Power Required

Discussion in 'Props' started by Asleep Helmsman, Jan 5, 2010.

  1. kistinie
    Joined: Aug 2007
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    Location: france

    kistinie Hybrid corsair

    The target is a propulsion Pod and a Generator powered by fuel. Any fuel are possible.
    Electricity is the main source of energy aboard.

    About fuels, i only look at their global effect, time to produce and cost of production.

    I use all with pleasure.

    My energy
    Since always, i walk a lot, love bikes, getting older, or just not to smell like indiana jones when going to a meeting, i love to have an electric motor helping me. 500W is to have Lance Amstrong on you bike, plus you of course, for 50 Km.

    Wind
    I sail since i am 12, teach since 18Y, last time was 2008 Club med Corsica for 2 month, just for the love of sailing and transmitting it. (Paid 700€/month, but with many side advantages, ;-), i admit)
    I love race multihulls, love single handing.

    Devil's gift ;-)
    I love Gasoline, petrol, oil, Toluene, N²O...in a Lotus seven or any light car.
    I have raced cars, still love engines and new cars.
    I would love a Tesla or the future Hybrid Aston M.
    A Tesla is 240 miles std driving, up to 310 miles in eco race challenge, is also a 0-60 in 4 seconds commuting toy.

    But
    As time goes i got sick with grease, oil, smell, noise, so stopped racing keeping just a few car i seldom use now. I took on me to achieve that, as i am still having great fun overtaking new expensive cars with old junks.

    I stopped and then decided to put my money in clean building and smart boats. Another reason was, respect, for those that i was polluting with noise and smokes, where jet ski is a kind of Himalayas, and by respect for the environment.
    When i can, i walk, i ride a bike, even a Speed trike, tadpole, i will electrify this year with swiss friends.

    I go more and more toward faster renewable resources, for a scale time reason. Biogaze or biofuel, all renewable energy are produced in "week" time, extracted oil in million of "week" time

    Such time paradox to happy leave with... only a commando trained Buddhist can.


    The other problem is, that, mixing sea life, and oil, makes me puck, just like all sea life does puck with oil.


    I keep a fuel driven generator as we need to keep a link with oil, for a global question of inertia. But at sea, NO oil is the target to go NOW.



    I' building two products:
    -An outside caged motor, Pod. reversible for regeneration.
    -Generator, alternative fuels as aid or solo, co-generation where possible.


    5 Kw Pod thruster and 5 Kw generator, both using latest EM design.

    Both made to be affordable.

    Why 5Kw ?
    Because it is my perfect need, for a 40 feet light sailing boats. 5kw used as i planed, is more than needed for an under 3T trimaran.
    Because it is the lowest common need to target a world mass market. An estimated equivalent, in term of use, of the 9 to 20 HP segment.
    And many other "because" of course.

    Prototypes are for my boat. They are fully home made, mostly from used items to lower cost and demonstrate it is reproducible now.
    A commercial version is not programmed yet as their first purpose is to power Wingover for the research projects she is dedicated to.



    As a conclusion, i just try to be coherent with me, mankind, and earth. A simple motivation can be long to explain.



    -----------------------------
    Please, note, that the links to illustrate this text, are here to help visualize what i talk about. i'm not the tall guy on the left of the picture :)
     
  2. Asleep Helmsman
    Joined: Jul 2008
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    Asleep Helmsman Senior Member

    You have an interesting imagination Kistinie.
     
  3. Asleep Helmsman
    Joined: Jul 2008
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    Asleep Helmsman Senior Member

    Ok now, back to the races.
    I need any info on prop design, you guys have the time to tell me.

    I'm leaning towards a large diameter (ratio wise) and a speed range of 1-8 knots, with the majority of the cruising at 2 knots, and deep enough to avoid surface interference of any kind.
    .
     
  4. Guest625101138

    Guest625101138 Previous Member

    Javaprop is a good place to start. Set the options to suit water. Choose the E193 foil at 100,000 Re# and 0 degrees for the four points on the foils page. On the design page set blades to 2, revs to say 600, diameter to .35, hub to .04, speed to 4m/s and resistance to 50N on the design page. Then press design. You can view the prop shape in the geometry. You can play around diameter, AofA and rpm to see how things change.

    You need a prop with a chord of about 30mm to have adequate strength.

    Using that prop you can set the rpm value and go to the analysis page to see the thrust at various speed for that rpm. Use the cube function to determine drag at at other speeds based on 50N at 4m/s.

    This thread shows how you can fabricate a prop very quickly:
    http://www.boatdesign.net/forums/props/seagull-prop-cat-racer-29910.html
    Or you can use one of the output options with JavaProp to produce a milling machine input from.

    Post questions if you do not understand what JavaProp has produced.

    There are empirical curves for props. The most commonly used ones are the Wageningen B series. It is a messy process full of nautical jargon that will take you days to understand. None of the props tested are suited for such a light loading though unless you are prepared to throw away heaps of power and run a small diameter prop.

    Rick W
     
  5. Asleep Helmsman
    Joined: Jul 2008
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    Asleep Helmsman Senior Member

    Ok Rick, this weekend it's back to props. I got the hull done this last week so I will have many prop questions.
    For instance, is anyone familiar with Rice ducts or better ones?

    I intend to have the prop ducted for all kinds of reasons, but mainly protection and static prop effectiveness. Prop efficiency at zero velocity will end up being one of the major considerations.
     
