Thursday, April 9, 2009

Propellers: Stainless or Aluminum

The two main materials used for recreational boats are either aluminum or stainless steel. While they can be used interchangeably, they do have specific purposes. Depending on the type of boat you have and what you want to do with your boat you will need to decide which material will work best for you.

Both types of material have advantages and disadvantages and some engines will really only perform well with one material or the other. A small horsepower engine (a 4cyl. sterndrive, for example) really doesn’t create enough torque to spin a SS prop as it weighs considerably more than an aluminum prop. The potential gains of the SS are negated by the fact that the engine can’t spin the prop fast enough. On the other hand, a big, high horsepower monster engine will all but require the use of a SS prop to be able to handle the high torque that the engine creates. The blades of an aluminum prop will actually deflect under the demands of engine’s higher torque, thereby rendering it much less efficient – possibly useless.

An aluminum prop has a lower initial cost and is usually less expensive to repair. However, it can also be damaged easier. While a SS prop is more expensive to purchase, it has a much longer usable life. An aluminum prop can be damaged quite easily by debris in the water or certainly by hitting the bottom; a stainless prop will more than likely chew right through sticks and other debris and not even think twice about it. It’s even possible for a SS prop to survive a light hit against rocks. A benefit that most boaters will appreciate when using a SS prop is faster acceleration, improved throttle response, more pulling power and increased fuel economy. But again, these benefits can only be realized when the engine has enough power to spin the prop efficiently.

Hitting something underwater brings up another point. What about the “shockwave” that is created by the hit and sent up through the driveshaft to your engine? Because an aluminum prop is made of softer material it will take the brunt of the hit, although it more than likely will be damaged beyond use and possibly beyond repair. A SS prop may very well survive the hit unscathed, but could send that shockwave up to your engine. However, most propellers have an internal “shock absorber” to help with this.

In the end, talking to a professional or using something like Mercury Marine’s online Propeller Selector will more than likely help to make your decision easier.

One last note: If your prop has any signs of damage – rough edges, bent blades, chips/gouges, etc. – get it repaired ASAP. Even just the tiniest amount of damage will cause the prop to be out of balance and when it is spun at thousands of RPM’s that will translate into “bad vibrations” being sent to your engine (the “shock absorber” will be of no help in this situation). Call or visit your local marine dealer or repair shop and ask about a propeller repair service.

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