KV versus prop size.

[Simmo]

Hey guys, seeking opinions with pros and cons on the following scenario comparisons. Information obtained from Radio Control Info, RCI FE Boat Calculator.

Say 800mm mono, 4072 1400KV on 6S running a 450 prop.
Amp draw - 114.4A.
Battery load capacity - 35%.
Loaded RPM 25,538.
Speed - 54.8 MPH.
Motor temp - 64C.
Overall efficiency - 80%.

Say 800mm mono, 4072 2000KV on 6S running a 440 prop.
Amp draw - 111.7A.
Battery load capacity - 34%.
Loaded RPM 38,557.
Speed - 56.1 MPH.
Motor temp - 52C.
Overall efficiency - 84.8%.

Stating the obvious that the RPM is far higher on the 2000KV scenario thus creating more wear but the temps are lower, the overall efficiency is greater and the speed is greater.
You could also use a 438 prop and have the following result, far less amp draw, less battery load capacity, greater overall efficiency with the only downside a slight drop in speed.

Say 800mm mono, 4072 2000KV on 6S running a 438 prop.
Amp draw - 87.6A.
Battery load capacity - 27%.
Loaded RPM 39,723.
Speed - 52.5 MPH.
Motor temp - 45C.
Overall efficiency - 86.2%.

Comments?

[Panchothedog]

I don't know where the information you got came from even though you posted it,and I am sure I can't prove or disprove any of the calculations but my practical experience tells me that an 800mm mono hull ( 32 inches ) with a 38 mm prop is not going to run in the 50+ mph range. Set up with a surface drive as most FE boats are it would probably be lucky of it could get up on plane. Just my opinion,but that is what you asked for.

[Simmo]

Here is the website. www.radiocontrolinfo.com/rci-fe-boat-calc

Just interested in peoples point of view, that's all.

I currently have a TFL Pursuit, SSS 4092 1650KV on 6S running a 447 prop, GPS'd at 54 MPH. Also, a TFL Hobby Party (820mm long), TP3650 1950 KV running a 442 prop, GPS'd at 59 MPH. Absolutely no issue getting them to plane and very close to the above website information. Just feed the info into the drop boxes and press submit.
I am not looking for solid answers, just peoples experiences and what works best for them.

[martin]

The smaller you go with prop size even allowing for higher kv & higher rpm the smaller prop will be less efficient at pushing the boat than larger diameter/pitch props. Example is if you put say a 450 prop on a 41" mono which would suit that size hull, then put a 438 prop on even allowing for higher kv & rpm. The 438 prop would be very inefficient at pushing a 41" with lots of prop slip, producing slower speeds in the real world.

[Panchothedog]

Holo Simmo. I also have a pursuit ( great boat ) with a leopard 40x82
1600kv that I run on 4,5,or 6s depending on what's next in my battery box and I use mostly 45 or 47 mm props. When I really feel like pushing it, which is not often I have a x448 that I have put on it and hit 61 mph on smooth water trimmed really loose. A very forgiving fun hull.

[Simmo]

Thanks for the response Panchothedog. Totally agree, great stable hull and hard to flip. Like your setup, around 1600KV with those size props you mentioned works really well. Relatively low amp draw and low temps. I have swapped the motor out on mine as a trial for a Leopard 4082 2000KV on 6S with a 440 prop and get similar results to the 1650KV set up. Just starting to build a Delta Force DF 33 that will have a Leopard 4082 2000KV on 6S, I'm interested to see the comparison with the Pursuit once built.