Why a smaller prop for higher "s" battery?

[wht73]

Hey guy’s, I’m a newb here to the rc boating thing (my sons and I have many rc buggies,sc trucks,truggies)
and It’s WAY more fun than I thought it would be.

I’m just stumped on the whole prop thing. I guess it’s like pinion gears on land but..

Why a smaller prop for higher "s" battery?

I noticed in surfing this site and reading a lot of posts, that the trend to use a smaller in diameter prop
ie ; 36mm vs 40mm for 4s vs 3s batteries are needed.

Could someone please explain this for me.

I know this is a “general” theory, and it is a combo by combo thing

I just need it to get it into my thick head.

Thanks in advance

Chris

[wht73]

My 1st post on this site and already it's in the wrong section!

What a newb!!

I told ya I had a thick head.

Could someone please move this to prop talk.

Thanks

[detox]

When you start burning things up you will understand that smaller props will pull less amps. Also some boats handle better using smaller size props.

[de-pro]

Its all about the amp draw and the ratings of your electronics and the battery.
lower kv motor with more voltage runs much cooler and produces more torque so you can use a bigger prop.
As the kv goes up, your voltage has to come down. Also the size of the boat will determine the setup as well.
These are just the basics and there is lot more factors involved like the C rating of your battery, 2p versus 1p, etc....

[electric]

The whole thing will drive you crazy, and then at some point the light will come on.
1. The bigger the prop the faster you go(to a point), BUT then your amps go up(more load on the motor) and that generates heat which will burn up your motor and or esc.
2. The Voltage 14.8 volts (4s) times the KV of your motor will give you how many RPM's your prop is turning. Too many rpms, and the driveline comes apart and the prop because less effecient. To few will not work for you either. There is a sweet spot for this and I had a chart somewhere, but haven't looked at it in a long time.
3. 150 degrees is a pretty good ball park number for your motor, esc, and batteries (MAX). I like to run around 130's max, but it is somewhere in that range.
4. There is not single answer for any setup, it is a balance of hull, setup of the boat, voltage, motor, prop, driveline. That is why you will not get straightforward answers to a lot of things, but good guidelines.

To your question. The higher voltage (s thing) means that you will be turning higher rpm's on your motor. If you keep the same prop on, it will pull more amps and thus be more likely to fry your motor or esc. You can offset this by putting less load on the motor by putting a smaller prop on. It's a balancing act.

[wht73]

Thanks for the replies. I get the whole leverage thing. Makes sense.

I have a EKOS with 2 2860/3400kv mtrs that replaced 2 arc 2848/2800kv mtrs w/ 120a esc's and 40mm cf counter props.

53mph

They ran nice and cool (before being submerged). around mid to high 80's with the ir gun after a long run.

The only reason I replaced the arcs is a cooling hose got bit up by the coupler and drowned the mtrs.

One survived, one did not. I plan on buying 11.2 batts to get the cg balanced and batts down in the sponsons
but for now I take it easy with the 14.8's and the 36mm props.

[Steven Vaccaro]

Just because someone says to go to a smaller prop, doesn't mean thats the prop you have to stick with. Most times its a suggestion for a starting point. If you start small and work up you will have a happy system. If you start large and burn it up, you will have an expensive/smelly paper weight.

[wht73]

Good point Steve!

[BHChieftain]

The whole thing will drive you crazy, and then at some point the light will come on.
1. The bigger the prop the faster you go(to a point), BUT then your amps go up(more load on the motor) and that generates heat which will burn up your motor and or esc.
2. The Voltage 14.8 volts (4s) times the KV of your motor will give you how many RPM's your prop is turning. Too many rpms, and the driveline comes apart and the prop because less effecient. To few will not work for you either. There is a sweet spot for this and I had a chart somewhere, but haven't looked at it in a long time.
3. 150 degrees is a pretty good ball park number for your motor, esc, and batteries (MAX). I like to run around 130's max, but it is somewhere in that range.
4. There is not single answer for any setup, it is a balance of hull, setup of the boat, voltage, motor, prop, driveline. That is why you will not get straightforward answers to a lot of things, but good guidelines.

To your question. The higher voltage (s thing) means that you will be turning higher rpm's on your motor. If you keep the same prop on, it will pull more amps and thus be more likely to fry your motor or esc. You can offset this by putting less load on the motor by putting a smaller prop on. It's a balancing act.

Here's the chart--I forgot who orginally posted it...
Chief

[JIM MARCUM]

With Stephen (as usual). The above chart is a good place to start. Keep the motor temp below 150 & prop up slowly. Plenty of good info here on trimming your boat - prop strut height/angle & Center of Gravity, etc. right here on OSE. Welcome to the FE club. JIM

[wht73]

Thanks for the welcome.

I'm probably going to end up using 3's to get the CG a little better by geting them in the sponsons.

4Kah 4.'s would probably fit as they are thinner than my 5k ones.

[JIM MARCUM]

Which hull are you running? JIM

[wht73]

EKOS Cat w/twin mtrs.

[Steven Vaccaro]

With Stephen JIM

Its Steven with a "V".

[wht73]

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