Prop Dimpling

[Boaterguy]

I had an Idea the other day, this is just a theory, it is not tested, I thought it might be neat to try though. Here goes: If dimpling a golf ball makes the air stick to it longer, wouldn't dimpling the backside of a prop help suck more water over the next blade? it might even give enough suction to pull the boat forward more. Any thoughts? I know some racers leave the backs of the props rough, is that generally the same idea?

[Fluid]

Water and air are not the same. A round ball spinning through the air is not a propeller spinning in both water and air. Google golf ball dimples and you'll understand better.



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[7500RPM]

Just do not polish the working face of the prop, I use a low pressure sandblaster to rough up the face a little..

[m4a1usr]

Water and air are not the same.

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Exactly. Air is compressable. Water is not. At least with the force we have available for our use.

John

[Boaterguy]

I'm not talking about compression, but I understand what you mean, I just thought it might work.
7500: Why is the working surface rough?

[7500RPM]

Do a search on google, and see some of the stories and tests, and what some of the pro boat racers do

there are pictures on the net of some of these props and the finishes on them.

http://www.screamandfly.com/showthre...olish-vs-satin,

http://www.fastelectrics.net/propeller_preparation.php

[royboy]

I worked for a coating company uct coating here in florida and we had rolls royce due testing and there was defanitly a performance gain. The coating was like tiny microscopic balls all stacked together which cause very small cavatation on the prop to reduce drag. So having a slightly ruff bladed prop would due the same.


Roy

[Fluid]

Since the front facing surface of the prop blade runs almost completely in air, the surface finish there is not as important and a case could be made that polished is better. The above links notwithstanding, there is a big dispute in boat racing circles about the "best" finish for racing props, everyone thinks they have the answer. I have never seen a dimpled surface like a golf ball because the reason for the dimples' success does not apply at all in boats. FWIW, the fastest FE boat in the world did not use a highly polished prop.


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[Boaterguy]

I was more referring to the back face, the water would be drawn over the back of the propeller blade and that water moving backwards might help "pull" the boat forward, kinda like a satin back face.

[egneg]

This debate has resurfaced several times. The shape has a great deal more to do with performance than the finish on the prop. Unless someone has access to scientific controlled studies - it's only someone's opinion.

[Fluid]

This debate is constant among boaters, not just resurfacing now and again. One of the fastest R/C boaters, Andy Brown, says this: "Matt finish is faster and with some prop/boat combo's the difference can be significant." http://www.intlwaters.com/index.php?showtopic=11023 Yet I have seen some very fast boats with shiny props. IMO there is no definitive answer.

Water moving backwards "pulls" the boat? No it is simpler than that - or more complex depending on how your mind works. http://rcboat.com/527_3.pdf


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[Boaterguy]

It's hard to explain, basically just a satin finish on the back.

[jonjon00]

This debate has resurfaced several times. The shape has a great deal more to do with performance than the finish on the prop. Unless someone has access to scientific controlled studies - it's only someone's opinion.

I love this debate. I tend to agree with egneg, finish on the blades has little affect. So little that unless the whole rest of your setup has been proven flawless you should not be concerned with it. But, I do llove the look af a nice shiny prop hanging off the back. The general ideas lean towards a polished face being beter for S.A.W. speed runs since prop face hangs on to the water and gets maximum loading. Satin/rough face works better for oval since the micro cavitation that happens on the blades prevents maximum prop loading creating better performance through the turns. The theory is sound, but I don't have time to prove it while I still have a job.