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Boat Prop Theory

Old 09-30-2004, 11:15 AM
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RussF
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Default Boat Prop Theory

I would like to learn about boat props. Are there any good resources to read that someone could point me towards. I would like to learn what effects shape, size, and pitch have on props for boats in relation to motor size and speed. Sorry for such a newbie question but I'm always looking to learn.
Old 10-01-2004, 06:07 PM
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cimmy
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Default RE: Boat Prop Theory

Hey Bash Check out http://www.offshoreelectrics.com he has a few articles and I think a chart but not sure.
mike
Old 10-04-2004, 11:16 PM
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Default RE: Boat Prop Theory

I'm looking for the same thing, just spent an hour on offshore's site. very good info.
What exactly is pitch and how is it measured?
Old 10-05-2004, 06:03 AM
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Raydee
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Default RE: Boat Prop Theory

Try this one too

http://www.rcprops.com/rcboats/cats/index.html
Old 10-05-2004, 11:49 AM
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Default RE: Boat Prop Theory

thanks, nice site. I think I need the basics like what is pitch ?

I figured out that larger diameter and larger pitch is like gearing up I think.........just don't know what pitch is yet. Could it be the height or the amount of curve on the prop?
Old 10-05-2004, 01:06 PM
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Default RE: Boat Prop Theory

Pitch is the distance the prop makes the boat go forward, in one rotation (if there was no slip from the water).

A prop with a high pitch will propell a boat faster than a low pitch prop, with the same RPM.

It's nice work to play with pitch and size to see what works best for the boat and motor.

Regards, Jan.
Old 10-05-2004, 01:23 PM
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Default RE: Boat Prop Theory

That's what I'll do, it seems the hammer is kinda oddball size at 3mm.
Old 10-06-2004, 11:14 AM
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Default RE: Boat Prop Theory

Yes it is a bit weird of a shaft size at 3mm but I think the 1/8 props should fit ok. Anyway the stock prop is 55mm of pitch. Which I understand means that for one rotation it will travel 55mm (2.16535 inches) with no slip. And its 32mm (1.25984) of diameter. So if a prop smaller in either pitch or diameter it will spin faster than a larger prop. And if it spins faster the boat should go faster. But if there is too much pitch or diameter and the prop is pushing too much water then the motor will never reach its best RPM. So it seems to me that you would need to experiment with different diameters and ptich to see what prop allows your specific motor to operate its best RPM and efficiency. This would be indicated by speed, runtime on the batteries, and heat buildup in the motor and electronics. A good balance of all things should be the goal ..... Right? Am I on the right track or do I still not undersand? Assuming I am correct then I still have a question. Does the diameter of the prop or the pitch have the greatest effect on speed gains? In other words I am thinking that by using my stock prop at 32x55 and cutting it down it might spin faster. If is spins faster I would have less torque and more RPM thus a faster top speed. The Hammer EP has alot of torque in my opinion because it just about jumps out of the water. So I would like to trade some of this torque for top speed hopefully. Is that possible? Or would I be better to try a prop with a larger diameter but less pitch? Like a 35mmx35-40mm or something?
Thanks for you discussion people, just when I think I understand something I get confused again. [sm=bananahead.gif]
Old 10-06-2004, 03:36 PM
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pompebled
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Default RE: Boat Prop Theory

This is where experimenting is in order.

On my 12 cell mono I usually run a Graupner 45K Hydroprop.
As I have a runtime of over 7 minutes, and the race-heats are only 6 minutes, I tried to get more speed at the expence of the runtime.
Putting on the nexts size prop was no succes; the motor did not rev high enough anymore, the batteries were cooking and the increase in speed was negligable.
As the Graupner props all have different pitch, the combination of a bigger prop with higher pitch was too much for the motor and batteries.
I cut down the 48K down to 45mm and now have the advantage of the higher pitch (= more speed) while the motor revs high enough to keep everything cool.
The increased torque makes the boat a handfull when there is more than a little chop, barrelrolls at full speed are no problem.
As this does not help on a race day, I only run this prop in smooth conditions, in choppy water I run the 45mm prop and settle for less speed and better boathandling.

Regards, Jan.

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