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Thread: Recomended RPM range explained

  1. #1

    Default Recomended RPM range explained

    so we all have read it here at OSE a few times if you ever bought a motor.

    OSE Suggests 20,000-35,000 total rpm for boats. We suggest most Fast Electric Boaters should run in the 25,000RPM range for Sport Boating or 30,000RPM Range for racing. These are only guidelines, we suggest if you do not have the knowledge to pick the correct motor, please consult us first or other members of the rc fast electric boating community. Either at a local club or on our OSE Forums.

    My question is what is the science in the eqaution?
    A uniformed consumer may assume higher rpm means faster top speed.
    What's the danger of going beyond these recommended rpm ranges?

  2. #2

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    Higher rpm usually means the potential for very high amp draw especially if even a slightly too large of a prop is fitted for “higher speeds”. Racers are more likely to be aware of high amps, plus they usually don't run for more that two minutes, reducing the risk of excess temperatures. Sport boaters are more focused on long run times which means higher temps and a higher risk of damage. It is the high temperatures which damage ESCs and motors, not amps. This is why racers often get away with setups which cause a burn down in a sport boat. Sport boaters who copy winning race setups are often victims of severe damage.

    An aware boater can exceed the rpm/amp draw limits with safety, but many years of experience has shown that the average sport boater runs a large risk of burning down. This is the reason for a more conservative approach to motor selection recommendations. If a new boater burns down on his first attempt, he/she is less likely to remain in the hobby.


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  3. #3

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    There's no real danger if you follow some rules. The best thing to do is see what others with the same boat are running in the speed range that you're looking for. Then you can copy it, or go for a faster setup. Temp everything on a hot setup every 30 seconds. If anything is stressing, it'll get hot. There are people that think 6s on a 2200Kv motor is a recipe for fire...no, it's not. Do a lot of reading on the subject...you'll figure things out quickly.

  4. #4

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    Quote Originally Posted by Prodrvr View Post
    There are people that think 6s on a 2200Kv motor is a recipe for fire...no, it's not.
    Yes it is. Especially if you don't have the experience Jay mentioned.
    glue sniffer

  5. #5

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    Here is a Tenshock Electra twin setup 2 x 2200kV and 2 x 6S


    https://www.youtube.com/watch?v=RxnB2u26-qc


  6. #6

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    Quote Originally Posted by T.S.Davis View Post
    Yes it is. Especially if you don't have the experience Jay mentioned.
    Typical racer answer lol...j/k. You don't need that much experience, just a brain that works.

  7. #7

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    Quote Originally Posted by Alfa Spirit View Post
    Here is a Tenshock Electra twin setup 2 x 2200kV and 2 x 6S


    https://www.youtube.com/watch?v=RxnB2u26-qc

    That's cool!

  8. #8

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    I'll try to keep this simple and civil () This "controversy" can (like the Elephant that's always been in this room) be seen from two different sides :

    A] : The actual racer who needs a boat rigged to do a mill + six + one extra laps on the 1/6 mile oval, come in and survive to repeat 3 or four times an afternoon and

    B] the sport boater who sees pretty much only the need to go max-banzai for two to three seconds to get his ya-ya's.

    The "Type A" situation will mostly stick to the tried and true lower KV guidelines for obvious reasons - reliability and predictable handling on the course

    "Type B" rigs can overpower/overvolt for that momentary thrill of the (psuedo) saw pass if that's what satisfies their aspirations

    Whatever gets yer toes to tappin and your wallet to pop open
    2008 NAMBA P-Mono & P-Offshore Nat'l 2-Lap Record Holder; '15 P-Cat, P-Ltd Cat 2-Lap
    2009/2010 NAMBA P-Sport Hydro Nat'l 2-Lap Record Holder, '13 SCSTA P-Ltd Cat High Points
    '11 NAMBA [P-Ltd] : Mono, Offshore, OPC, Sport Hydro; '06 LSO, '12,'13,'14 P Ltd Cat /Mono

  9. #9

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    Yeah, I'm Type B for sure. Overpowered for saw passes...nothing better.

  10. #10

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    Quote Originally Posted by Alfa Spirit View Post
    Here is a Tenshock Electra twin setup 2 x 2200kV and 2 x 6S


    https://www.youtube.com/watch?v=RxnB2u26-qc

    To be fair these guys are unlikely to got too hot running in ice cold water.
    NZMPBA 2013, 2016 Open Electric Champion. NZMPBA 2016 P Offshore Champion.
    2016 SUHA Q Sport Hydro Hi Points Champion.
    BOPMPBC Open Mono, Open Electric Champion.

  11. #11

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    Great discussion guys.
    Thanks for the great responses.

  12. #12

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    Quote Originally Posted by Peter A View Post
    To be fair these guys are unlikely to got too hot running in ice cold water.



    Plus they stay WFO less than 3 seconds at a shot. They are very nicely trimmed, run sweet, and I'd bet their pilots were having a ball

    That's What it's All About (except for the Hokey Pokey)
    Last edited by properchopper; 09-12-2018 at 05:24 PM.
    2008 NAMBA P-Mono & P-Offshore Nat'l 2-Lap Record Holder; '15 P-Cat, P-Ltd Cat 2-Lap
    2009/2010 NAMBA P-Sport Hydro Nat'l 2-Lap Record Holder, '13 SCSTA P-Ltd Cat High Points
    '11 NAMBA [P-Ltd] : Mono, Offshore, OPC, Sport Hydro; '06 LSO, '12,'13,'14 P Ltd Cat /Mono

  13. #13

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    Quote Originally Posted by Prodrvr View Post
    Typical racer answer lol...j/k. You don't need that much experience, just a brain that works.
    I was gonna go with "typical world record holder" but my record was beaten.
    glue sniffer

  14. #14

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    Ok ok, but I like fast boats lol

  15. #15

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    If you are doing saw passes you may get away with the 2200kv on 6s.

