If your boat struggles to get on plane, won’t stay on plane at slow speeds or has issues with ventilation (when the propeller sucks air instead of water, reducing its contact with the water and diminishing thrust), switching to a 4-bladed prop can be a big help. However, the additional drag created by the extra blade is likely to trim a few mph off your top-end speed. It could also slow your boat’s hole shot, something to keep in mind, particularly if you run a flats or bay boat and must frequently jump on plane quickly in shallow water.

Picking the right prop size is where things can get tricky, because size has two components: diameter and pitch. The prop’s diameter is exactly what it sounds like. Too large a diameter will create too much drag and decrease acceleration. Too small a diameter will increase the rpm yet lack the proper thrust to jump on plane and accelerate quickly. But don’t fret, you’ll rarely have to worry about picking a prop with the wrong diameter because recommendations from outboard and boat manufacturers are generally spot on. Pitch, however, is a bit tougher to wrap your head around.

Pitch is a theoretical measurement of the distance a propeller would travel forth if it were turning through a solid material (think of a screw pushing further into lumber with each complete rotation). Adding one inch of pitch could increase your top-end speed, but it will also result in slower acceleration. You can expect the opposite result if you go down in pitch. While a lower pitch will increase the rpm, going too low will cause a motor to overrev and could result in serious damage.

We should also mention that there are some highly-specialized propellers—designed for specific applications—that don’t necessarily fit the aforementioned descriptions. For example, Suzuki Marine’s DF350AMD and DF300BMD outboards (suzukimarine.com) are fit with contra-rotating twin propellers designed for said engines. That’s two propellers that turn in opposite directions on the same shaft to seriously boost their bite, while spreading the torque evenly over each prop. It’s an incredibly effective system for getting heavy boats up on plane quickly while still providing hat-stripping acceleration.

SWAPPING PROPS

Deciding which material and number of blades will work best for your needs may be pretty straightforward but, when you get to sizing the prop, it’s crucial to ensure the engine’s rpm remain within the manufacturer’s recommended range when running at wide-open throttle. This assures your outboard will produce the most power possible without pushing beyond its design’s parameters.

You’ll gain about 200 rpm with every inch you drop in pitch and lose 200 rpm with every inch of pitch increase. Generally, it takes trying out multiple props of different pitches to achieve your target rpm range, and this is where your personal priorities come into play. If maximum top-end speed is your main concern, you’ll want the highest pitch prop possible. But let’s say you often shove off the dock with a full crew and lots of gear, and you regularly fish in heavy seas. You might find it more important to mush along at minimal planing speeds so you don’t get beat up. In that case, you might be willing to sacrifice top-end mph and opt for a lower pitch prop that will get you on and stay on plane at slower speeds.

When it comes to selecting a propeller, the recommendation of the outboard manufacturer or a savvy boat dealer is likely to be as good or better than your initial guess. But there’s really only one way to find the perfect prop: real-world use. If you want to make sure that you’re spinning the ideal propeller for your needs, it’s time to start swapping and testing props and see how your boat performs with each.

PITCH PERFECT

• Subtle nuances can make a world of difference.

A boat propeller’s pitch is achieved through the size, shape and angle of its blades. The blades are designed with a twisted or curved profile that causes them to push against the water and translate rotation into forward motion. How much water they push with every full turn directly affects rpm, acceleration and overall efficiency.

ONLINE ADVICE

• Instead of just guessing, turn to an online prop finder as a starting point.

When you have no idea what prop is most appropriate, using an online “prop finder” can be a great place to start. Many are available from outboard manufacturers and propeller shops. Mercury Marine (mercurymarine.com), Yamaha Marine (yamahaoutboards.com), Solas (solas.com) and West Marine (westmarine.com) are among the best. They help narrow your prop search by letting you choose from the provide options in boat type and size, engine make and model, and additional variables to select a propeller that should fit the basic parameters and at least come close to meeting your desired performance requirements.

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• This article was featured in the June-July issue of Game & Fish magazine. Click to subscribe

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