Stainless Steel or Aluminum Prop? How to Choose the Ideal Metal for Your Boat’s Propeller
Countless factors go into choosing boat props. They come in all shapes and sizes. Pitch, number of blades and branding are just the beginning. Throw in metal types into the mix and it just spells confusion.
Basic Prop Construction
Real quick: To better grasp the differences and advantages of each type, I'll cover standard prop construction and style. The big three to remember are the number of blades, diameter (blade tip to blade tip) and pitch.
Many prop specs, however, exclude the first number and only list the diameter and pitch. Keep in mind the pitch will play a big factor in the battle of the metals (props, mind you, not metal bands).
Aluminum Boat Props
Aluminum propellers have many advantages and are by far the most plentiful in the freshwater market. You can almost guarantee that for every single steel prop sold, there are 10 aluminum props.
In saltwater, stainless steel is king (but still should be rinsed and washed with a de-salt concentrate after an outing ), but you can say that's due to the bigger horsepower that you see all the time. They come in all the standard styles from three to four-blade props.
Different sizes are available from 2.5 hp outboard motors to 150 hp. For stern drives, they're available for all the different models with the exception of the duo prop models (which exclusively use stainless steel).
In addition, there's a wide selection of aftermarket and OEM props to choose from, both pressed in hub and hubless design.
The Cost of Aluminum Props
Aluminum props are by far more affordable than steel. On average, my customers spend from $160- $220 on aluminum props.
Steel props cost anywhere from $400- $850 to even upwards at $1,500 dollars a pop like this Volvo Penta OEM Duo Stainless Steel Prop (Available on Amazon)!
It's also due to aluminum prop's low cost. If you're still trying to find your boat's perfect prop at your favorite watering hole, if it doesn't work you're not out $400- $600.
I don't have 600 Benjamin's burning a hole in my wallet to experiment on the boat. What about repairs and the cost therein? I can't give prices for every market, but here in Utah, aluminum prop repair's generally in the $80- $120 range. You might already see the problem here.
For not much more money, you can get a new prop. When you can reuse the hub in your old prop, the decision's a no-brainer! I recommend this QuickSilver Flo TORQ II Kit (Available on Amazon) for this switch.
Always carry a spare on the boat! Aluminum props are perfect as spare props without spending the money on stainless steel. Get an aluminum spare prop, at the least. It may save your life.
Life Expectancy of Aluminum Props
An aluminum prop's life expectancy is quite variable. It really boils down to your driving skills. If you can't drive a boat to save your life, you'll eat props like my son eats Halloween candy (which is to say, it doesn't last the week).
If this is you, then stop reading. Your decision is crystal clear: Stick with hubless aluminum props as they're the most economical for your driving style.
Aluminum Prop Application
Your boat's motor is one major factor in the quest for the best prop. For this, I have two questions:
Question 1: What is the horsepower of your motor? If you don't know the horsepower, how many cylinders does it have?
Answer 1: My general rule of thumb is if it is 150 and above in horsepower you need SS. If you are below that or experimenting for optimal performance aluminum is a good choice.
Question 2: Is your gear case "duo prop" (aka has two props)?
Answer 2: If you have a duo prop, the choice is easy. You have to use the OEM recommendations, which are always SS. You're also looking at more expensive props on the market due to the unique nature of duo props. Yes, they do perform superior to standard set-ups, but they come at a price.
There are exceptions, though. The Yamaha Vmax SHO outboards, Evinrude E-tec G2 outboards and Mercury Verado outboards almost always use SS due to the unique high-performance nature of these motors.
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Which Brand of Aluminum Prop Is Best?
The quick answer? The brand you prefer! I know I'm cheating and you're after knowledge, so it comes down to this: I prefer OEM for small outboards 2.5 hp to 40 hp.
With smaller motors, the props are typically inexpensive, making it is easier to just go with OEM (knowing it will work). I don't have to worry it's not going to fit.
