Add Some Spin to Your Boat’s Performance

Propellers are one of contributing factors to achieving top-end speeds and optimal handling. Upgrading to a new prop just might add that punch your cruiser, runabout or pontoon needs.

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Words by Steve Fennell

Performance on any type of boat starts from the bottom up. The hull design, number of horses on the transom, load weight and even balance all play an integral role to ensure the utmost power and continued acceleration out of the hole.

While props are a fraction of the size compared to many other components on an engine, they are one of the main parts that contribute to performance regardless of the size, model and style of your boat. You may want to speak to a qualified technician to truly understand how props transfer that extra punch to your boat, understanding the essentials - and using a little common sense - is all that’s required to know when to replace or upgrade it.

Engine and boat manufacturers spend a great deal of time matching the correct propeller with a particular hull design and engine. However, there are several reasons to replace a prop to better suit your boating lifestyle and you just might be surprised by the results.

Determine Load Weight

If you have ever been on a boat with a heavy load and it seems to take forever to get on plane, look at the size of the prop on the lower unit or drive. Heavier loads are often overlooked as one of the main causes of sluggish planing times, slower cruising speeds, and increased fuel consumption.

“Boaters will often buy a 6 m (20 ft) runabout with a 3.0 L sterndrive or 150 hp outboard for their family and it will run great enjoying all kinds of activities,” says Gary Diehl, Propeller Brand Manager for Mercury Marine. “But after a few seasons, the kids start growing or they bring along their friends, and the onboard weight unknowingly increases, which can make the boat difficult to plane and feel underpowered. People may think they need a new boat or a larger engine but re-propping can often be a simple solution for better performance.”

Diehl continued to explain that opting for a new prop with a lower pitch is a great start to solving the problem. It can often bring back a lot of the performance when the boat constantly has heavy loads.

For example, if your boat was running a 19” pitch prop, choosing the same prop model like a Mercury Enertia with a 17” pitch will help the engine achieve its maximum RPM at slower speeds. As a result, it will provide quicker holeshots and planing times (depending on the engine, boat model and application). However, keep in mind that some of the top-end speed may be compromised.

The exact opposite may also be experienced. For instance, in the event your kids are no longer interested in tubing or there are only commonly two adults on board, you may experience too low of a pitch. Some of the signs of this include over-revving, the engine may be noisier, or you’ll notice reduced fuel economy. A common solution is to choose a prop with a higher pitch (e.g. from 17” to 19” or even to 21”).

“Changing the prop model and pitch can vary so much based on the type of boat and engine,” says Diehl. “That’s why many companies like Mercury offer such a high volume of propellers in different models and for various applications, including vast pitch ranges from 11 to the low 20s for most models. There are even higher pitches for offshore performance boats. If you’re considering a prop for a 6 m (20 ft) runabout, the prop should generally be in the 17,” 19,” or 21” pitch range.”

Three-Blade vs. Four-Blade Propellers

With a variety of propeller sizes on the market, three- or four-bladed props are popular, and it’s important to understand the differences to achieve top performance and speed for the type of boating you enjoy.

Three-blade propellers are most commonly used on recreational boats such as pontoons and runabouts as they are very efficient and offer faster top-end speeds for engines under 200 hp. However, one of the advantages of a four-blade propeller, however, is there’s an extra blade in the water propelling the boat (rather than just one with a three-bladed prop) at any given moment. Since they cover more surface area below the water, there’s less chance of ventilation during sharp turns or when an engine is mounted higher on the transom or it’s trimmed too high.

“A four-blade prop will have better acceleration, improved performance, and stay hooked when you’re cornering,” says Diehl. “But the same four-blade prop may not perform as well on different boats. That’s another reason why there are several choices available.”

Stainless vs Aluminum

Handling higher horsepower applications, hitting underwater obstructions, and cost are just some of the criteria when choosing between a stainless steel and an aluminum prop.

Okanagan Lake is extremely deep but select areas (or other bodies of water you may visit in the BC interior) typically are not. One of the main selling features of stainless steel props is their metal properties and precisely-engineered thin blades, which not only provide strength but more tolerance to stress (over an aluminum prop) when they hit an underwater obstruction.

Despite this advantage, if you unintentionally and routinely hit the lake bottom while trolling shallow water or enjoying other activities, the cost to replace or repair a damaged stainless steel prop is twice - or even three times - the cost of an aluminum one.

Its thinner blades are also designed to create less drag and combined with the fact that they won’t flex,  you’ll appreciate the benefits of higher top-end speeds, better fuel economy and range. Plus, manufacturers and dealers strongly recommend using a stainless steel prop for engines more than 200 hp to achieve the utmost power and performance from the engine.

Some of the advantages of aluminum props - commonly used for engines less than 175 hp - is they cost from approximately $200 to $300 and have thick blades to prevent flexing. They are also light in weight while still providing optimal performance.

Signs of a Damaged Prop

Here are a few key ways to determine that you may need to replace your prop or at the very least, have it repaired by your local marine shop:

  • Bent Blades, Dings, or Cracks

You should consider a new prop if one of the blades (or all of them) is chipped or damaged on more than 10 to 15 percent of the blade surface. Even tiny cracks can worsen over time. The sooner you see a crack or ding, the easier it is to repair.

  • Wear and Tear

Fading matte surfaces and pointed or blunt edges on the side of the blade indicate excessive wear, which can result in higher revving and less fuel efficiency. To determine the amount of wear to the blades simply compare them to the original diameter.

  • You Hit a Rock or Other Unforgiving Surface

This happens to the most experienced boaters and whether you hit a rock, stump, or other underwater obstruction, the damage can be extensive and ruin your prop(s). Blade(s) will often be bent out of shape and you’ll notice a lack of performance.

“If you know you recently hit the bottom or hard underwater structure and the performance has changed or there is excessive vibration, the prop is likely severely damaged,” says Diehl. “It may only be the prop that took the impact but it’s always for the best to have it repaired or replaced much sooner than later.”