Best custom prop maker?

Discussion in 'Propulsion' started by RainerJ, Feb 24, 2009.

  1. RainerJ
    Joined: Feb 2009
    Posts: 3
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    Location: New Jersey

    RainerJ New Member

    I'm working on a special electric boat project, and our team needs a company to get a prop to fit a Konny Motors lower unit. (it's an oddball straight shaft w/pin and diameter of .59", but we can machine spacers)

    Our biggest constraints is we need counter-rotating props (two shafts on the boat), and something around 7"DIAx8.5" dimensions for the prop. Obviously, we need something typically available in hydro racing since they don't vent exhaust through the center hub.

    Any recommendations?

  2. Guest625101138

    Guest625101138 Previous Member

    I know a firm that can mill props to my design but they are not cheap.

    What are the prop operating conditions? Why counter rotating? Who has done you drive design?

    Rick W
  3. RainerJ
    Joined: Feb 2009
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    Location: New Jersey

    RainerJ New Member

    By counter rotating, I mean I need both a right hand and left hand prop, since we have two outboards.

    I'm in a group that is designing a electric boat, and we would like to punch out the most performance we can for a 'drag race.' of the available power we have. The drive train is custom, and being built right now. We don't have the capabilities (see: 5 axis milling machine) to make our own props.

    Also, I wanna add that these are fairly low HP motors (2x15HP), but this entire endeavor is an experiment. I promise I'll post the results of the progress we've made so far once I get some photos.
  4. Guest625101138

    Guest625101138 Previous Member

    What distance will the race cover. Is acceleration important or will you be operating close to design speed most of the time?

    Are you using foils or it it just a planing hull? What weight?

    It is not very difficult to make a prop from stainless flat bar if you can weld proficiently. I have a detailed procedure for it but the prop has to be designed to suit.

    My initial impression is that a 7X8 prop will give low efficiency. Is there any draft constraint?

  5. RainerJ
    Joined: Feb 2009
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    Location: New Jersey

    RainerJ New Member

    Rick - thanks for all your questions. I kinda forget about all these crucial details because our group has been working so tightly with them and just assume they're obvious now.


    Ideally, yes, getting to top speed is the most important. We're more or less looking at draining these batteries during the demonstration. (as such, we only carry a limited amount of batteries)

    No foils yet. It's a planing hull. The whole kit and kaboodle will weigh 475lbs with pilot.

    Anyway - Our team is just looking for custom prop makers that others have had business with. We're happy with the analysis done so far, and we're looking to get on the water.
  6. Guest625101138

    Guest625101138 Previous Member

    With that sort of weight and power you may get good results from a surface prop. There are some threads here on surface props.

    When I get some time this weekend I will look at what could be possible with the best submerged prop.

    Rick W
  7. apex1

    apex1 Guest

    ROLLA ........................

    But it will cost you half a house.
  8. Guest625101138

    Guest625101138 Previous Member

    I did the analysis for submerged props.

    I have attached the Savitsky prediction for power and thrust that the hull requires. There is also the JavaProp design for the props. It indicates the top speed achieved with this set up would be around 42kts. The props gives 86% efficiency and power required is 20kW leaving a little in reserve to cater for windage.

    These props could be hand fabricated in about 1 day.

    Could possibly get higher efficiency if the best foil section was used.

    Rick W

    Attached Files:

  9. sparky_wap
    Joined: Mar 2008
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    Location: Suffolk, VA USA

    sparky_wap Junior Member

    I have a set of...

    8 X 8 props. They are made of brass and are three blade round ear units bored for 0.75" shafts. I thought I would try them out behind a pair of counter rotating direct drive series forklift pump motors (10-15 HP) sometime in the future. The cost of light LiFePo4 batteries has held me up from that project.

    I also have several left hand 6 3/4" diameter two blade stainless racing props with a pitch from 10.5" to over 12". Could these be reworked to the opposite pitch?

    I tried a 7" X 10" surface prop but the boat was too heavy(700 lbs) to plane.
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