Plus, a dealership might have it in stock, so when you're in a pinch, you can get one ASAP.
If you're not in a pinch or want alternatives, here is my reasoning: Solas offers a wide selection. They even have props for older motors you can't seem to find anywhere else. And here's a trade secret a sales rep from Solas told me: Solas builds many OEM props from many big-name brands, especially Evinrude.
So if you want a good prop for less money, Solas is a good route to go. Quicksilver makes excellent props and they're cheap. They also offer various hub kits. If you have a specific brand, chances are you can find a hub kit to fit.
Stainless Steel Boat Props
SS is identical to aluminum when it comes to styles. However, a majority of SS props do not use a hubless design. That means you are stuck with a hub that is pressed in. Or, in other words, Prop A will not work with Motor B.
The Cost of Stainless Steel Props
As mentioned, you're going to pay a pretty penny for a stainless steel prop. The question begged is... why pay the extra money?
In my experience, the typical SS prop repair ranges from $140 - $250 (remember, I'm from Utah, but prop repair prices will vary). Yes, stainless steel is more expensive to repair, but it's also worth the effort compared to aluminum.
You'll repair SS over buying a new one because repairs are hundreds of dollars less than buying new.
Life Expectancy of Stainless Steel Props
SS props have a much longer life expectancy. They're durable and stronger than aluminum props. They also don't experience flexing. Since aluminum is softer than SS, when it's under load and rotating thousands of times a minute, it loses its pitch.
What I mean by that is that the blades under a load will move, which negatively affects your performance. SS holds a more true pitch, which gives you better performance and even better fuel economy.
Think of it this way: Aluminum is like a car with a funny transmission that sometimes slips or shifts hard. SS is like a fine-tuned performance car that shifts effortlessly and doesn't slip when put into gear.
Application of Stainless Steel Props
I don't want to repeat myself, but to recap: If you have big horsepower, a motor that is high performance, a duo prop and/or you know which pitch is right, SS is the way to go.
Which Stainless Steel Prop Brand Is Best?
OEM, Solas and Power Tech (if you've been paying attention, you know that I'm cheating). Solas makes many props for OEM (with a few exceptions).
Power Tech, however, can be a lot less money for SS, which is always appreciated. However, for OEM props, you can't deny they've done the math for optional performance for your model motor.
Pros and Cons for Aluminum and Stainless Steel Props
Wrapping up, I find it's always beneficial to cover the pros and cons when you have a difficult decision.
- Good for testing which prop is optimal for your boat
- If you impact an underwater object, the prop usually fails instead of causing damage to the shaft or seals
- Four blades are available
- Lighter in weight
- If you damage it, you don't feel as guilty
- If you're in short notice for a prop, a dealer will stock more aluminum than SS
- Makes for an affordable spare
- Fragile compare to SS
- Cost of repair can be almost the same price for a new prop
- Not good for higher horsepower motors, or high-performance motors
- Only come painted black so not as fancy looking
- Lower fuel economy
- Do not hold a true pitch as blades flex under pressure
Stainless Steel Pros:
- Better performance
- Better fuel economy
- Blades don't flex
- More durable and more capable to be repaired
- Designed for 150+ outboards, and V-8 I/O's
- It's shiny!
Stainless Steel Cons:
- Impact underwater objects, you can damage seals or prop shaft (albeit, rare)
- Extensive damage repairs can be expensive
- SS props can become back-ordered for months
When choosing the right prop for your boat, there are a few more suggestions. Refer to your owner's manual or contact your nearest dealer for OEM recommendations.
When in doubt, the people who built your motor will know what'll work best. Now, if you're looking at other options, here are the main points:
- Aluminum is affordable and makes a good emergency spare prop.
- Aluminum can determine the right pitch without making expensive mistakes.
- SS gives maximum performance out of your engine, better fuel economy and durability.
- SS is recommended for outboard motors 150 hp and above. For V8 engine, use inboard/outboard.