Stainless Steel vs. Aluminum Propellers

It’s an age-old question: should I use a stainless steel propeller or an aluminum propeller for my boat? There are merits to both, but the best way to get the most out of your outboard is to match the prop material to the type of outboard you have and the conditions you run it in. 

The simplest way to decide is to match your replacement propeller to your outboard’s horsepower. Here are the differences between aluminum and stainless steel boat propellers.

What’s the Difference Between Aluminum and Stainless Steel Props?

The biggest differences between the two are the weight and the stiffness of the prop, and that’s where the horsepower comes in. A good rule of thumb is that if your outboard pushes 150 horsepower or less, aluminum might be the best option. Higher horsepower motors can actually spin an aluminum prop with enough torque that the prop will flex in the water, which in effect lowers your ratio and can cut the speed of the boat.

On the other hand, a heavier stainless steel prop on a smaller engine presents its own problems. The heavier prop on the smaller outboard can actually sap a lot of power from the motor just to turn the prop, which can cut the motor’s efficiency.

Advantages of Stainless Steel Props

Another consideration when sizing up stainless steel vs aluminum props is where you’re going to be running your boat. Stainless steel propellers offer more rigidity for high-horsepower motors, and they’re also more durable. 

If you’re running in shallow water where there’s a risk of hitting something with the prop, you’ll want to have something more robust. Stainless steel fits the bill. However, there’s one more thing you’ll want on that setup: a replaceable insert. That way, if you hit something, it’ll damage the insert and hopefully not the prop or the output shaft.

Advantages of Aluminum Props

One big advantage of aluminum propellers is the price. An aluminum prop can cost a fraction of what a stainless prop costs, but there’s a catch: the prop isn’t as strong, which leads to other issues downstream.

Aluminum propellers bend at high horsepower, which cuts your speed. And because aluminum isn’t as strong as steel, the manufacturers compensate by making the blades on the prop thicker. That leads to more drag, which also slows your boat down. If the aluminum propeller takes a strike, it could tear the blade, which leads to either replacing the prop or finding a talented repair shop to mold it back into shape.

Choosing Between Aluminum and Stainless Steel Propellers

So how should you decide between one and the other? There’s no right answer, only a series of tradeoffs you’ll need to weigh as you consider the impact each prop will have on your boat’s performance … and your wallet. 

Ask yourself the following questions when choosing between stainless steel and aluminum propellers:

• How are you using your boat? 
• What environment (deep or shallow water) will you be in?
• What performance level are you looking for?
• How much do you want to spend?

For some, an aluminum prop will do just fine, even with the reduction in performance. Plus with the affordability of aluminum, you can buy two so you can have a spare and probably still not touch the cost of one stainless steel prop. However, if you’re pushing with a lot of horsepower in a high-performance environment, you should definitely go with stainless steel.

Another important decision to make when choosing a propeller besides the material it’s made of is how many blades you want the prop to have. 3 blades? 4 blades? Watch the video above to learn the differences between 3-blade and 4-blade propellers.