8 ft. boat needs propulsion solution

Discussion in 'Boat Design' started by Sandy1, Oct 5, 2015.

  1. Sandy1
    Joined: Mar 2015
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    Sandy1 Junior Member

    Hello everyone. I have an eight foot skimmer wood boat that I am building. The boat needs to be electric for the waterways I would like to access. I know I know. Everybody hate electric. Well most everybody. It's not as much the electric part That I have questions about as much as the propulsion. I have spent hours and hours researching what I should do. I've considered a jet system as apposed to props. I like that the steering and propulsion is all one unit. The boat will be used in shallow water so that could be a plus but jets seem to be less efficient at lower speeds. I know people have taken the power plant out of an outboard and replaced with an electric motor. A trolling motor could work also except for the extreme slow speed. I'm no trying to make a race boat though. Anybody know of a Small inboard outboard style drive unit. Thanks in advance for you answers.
     
  2. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    without knowing your intended use its impossible to give advise.
    -displacement?
    -skimming? I take its a planing design?
    -needed range?

    People (like me anyway) don't hate electric. In fact I would like to love it much more. Its just that it works for very limited applications. You very quickly enter a circle where to be of any use you need more batteries which result in a boat that needs more power due to added weight which results in needing more batteries...
    Energy density is just nowhere near hydrocarbons.

    The financial sense is rarely there either. "fun boats" get used so little that the investment in high tech never pays off in saved fuel.

    Typically electric is sensible for small recreational displacement speed craft which are used in a way that limited range can be lived with. Not much else.

    Prop is more efficient that jet.
    Trolling motor are cheap and easy. Swapping a prop might work but it really depends on your need of power.
     
  3. messabout
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    messabout Senior Member

    Kerosene laid it all out for you Sandy. What he has politely said is: "there ain't no free lunch".

    Tell us more about what your desires and aims are, and perhaps we can be more helpful or encouraging.
     
  4. Sandy1
    Joined: Mar 2015
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    Sandy1 Junior Member

    Thanks for your interests

    The displacement is 550 pounds. The boat is a planing design. I would like around 1 to 4 hours total time. As I said the boat does have to be electric. I again today have been looking at different propulsion systems. My preference is that the motor be on the inside of the boat, so I have been looking at different methods of connecting the motor to the prop and considering the jet still also. That's what I'm really needing help and advise with. I just found this and was trying to find out it's method of propulsion.

    http://go-float.com/models/vector/ Thanks again for your help!
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Torqeedo . . .

    [​IMG]

    About 8 HP and costs more than a gas outboard. They also do inboards, but the smallest is about 40 HP and frankly an inboard in an 8' boat seems silly.
     
  6. FAST FRED
    Joined: Oct 2002
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    FAST FRED Senior Member

    Installing a simple low cost trolling motor in a covered well will do what you need.

    Plaining is out with electric anyway , so sit back & enjoy hull speed.
     
  7. Skyak
    Joined: Jul 2012
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    Skyak Senior Member

    I suspect there is more to your requirements. Local lakes that have electric only restrictions also have an implicit no wake zone. Jet drives are significantly less efficient at low speeds and electric is significantly more costly than internal combustion. There is plenty of expertise here to quantify what it would take to make an electric jet drive but for what it costs the first logical step is make a new boat. You need a realistic understanding of cost/thrust*hour of electric.

    Torqeedo is THE high volume electric boat motor producer -pick the setup that meets your performance needs. Then how do you feel about spending 2 to 3 times as much on a year long project to make a jet drive of that performance?

    Did you have a much cheaper solution in mind? Again using the Torqeedo as a reference I would venture to say that you could do a project that achieved equal or greater performance for less money -with no value assigned to your time and neglecting resale value. As projects go it's good clean fun, but if you are expecting to impress with performance I would say your project would be better off starting with a more efficient displacement mode hull.
     
  8. gonzo
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    gonzo Senior Member

    An 8 foot boat displacing 550 pounds will need a dozen torqueedoes to get it up on a plane. With the expectation of 1 to 4 hours of running, it doesn't seem like it could carry the batteries without sinking.
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A 10 HP Torqeedo will push a 700 pound dinghy to about 17 MPH, which is in full plane mode, assuming it has the bottom shape to get up on plane. I'm fairly sure his "eight foot skimmer wood boat" is a cocktail or similar class hydro, which will get up and scoot, if given enough power. A 10 HP on a Cocktail will get to the low 20's.

    [​IMG]

    The cocktail class typically run of 5 to 8 HP outboards, though usually souped up a bit, so a 10 or 12 HP in reality.
     

  10. gonzo
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    gonzo Senior Member

    I guess I'm behind the time on the power ratings
     
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