electric golf cart inboard design, need help!

Discussion in 'Propulsion' started by Archangl7, Sep 4, 2018.

  1. Archangl7
    Joined: Aug 2017
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    Location: clearwater, fl

    Archangl7 Junior Member

    So, at the moment i have several solar panels, 2 charge controllers and a bunch of batteries. I also have an electric golf cart motor rated at 4hp with the controller. the reason i want to use these motors is price and how easy they are to get here in Florida. The question is two fold. First, what is the best way to get the drive shaft outside the hull? A straight stern drive like a sailboat seems best, but from my understanding it will always let water in for lubrication, so that is a cause for concern with electronics inside. Second, how would i calculate a prop for the desired application. It will be a cat style boat 16' and each sponson is 2.5 ft wide. displacement will be about 1ton at 1.5ft depth. i have nice cutting hull shape, and a transom that lifts up as it goes back, so drag shouldnt be much of an issue. I just am toying with how i want it driven. Sorry, the pic doesnt show the up curve on the transom, but you get the idea.
     

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  2. JamesG123
    Joined: Mar 2015
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    Location: Columbus, GA

    JamesG123 Senior Member

    The attached pic is of one of the hulls? You want one motor & prop at the stern of each hull? Or you want one motor and screw total, I guess in the center?

    Prop selection depends on the power curve at given rpms and where in the case of an electric, what rpm gives you the most thrust for the power you have. I'm sure a guru will post soon.
     
  3. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    You designed a hull that seems better fitted for high power and high speeds. The buttock lines are straight and the deadrise is pretty constant for most of the run. That is more typical of a planing hull. Look at sailing cats (cruising not racing) and they will give you an idea of lower speed shapes.
     
  4. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    As mentioned above, the hull is quite unsuitable, drag certainly will be an issue, and presumably you will have a drive in each side ?
     
  5. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    When you get the hulls sorted, you may like to think about using a prop on the end of a long shaft, a bit like those Long Tail boats in Asia.

    With such low horsepower, and limited charge, your setup reminds me of those high performance human powered boats.

    In that case, they simply used 3/8" stainless shaft with a large model plane prop on the end of it.

    The secret is that the long tail prop doesn't need to have much support, as the propeller "self centres" under power, and doesn't flop about from side to side under when running.

    You can easily mount the motor above the water, and immerse the prop on the end of the shaft. The other advantage is that it's easily retractable for rocks, weeds, beaching etc.
     
  6. Archangl7
    Joined: Aug 2017
    Posts: 9
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    Location: clearwater, fl

    Archangl7 Junior Member

    i used an older screenshot, i did modify the back end already. yes, i mean to have a drive in each sponson for 2 per boat. I had considered using one of the the shafts advertised as a drill attachment that went into a sort of coupler to the motor. I am sure a drill cant produce a force that that motor can, but if it holds up it might work given most drills dont much above 400 rpm, and the motor will do 4,000.
     

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  7. Archangl7
    Joined: Aug 2017
    Posts: 9
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    Location: clearwater, fl

    Archangl7 Junior Member

    i had given thought to the idea of buying just the drive shaft portion of a mud motor, and using an electric instead of gas for the power. I can get one of those that handles up to 18hp for about $500.
     

  8. Archangl7
    Joined: Aug 2017
    Posts: 9
    Likes: 0, Points: 1
    Location: clearwater, fl

    Archangl7 Junior Member

    I did look at some other cat hull designs but they are all too thin to hold any substantial amount of weight. Being that this will be a slow mover, i thought drag might not be such a great concern, and i wanted it to be able to carry many people as a ferry type of vessel. I could basically mirror the bow to the stern, but then my center of gravity would be way forward, and the deck would be more centered and i dont like the idea/look of that.
     
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