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prop rake measurement

Old 01-04-2024, 08:35 AM
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Originally Posted by Tartilla
I assumed from the definition of rake, that the middle of the blade at the root, the angle to the prop tips.

With cleaver style props, it seems to be a little different, and uses the rear flat portion of the blades as the Rake Angle.

Using tHe shaft as the zero point, vs the rear hub surface that mau not be cut square.to the bore.

My '90s Rollas only have about 10° rake. You can see they have less of an angle. Hoping they have enough bow lift.
Tartilla,

The trailing edge of the working face is all that matters. Anything "behind" that is simply there to materially support the working face.

For what it's worth, adding rake just enables additional rendering of thrust from the water as its being forced rearward and slung outward, where it would just be cast off without it. Essentially, you're just adding blade where there's water to wring thrust from. It consumes additional energy to do so, and also changes the lift characteristics of the blade, as well, so it's not always a feasible feature to implement.

Thanks. Brad.
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Old 01-04-2024, 11:56 AM
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Originally Posted by Tartilla
Great point. Using a few different blades should have different angles if the rear hub face is not square to bore.
If all the blades are the same, you would hope on these expensive of props they would be.

On bravo style props everyone I have ever had worked on the blades have never been the same.
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Old 01-04-2024, 12:18 PM
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Originally Posted by Wildman_grafix
If all the blades are the same, you would hope on these expensive of props they would be.

On bravo style props everyone I have ever had worked on the blades have never been the same.
Wildman,

I don't disagree at all, but, as a MFR, it's not a shocker to me at all. A Bravo is $800. A Herring is $8000. We can buy six or eight labbed, matched blade Bravos for the cost of ONE Herring. Bravos are cast and hand finished. There's GONNA be variances. What would guys like Brett do with their time otherwise, right?

Thanks. Brad.
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Old 01-04-2024, 01:12 PM
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Originally Posted by Brad Christy
Wildman,

I don't disagree at all, but, as a MFR, it's not a shocker to me at all. A Bravo is $800. A Herring is $8000. We can buy six or eight labbed, matched blade Bravos for the cost of ONE Herring. Bravos are cast and hand finished. There's GONNA be variances. What would guys like Brett do with their time otherwise, right?

Thanks. Brad.
Exactly, at least you would hope. Since I am not a buyer of 8K props I do not know, lol.
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Old 01-04-2024, 07:15 PM
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I get that and wasn’t really even considering that.

My point/question is, based on descriptions above, if I cut/change the angle of the trailing edge of the blades, this should change rake correct?

On variability of “as delivered” wheels, always depends on where from.

I went w/a buddy to pick up his, as delivered 30” Cleavers from his trusted prop shop.

According to his guy, I was front and center, there was +/- 3” in pitch.

These we’re from a west coast guy w/a known name and validated what we all thought.


Originally Posted by Brad Christy
Gary,

Since the prop is rotating on the shaft, everything should be measured relative to the shaft, if you can.

Thanks. Brad.
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Old 01-04-2024, 09:29 PM
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Gary,

Changing the angle isn’t really what you’re after. It’s blade area in the right place. Think of rake as an extension of the working face of the prop blade, in the area the water will be headed to as it is forced rearward and slung outward.

Without welding material back on, you will only be able to reduce effective rake. If you remove material from the trailing edge toward the tips, that will reduce rake. But if you remove material from the trailing edge toward the hub, it won’t really increase the rake, as it won’t extend the distance the water will stay engaged with the working face of the blade. It will make the prop easier to turn, though, but at the sacrifice of lift (if memory serves correctly).

Thanks. Brad.
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Old 01-05-2024, 07:15 PM
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Thx Brad.

You did a great job of explaining it and is what I was thinking but couldn’t explain.

Which is different than orig posts.

At least my understanding of them.

If they’re determining rake by putting a protractor on the trailing edge of A blade, that means if I manipulate that edge, I change rake.

Which I did not agree with.

Originally Posted by Brad Christy
Gary,

Changing the angle isn’t really what you’re after. It’s blade area in the right place. Think of rake as an extension of the working face of the prop blade, in the area the water will be headed to as it is forced rearward and slung outward.

Without welding material back on, you will only be able to reduce effective rake. If you remove material from the trailing edge toward the tips, that will reduce rake. But if you remove material from the trailing edge toward the hub, it won’t really increase the rake, as it won’t extend the distance the water will stay engaged with the working face of the blade. It will make the prop easier to turn, though, but at the sacrifice of lift (if memory serves correctly).

Thanks. Brad.
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Old 01-05-2024, 08:37 PM
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Rake is easy to see.

15* rake :



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Old 01-05-2024, 08:39 PM
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18* Rake
You can see the "bend" where the blade is further from the shaft



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Old 01-05-2024, 08:45 PM
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On my heavy straight bottom 15* rake is slower than 18* rake ...it grabs harder at idle during a shift, rpm drop is significantly more than an 18*

18* carries the bow better I`m told and that makes sense , less boat out of the water .(3mph faster) Doesnt drop rpm at shifts, that part is really nice .

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