  6. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Prop efficency (eta) at zero velocity is always identically equal to zero....i.e. no work is being done so 0/anything = 0. What you are looking to do is to maximize bollard thrust, and that is a very different prop from a free running design. BTW, ducting a prop in this circumstance does not make for better efficency overall or improved power usage.

    See this thread...

    http://www.boatdesign.net/forums/education/propulsion-kort-nozzle-4525.html

    and this one..

    http://www.boatdesign.net/forums/education/just-question-5547.html
     
  7. Asleep Helmsman
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    Asleep Helmsman Senior Member

    The very first post seems to support that ducting increases power at "virtually 0 hull velocity"

    Many many thousands of times I have engage the gears on a yacht and watched a large swirl materialize and the boat suddenly move. So I guess you are arguing semantics.

    There is a huge body of evidence for the use of ducts at near 0 speeds. Your own post seem to be supporting this.

    The question is:

    Does anyone have any first hand knowledge of Rice nozzle designs compared to Kurt?

    The Australian guys claim a 10% or so increase.

    One last thing the link you supplied seems to be malfunctioning.

    But thank you for giving me the correct words to look up.
     
  8. Guest625101138

    Guest625101138 Previous Member

    The only good reason for anything around the prop is as a guard unless you go back to the ridiculously small diameter you posted in the first post 25 to 30mm. Ducting would certainly be beneficial for a tiny prop if you could make blades strong enough to handle the loads.

    Ducting the 300mm prop in the original case I looked at that gave the 230W could result in a saving to induced drag of up 7W while a nicely streamlined duct and supports would cost about 25W in extra drag.

    Note that my drag allowance in my original post included some allowance for appendages so even with ducting (really a prop guard) my original 230W is still reasonable.

    Rick W
     
  9. Asleep Helmsman
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    Asleep Helmsman Senior Member

    I'm assuming you mean at 8 knots. I'm more concerned about maneuverability at near zero hull speeds. This UUV need only operate for 8 hr at 2 knots to qualify for consideration. We established that goal would be met at the very beginning. Since then other considerations are taking precedence.

    As you said the props will need to be protected anyway, so why not utilize the most efficient method. Maneuverability to hold station will be paramount, which means large amounts of trust at low hull speeds. And lastly, most side scan sonar activity takes place below 3 knots anyway. The 8 knot flank speed is there merely as a reference.

    I’m building this on my CNC mill so unusual shapes will not really be any more difficult to construct. I might as well do the best design possible.
     
  10. Guest625101138

    Guest625101138 Previous Member

    Yes - My first hand experience is with tugs - just operationally; not a design perspective. Those original (1982) tugs have since been replaced with similar sized tugs rated at 67t bollard pull and fitted with full 360 degree azimuthing nozzles rather than the steerable nozzles.

    Kort nozzles are beneficial on tugs and other applications where the propeller blades are heavily loaded. The losses to induced drag can be eliminated with a prop matched to the nozzle.

    Steerable or full 360 azimuthing nozzles also increase the proportion of flow redirected for off-line thrust compared with a rudder. A steerable nozzle that avoids a rudder eliminates losses to a rudder.

    Rick W
     

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  11. Asleep Helmsman
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    Asleep Helmsman Senior Member

    Rick,
    Thanks for taking the time to provide so much usefull information.

    I probably should have been more clear from the beginning. My intension is to use multiple vectered props and no rudders or dive planes.



    Have you heard anything about the Rice designs compared to Kurt?
     
  12. Guest625101138

    Guest625101138 Previous Member

    Yes of course - that is what you requested in the original post. If you want to do that speed at any time then you need to ensure the installed power will meet it.

    If you want an economic cruise at 2kts then that could be a design point. The ducting is still only a guard. The drag reduces so the prop loading is still low.

    Your duct could provide convenient points for attaching rudders and elevators.

    Rick W
     
  13. Asleep Helmsman
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    Asleep Helmsman Senior Member

    I wanted to find out what it would take to get a top speed, in terms of motors, in case the need arose to outrun unfriendly divers or something, but the crusing speed will be around 2 to 3 knots. Acceleration, and sterring within confined space, is going to be important though, so the extra power will be nice to have.

    The motors are perminent magnet digitally controlled bruchless DC, that only use as much power as they need, so designing for extra top speed doesn"t severely reduce batery life.
     
  14. Guest625101138

    Guest625101138 Previous Member

    My only first hand experience is with Kort nozzles. I have looked over the Rice design and believe they would be advantageous over a simple nozzle near a particular design speed. I believe they aim to have the minimum drag nozzle at the velocity ratio relating to the design speed. The velocity ratio could be at zero boat speed if bollard pull was the main consideration.

    There is discussion here and a link to Rice at post #9:
    http://www.boatdesign.net/forums/propulsion/caged-propellers-26639.html


    I get the impression you are now thinking along the lines of multiple jets. Once you get into ducting and redirecting flows you bring in considerable inefficiencies over an open propeller. All those surfaces increase the wetted area and some of them will experience high velocity flows.

    Rick W
     

  15. Asleep Helmsman
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    Asleep Helmsman Senior Member

    Actually from the vey beginning I was thinking multiple trust. I just wanted to establish a baseline. 8 knots single propeller is a great starting point. But we are looking into hydrogen fuel cells and whatever the most advanced lithiom/whoknows batteries so functionallity and energy conservation are somewhat in conflict.

    As you said fuel consuption reduces with the cube of speed. So the question is will a ducted 12" X 12" prop with a 250 watt motor attached to it pull harder than one without. And at 4 knots, which one will answer an all stop command from the computer faster.
     
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