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Author Topic:   Effect of Material on Propeller Pitch Rating
rtlo posted 09-23-2004 08:45 PM ET (US)   Profile for rtlo   Send Email to rtlo  
I have a PRO TEAM 175 BASS TRACKER with a Mercury 50-HP 2-stroke with tilt/trim. I have the factory rigged aluminum prop that is a 10-3/8 by 14 pitch. The boat runs 31-32 MPH @ 5200-RPM. I ordered a SS Rapture prop for it and the people at Rapture told me because of the performance of the prop I needed to go down two pitch sizes to obtain or gain on whatI have now.

Does any of this advice seem correct?

I ordered a 10-1/2 by 12. Thanks

jimh posted 09-23-2004 08:57 PM ET (US)     Profile for jimh  Send Email to jimh     
Propeller performance as a function of propeller material is generally not affected by the brand of boat, so it works the same on a Boston Whaler as it does on a PRO TEAM 175 BASS TRACKER.

Generally at horsepower below about 100-HP, and at boat speeds below about 35-40 MPH, I don't think you will see an enormous difference between the performance of an aluminum propeller and a stainless steel propeller.

For some thoughts about the differences that material can play in the performance of a propeller, please see:

Propeller Basics: Part 2
Propeller Materials

Your other question is more to this point:

Do the people who make and sell propellers know anything about how they work, or should the random advice from internet sites be given more weight?

In general, the people who make and sell propellers who actually do know how they work are usually the people who have been in the propeller business for some time and have been successful at it. So I would tend to give more weight to their advice than to the random reply from an internet web-based discussion forum.

The particular pitch number that a manufacturer puts on a propeller is not driven by or regulated by any particular standard, so it is possible that a propeller from one maker which carries a pitch of "17" might be more difficult for an engine to turn than a propeller from another manufacturer which is also rated as a "17".

The outboard motor cannot see what the rating stamped on the propeller is, so it just turns them as fast as it can, and in so doing the engine really sorts out what propeller is what. In some cases propellers with lower pitch numbers given to them by their makers may not be able to be turned by an engine as fast as another propeller from another maker with a higher number for its rated pitch. In these cases the people making the propeller usually know this tendency and can offer you some advice.

This is to say that not all propellers of a particular pitch are equal in the load they place on the engine, and the engine will gladly show this to you by the maximum speed at which it will run when the propeller is in use.

jimh posted 09-23-2004 09:03 PM ET (US)     Profile for jimh  Send Email to jimh     
[Removed this article from a three year old thread where it was appended recently.]

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