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Thread: Center of Gravity

  1. #1
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    Default Center of Gravity

    Hello,

    I've come to realize that CG is pretty important on these boats, and I'm wondering where the ideal CG for a 27" mono is approximately? Should it be more towards the back or front?

    Thanks in advance

  2. #2
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    Cool

    It depends on the hull design and the speed, but try to keep it between 7.5" and 8.5" forward of the transom. This will get you close.



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  3. #3
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    Default

    sorry but what's the transom? I'm a bit new to boating.... thank you!

  4. #4
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    Default

    i'm pretty sure the transom is the back of the boat...
    if it ain't broke you ain't trying hard enough.
    if at first you don't sucsed maby failure is you thing.

  5. #5
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    Cool

    Sorry - yes the transom is the flat surface at the back end of the boat onto which the rudder and trim tabs are attached.


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  6. #6
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    Default

    ok well instead of making a new thread to ask the same question i'll just ask it here...where abouts it the ideal CG on a 27 inch cat?
    if it ain't broke you ain't trying hard enough.
    if at first you don't sucsed maby failure is you thing.

  7. #7
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    Default

    Quote Originally Posted by LST XXL View Post
    ok well instead of making a new thread to ask the same question i'll just ask it here...where abouts it the ideal CG on a 27 inch cat?

    I say between 8 1/2 and 9" approx 33%
    SPRINT CAT 40.........BOOGIMAN 25" MONO 8xl
    EX President of the Offshore FE Vultures Society

  8. #8
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    Default

    Sounds good thanks Fluid

  9. #9
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    Default

    Me too!!

    What would be the CG for a 25 mono? here: http://cgi.ebay.com/ws/eBayISAPI.dll...m=300268910685

  10. #10
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    Default

    Quote Originally Posted by M.M. View Post
    Me too!!

    What would be the CG for a 25 mono?
    It is approx 30 % forward of the transom as a starting point.
    For a 25" that will be 7.5"
    See it....find the photos.....sketch it it....build it........with wood

  11. #11
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    Default

    So do i place a battery on each side approx. 7" inches to the back or center of the battery?

  12. #12
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    Default

    i think it would be to the center of the batery
    if it ain't broke you ain't trying hard enough.
    if at first you don't sucsed maby failure is you thing.

  13. #13
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    Quote Originally Posted by M.M. View Post
    So do i place a battery on each side approx. 7" inches to the back or center of the battery?
    Battery position will be dependant on where the boats balances.
    Batteries are usually the best way to adjust and set Cg.
    Have the boat ready to run as such so that includes Rx pack etc.
    Place the batteries where they can be moved back and forth and see where the boat balances.
    Use the packs to get the Cg point that you want and mark their position. Sort out your securing method, commonly velcro straps, and fit.

    My new 30" mono has a 4S pack in front of the motor on its own "bed" and has the ability to move my Cg from 27-33% If I need a Cg outside hese parameters i will have to use ballast.
    See it....find the photos.....sketch it it....build it........with wood

  14. #14
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    Default

    Bath tub testing time!!!!
    LMT
    LehnerMotorenTechnik.com

  15. #15
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    Default

    Bath tubs are great for lateral stability checks. left to right balance, and to check a hulls self righting ability if any. Leaks show up real fast in the bath too.
    A float test will not normally get you your Cg setting.

    For a good estimate you mark the edges of the hull and place your fingers under this point(s) This gives you a very good idea of the fore/aft (forward / rearwards) balance point.
    I'll not go into the long side of it but a true centre of gravity is very different to a centre of balance that we usually refer to in model boat hulls.
    Cg, CoB, CofG are all very common terms to describe the same thing that we are often after.
    Fingers or better yet is pencils under the nominated balance point and then move the batteries to get the balance.
    I do a Cg check of my riggers before ALL runs to ensure that it is good to go.

    If I have confussed anyone please sing out and I'll grab the camera and do a pictorial version of this description.

    I am always keen to help.....and learn more.
    See it....find the photos.....sketch it it....build it........with wood

  16. #16
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    Default

    I think I get what you are saying but a pic is worth a thousand words. Pic's please

  17. #17
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    I have a 53" cat. 1/3 would be 17" however it balances at 21" it that OK. Boat is a Aquacat Segad

  18. #18
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    Default

    This thread is 11 years old, the OP hasn’t been back to the forum in 9 years. It would be best to start your own thread rather than reviving a zombie thread where participants are long gone from the forum.



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