    If you try that 2200kv in the oval racing on 6s for 6 laps you will learn quickly why you need to avoid those high rpm setups.

    I think offshore recommendation is spot on. 25000rpm for sport boating and 30000rpm range for racing.

    This recommendation should keep the amps with in a safe limit for the longer runtime of sport boating. And for the length of an oval race.

  16. #16

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    I'm new to all this FE brushless stuff but I am learning from you guys about it and about proper boat set up also. You need to properly set up your drive angles as well, I think I burnt up the original HK 120 in my Genesis dues to the hull running too wet (bow down too much, not sure if that is negative or positive and the drive angle). I changed my drive angle as suggested on here and never burnt up another ESC but I did switch to a 180 after burning up the 120. I don't know much except for it seems like there is a lot of variables in getting a good reliable running boat. Not just how big your batteries are and what KV your motor is. I have been following advice I got on here and I have a great "sport" running Zonda, I love it! It is fast and reliable for the sport running I do.

  17. #17

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    One thing I forget to mention even with those rpm guildline becareful not to over prop.

    For the sport boater I think a 42mm prop example x442, x642 or smaller with the 25000 total rpm is a safe guild line setup.

  18. #18

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    Crash, what are your speed goals?

  19. #19

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    Look at this Twin setup Genesis, 2 x Scorpion 3026 - 1400kV and 7S

    36000 RPM unload.

    https://www.youtube.com/watch?v=o3KCKjPuZkc

  20. #20

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    Quote Originally Posted by Alfa Spirit View Post
    Here is a Tenshock Electra twin setup 2 x 2200kV and 2 x 6S
    Adding a second motor reduces the load each one sees..

  21. #21

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    Quote Originally Posted by Prodrvr View Post
    Crash, what are your speed goals?
    70 mph was my goal , I hit 68mph recently before a blow over.
    I ordered a 94 mph prop to play with someday, I dont have it yet. Octura 2352
    its just for a speed pass, i dont have any idea how many amps a 4.7pitch prop will draw......lol

    my set up is two 5s lipos parallel with 1750 kv and a 52mm prop
    Last edited by Crash; 09-13-2018 at 07:22 AM.

  22. #22

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    2 x 5s lipos and 1750 kv motors ok but what is your hull ?

  23. #23

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    36 inch mono
    its heavy loaded up with lipo rtr it is 172 oz.

  24. #24

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    Crash.
    Here's a chart that shows good numbers for oval & sport running if you stay in the red band.
    For the 'point & squirt' type of running you can go a bit higher in the kv.
    Motor KV_Batt.jpg

  25. #25

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    Quote Originally Posted by 785boats View Post
    Crash.
    Here's a chart that shows good numbers for oval & sport running if you stay in the red band.
    For the 'point & squirt' type of running you can go a bit higher in the kv.
    Motor KV_Batt.jpg
    thanks for that.
    I wonder if this set up would like 6s better due to the weight of this boat, I am running a 52mm prop to get this boat to move like I want it to. at that size prop I am drawing 275 amps on flat water 100% throttle at times.

    more volts may bring the amps down …..?

  26. #26

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    The problem I have with all these high rpm recommendations is that this forum gets a ton of lurkers. Nothing wrong with that really. Read read read. You can learn a ton just with the search tool. So new guy comes here reads basically "if you want to go fast, go with gOzillion rpm. Screw the racers they don't know anything" All he hears is "fast". "I wanna go fast fast fast".

    So he builds a 2000kv 6s boat with no idea what's what. Gets the gap on the drive dog wrong. Maybe has an imbalanced prop. Struts the wrong depth. Or maybe he gets the CG wrong so it runs super wet. Even if he gets it all right he may run it for 8 minutes. Burns the whole thing to a crisp and we never hear from him again. He's out of the hobby.
    glue sniffer

  27. #27

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    Totally agree Terry.
    Burnt a 4082 2000kv motor myself in a 33" mono. A well trimmed 4s race boat that I decided to try on 6s with a smaller prop. It lasted only 3 laps.
    Mind you, it was only a Leopard motor though.

    I'm trending to run lower kv motors lately.
    My twin cat runs HET Typhoon 650-68-1600kv motors. Originaly built as a 6s class boat with 4214/3 blade props.
    But I also run it in our 4s class with 4718/3 blade props.
    It beats the cats running much higher 2200 plus kv motors.
    Under our rules both motors must run off the same single 4s pack. I still have 30-40 percent left in a single 6000mah pack after a race.
    Fast & efficient.

  28. #28

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    33 1/2" mono, 6s, 2000Kv...runs full throttle for the entire pack, nothing comes back hotter than 130. AQ Motley Crew...6s 2075Kv...would run 4 full throttle passes...nothing came back hot. I agree that a new boater burning stuff up from the get go will make them give up. However, if they educate themselves first and move up gradually, they'll have a boat that does what they want.

  29. #29

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    Quote Originally Posted by Crash View Post
    I ordered a 94 mph prop to play with someday, I dont have it yet
    A whaaaat?

  30. #30

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    Quote Originally Posted by Prodrvr View Post
    A whaaaat?
    John

    It looks like he has ordered a Octura 2352
    52mm - Dia
    2.3 pitch ratio = 120mm of pitch

    a Octura 452 is only 62mm of pitch

    He is now drawing 275Amp with a 452
    2350 Prop - he would need 140 C batteries and a 500Amp ESC. and watch out for the

    Larry
    Past NAMBA- P Mono -1 Mile Race Record holder
    Past NAMBA- P Sport -1 Mile Race Record holder
    Bump & Grind Racing Props -We Like Em Smooth & Wet

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