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Thread: No speed at full throttle / high RPMs

  1. #1
    Join Date
    Sep 2019
    Location
    AZ
    Posts
    2

    Default No speed at full throttle / high RPMs

    I?ve got an American Express a.k.a. Henglong 3837 Atlantic boat that I?m trying to upgrade with new drive shafts and propellers. When I start out slow the boat moves ok but when I get past 1/2 throttle there is no pick up and it looks like the propellers are creating splash but not pushing water. It has a twin motor setup spinning in counter rotation with 3 blade 36mm propellers. These are the propellers I installed:

    uxcell RC Boat Propeller 4mm... https://www.amazon.com/dp/B06XJ3SWSH...p_mob_ap_share

    Not sure what?s wrong. Is this what cavitation is? It originally came with 2 blade propellers that worked fine but one broke. Should I just go back to 2 blade propellers?

    I know these boats can go much faster there are YouTube videos of it on the internet:

    https://m.youtube.com/watch?v=Jesq0AfZdoA
    https://m.youtube.com/watch?v=vn22QfI3bjc

    Totally new to RC boating so any help is appreciated. TIA!

  2. #2
    Join Date
    Apr 2007
    Location
    AZ
    Posts
    7,686

    Default

    Not all propellers are created equal, even with the same diameter, pitch and number of blades. The most likely explanation is poor propeller design which is causing severe cavitation. First, install the original propellers and see if that works. Next try a set of decent quality props like the CNC variety OSE offers.

    I am nor familiar with that boat or the specs on the original props, but you should be able to upgrade performance with the right props, 2- or 3-bladed. The risk is that as you increase prop diameter, pitch or blade number you will stress the motor, ESC and packs. So, you can go too far and break something.

    I know this is pretty general but I won’t recommend props unless I know more about the boat. Have you looked at YouTube videos for modifying this boat?
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  3. #3
    Join Date
    Apr 2007
    Location
    ON
    Posts
    2,307

    Default

    You said that some videos show the boat going a lot faster then yours.
    The differance between the two videos that you listes is the boat in the upper video has been modified with brushless motors and ESC;s to match.

    Here are the replacment props.

    http://www.heli-parts.com/3837007-pr...l-p-14507.html

    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

  4. #4
    Join Date
    Sep 2019
    Location
    AZ
    Posts
    2

    Default

    Thanks for the replies. One of the original props broke which put me down a big rabbit hole. I thought instead of getting replacement ?toy? props, I would do a few upgrades as seen on YouTube. I ended up ripping out the original drive shafts and replacing them. The original props don?t fit the new 4mm shafts.

    I can try different props but wasn?t sure what direction to go in. 2-blade vs 3, pitch, size, etc. So the problem I?m describing does sound like cavitation? Ill try to take a video of it and post it here.

    Thanks!

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