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prop rake measurement

Old 08-24-2022, 10:15 PM
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Question prop rake measurement

Am I measuring this right ?

Mercury is supposed to be 15* so even with a angle meter app it`s still 15*
The other seems to be 12*






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Old 08-25-2022, 07:14 AM
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That is how I measured mine.
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Old 01-21-2023, 07:07 AM
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You are on a different level than me here so keep that in mind while reading my questions.
Are these new or have you run them already?
If you ran them was there a difference in rpm?
Did all of the blades of each prop match each other?
This may have been answered by the results of a previous question but what made you check in the first place.
Thanks
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Old 01-22-2023, 05:09 PM
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Not new, at $12k/set new I`m in the used market.
Not sure if there was a question in there but I have cleaver props, it`s not going to be relevant to your bravo stuff.



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Old 01-23-2023, 07:54 AM
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Wow!!! Very Nice!!! I remember a photo years ago I think in "Powerboat Magazine" with the basically the same pic.
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Old 01-25-2023, 09:36 AM
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Originally Posted by ICDEDPPL
Am I measuring this right ?

Mercury is supposed to be 15* so even with a angle meter app it`s still 15*
The other seems to be 12*




I don't think you are measuring correctly. Look at your hub reference point in the first picture. It is elevated above / past the trailing edge of the blade altering your measurement as compared to the lower picture. Imagine the hub shaft extended out another three inches. Your rake measurement would be negative based on your measuring method. This obviously would not be correct as hub length has no bearing on prop rake.

I believe prop rake is measured from mid-chord at the root (hub) extending to the tip and measured from the prop rotational axis. This gets difficult to measure with multiple compound curves associated with many props.
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Old 01-25-2023, 10:54 AM
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Originally Posted by Trash
I don't think you are measuring correctly. Look at your hub reference point in the first picture. It is elevated above / past the trailing edge of the blade altering your measurement as compared to the lower picture. Imagine the hub shaft extended out another three inches. Your rake measurement would be negative based on your measuring method. This obviously would not be correct as hub length has no bearing on prop rake.

I believe prop rake is measured from mid-chord at the root (hub) extending to the tip and measured from the prop rotational axis. This gets difficult to measure with multiple compound curves associated with many props.
Trash, Dan,

I also think these angles should be measured from the C/L of the shaft bore, not the rear face of the hub. We would all hope that face would be square to the bore, but there's no guarantee it will be.

Thanks. Brad.
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Old 01-26-2023, 08:03 AM
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I was always told on a cleaver prop the rake was a measurement of the trailing edge of the prop in relation to the hub surface

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Old 01-26-2023, 12:09 PM
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Agreee ^^^
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Old 01-26-2023, 01:27 PM
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Originally Posted by green lightning
I was always told on a cleaver prop the rake was a measurement of the trailing edge of the prop in relation to the hub surface
Dan,

Keep in mind that, when they say, "differs from perpendicular", they are referring to a line perpendicular to the prop SHAFT. The problem you have is that you are trying to measure the angle of a line from a relatively short reference area (the hub). On a prop with an even number of blades, this will be particularly difficult, as the blade opposite will interfere with the resting of any gage longer than the diameter of the rear hub face. You obviously have 5-blade props, so that's not an issue, but you still have a fairly short reference plane to measure from, assuming that surface is perpendicular to the shaft. It would serve you well to find or have made a dummy shaft that fits the bore in your props that you can measure your rake angles from. Remember, the prop is rotating around the shaft, not the rear face of the hub.

In my world of precision machining, I have to eliminate as many sources of error as possible. These habits are hard to shake for me.

Thanks. Brad.
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