Choosing the best pitch and diameter propeller for your boat is tough enough (read Outboard Expert: The Right Propeller, to find out how it’s done), but to make things even more complex you’ll also have to choose the best material: aluminum or stainless-steel. And yes, it does matter. Performance, efficiency, reliability, and overall cost are all factors that come to bear, and making the wrong choice can have a pretty dramatic effect on your boating experience. So, how will you decide? Let’s find out.
ALUMINUM PROPELLER PRO – They’re less expensive, often to the tune of hundreds of dollars. In fact, in many cases the aluminum version will be half the cost.
ALUMINUM PROPELLER CON – Aluminum just isn’t all that tough when it comes to physical contact, so an aluminum prop regularly exposed to brushes with sandbars, small rocks, or even muddy bottoms will get dinged, damaged, and worn down in no time.
STAINLESS-STEEL PROPELLER PRO – Stainless-steel propellers are far more durable. They will last virtually forever, unless you strike something hard enough to cause damage. So you could end up buying two or three aluminum “wheels” when one made of stainless-steel would have lasted at least as long.
STAINLESS-STEEL PROPELLER CON – In some cases, that extra strength can be problematic. If you strike something hard those blades simply won’t give, and the forces get transmitted right into the lower unit. If the striking is hard enough, the damage that results could require costly repairs—far more costly than just buying a new propeller.
ALUMINUM PROPELLER PRO – There’s a huge range of aluminum props out there, for all but the largest horsepower ranges. No matter what shape or type of boat you have, it’s virtually guaranteed there’s an aluminum propeller made to be the proper fit. Wider bladed models designed for pontoon boats, four-bladed models designed to improve hole-shot or maximize trim on bass boats—no matter how specialized you get, there’s probably a model out there that fits the bill.
ALUMINUM PROPELLER CON – There’s one big exception: if you need a vented propeller, you’re out of luck. Vented props have holes behind the blade which introduce bubbles to the blades, adding turbulence and allowing the propeller to spin a bit faster. It’s a helpful feature for boats that may have difficulty getting onto plane, since it allows the engine to turn at higher RPMs as power is applied.
STAINLESS-STEEL PROPELLER PRO – Stainless props provide better performance, because their blades flex less. In fact, it’s quite common for a stainless-steel propeller (all other things being equal) to out-perform an aluminum propeller by as much as five MPH at top-end, and two to three MPH at cruising speeds.
STAINLESS-STEEL PROPELLER CON – Historically, better performance was the main selling-point for stainless-steel as the material of choice. It should be noted, however, that with new alloys and casting techniques, the difference isn’t as dramatic today. In fact, a well designed and built aluminum propeller can, in some cases, out-perform an average or dated stainless-steel design.
Now it’s time to make a choice: which will it be, aluminum or stainless steel? To decide what's right for you, apply each of these pros and cons to where and how you use your boat. Obviously, if you’re pinching pennies, aluminum might be the only option. But if your propeller regularly rubs sand or mud, stainless will be a better buy in the long run. Unless, that is, you also regularly ram hard objects. In that case, an aluminum propeller is the sacrificial better bet. Except, possibly, if you carry excellent insurance... or if you need a vented prop. Then consider the impact on performance, and how big a difference it makes on your specific rig.
Score each factor by level of importance on a scale of one to 10, record your results, and then do the math. Whew! Which one worked better for you and your boat?
If you're still on the fence, try running your boat with a prop of each type and compare the results. To find out how to perform an accurate test, read Finding The Right Propeller, another article by the Outboard Expert, where our propeller-spinning tech-head Charles Plueddeman walks you through an on-the-water comparison of four different propeller options for a Lund 1700 Fisherman with a 115 HP Mercury outboard engine.
If you haven’t changed a propeller before, before you get started with your own test watch our How to Change a Boat Propeller video.