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Discussion in 'Boat Design' started by Guest625101138, Jul 14, 2008.

  1. spidennis
    Joined: Feb 2007
    Posts: 519
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    Location: south padre island, texas

    spidennis Chief Sawdust Sweeper

    I can understand it, it's like some of my videos, it's not meant to be a documentary, just a quick visual aid. I do wish he was still here though to explain ........
     
  2. Submarine Tom

    Submarine Tom Previous Member

    But I thought he had a web-site, no?

    -Tom
     
  3. spidennis
    Joined: Feb 2007
    Posts: 519
    Likes: 11, Points: 0, Legacy Rep: 124
    Location: south padre island, texas

    spidennis Chief Sawdust Sweeper

  4. Submarine Tom

    Submarine Tom Previous Member

    Okidokie.

    Thanks.

    -Tom
     
  5. portacruise
    Joined: Jun 2009
    Posts: 1,134
    Likes: 39, Points: 48, Legacy Rep: 218
    Location: USA

    portacruise Senior Member

    Rick has answered a couple of questions about his CF prop on the hpv-boats forum. You can access the archives through this page but it is a couple of months behind.

    http://hupi.org/cgi-bin/mailman/listinfo/hpv-boats

    You can sign up to get his latest messages (yesterday's posting).

    Porta

     
  6. Scheny
    Joined: Feb 2012
    Posts: 72
    Likes: 5, Points: 0, Legacy Rep: 47
    Location: Vienna/Austria

    Scheny Junior Member

    I have been checking on the prop from Torqeedo. They say, that it takes 180W at 10kph (5.5kt) and 1200rpm. The rpm are a bit high, but this might be the perfect prop, if you plan to build a boat using a toothed belt.

    At 1200rpm the torque is so low, that a belt with a small pitch and therefore low losses can be used. I think, that I will give it a try.

    The prop has a diameter of 200mm, which makes it perfect for shallow water. I have calculated the losses of a 200mm compared to 405mm of a 16x16 prop and I found out, that efficiency is about the same, if you do not request too much thrust.

    So in my opinion, a stabilized monohull or catamaran would have the same efficiency, if you are willing to limit speed to cadence. If you are going for thrust, like coach Dave, the "Texas sized" prop surely will be the better choice.
     
  7. Jeremy Harris
    Joined: Jun 2009
    Posts: 978
    Likes: 59, Points: 28, Legacy Rep: 711
    Location: Salisbury, UK

    Jeremy Harris Senior Member


    I don't know how you compared the Torqeedo prop to a larger diameter, higher aspect ratio prop, but can say with certainty that the latter will be more efficient. The Torqeedo props are reasonably good, but still poor when compared to the sort of high performance props we're using. Like all commercial manufacturers, Torqeedo have made compromises in the design, which reduce efficiency.

    Firstly, propellers need to be accurately matched to the hull resistance, something that Torqeedo cannot do, because they are marketing a general purpose drive unit that will be used on a wide range of hull types. They therefore pick a prop design that will work reasonably well over a wide range of conditions, which inevitably means that it works less well than an optimised propeller.

    Secondly, Torqeedo designed their propeller to shed weed, because weed and plastic bag fouling is an important characteristic when marketing a commercial product. Unfortunately, as we've found out from experiment, making a fixed prop that has high efficiency makes it more susceptible to weed fouling. If the blades are swept to reduce fouling risk then the efficiency reduces, both because of the change in blade shape and also because of the reduced torsional stiffness of the blade, which tends to make it de-pitch under load.

    The most accurate modelling programme that I've used (and which people like Rick Willoughby and others have confirmed as being accurate) is Javaprop. If you put the Torqeedo propeller parameters into Javaprop and then compare them with those for something like a model aircraft propeller of a larger diameter (obviously at a lower RPM) then you will see that the Torqeedo prop compromises impact on performance quite significantly. The Torqeedo propellers are also quite expensive, IIRC.
     
  8. spidennis
    Joined: Feb 2007
    Posts: 519
    Likes: 11, Points: 0, Legacy Rep: 124
    Location: south padre island, texas

    spidennis Chief Sawdust Sweeper

    Thanks Porta, I got signed up!
     
  9. Submarine Tom

    Submarine Tom Previous Member

    Ya, I got signed up too but didn't get anywhere...

    -Tom

    Scheny,

    I've used JavaProp and can second Jeremy's post.

    -Tom
     
  10. spidennis
    Joined: Feb 2007
    Posts: 519
    Likes: 11, Points: 0, Legacy Rep: 124
    Location: south padre island, texas

    spidennis Chief Sawdust Sweeper

    I signed up and already got my first digest, found rick's email and sent him off a few questions.
     
  11. Submarine Tom

    Submarine Tom Previous Member

    I'll try again.

    Thanks.

    -Tom
     
  12. Coach Dave
    Joined: Jun 2011
    Posts: 70
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    Location: Malabar, FL

    Coach Dave Junior Member

    Here is an example of a heavy boat (Peccadillo 8 tons), low speed, high thrust using a pair of 30x20E props. When the wind died down they put a crew member on the pedals at the back of each hull to get a 1 knot advantage over their competition.

    http://www.sail-world.com/photo.cfm?NID=82737&Pid=136037&flash=&width=1200

    Here is a link for the prop

    http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=8293

    The Peccadillo won the Australian Three Peaks Race in 2011. Here are Rick Willoughby's comments:

    "The win was due primarily to sailing ability. They managed a
    slightly faster trip using the thrusters when the wind died in the
    Derwent River on the final sailing leg.

    The drive legs are folded up with the big prop on the back of the
    seat. The thrusters were secured in this place for the whole race.

    Charles said that during the pre race testing and up the Derwent two
    pedalers could hold 2.4 to to 2.5kts working on 30 minute rotation.
    The other boats could hold about 1.5 knots using oars."
     
  13. GMR
    Joined: Sep 2011
    Posts: 54
    Likes: 1, Points: 0, Legacy Rep: 22
    Location: Nova Scotia

    GMR Junior Member

    Hi 157,

    Ian, are you using the outriggers from your previous boat on the new one as well , or building new ones?

    Thanks, Glen
     
  14. joco
    Joined: Nov 2009
    Posts: 61
    Likes: 1, Points: 0, Legacy Rep: 18
    Location: ottawa/ontario

    joco Junior Member


  15. Jeremy Harris
    Joined: Jun 2009
    Posts: 978
    Likes: 59, Points: 28, Legacy Rep: 711
    Location: Salisbury, UK

    Jeremy Harris Senior Member

    The flexible drive shaft will soak up a lot of power, reducing efficiency a fair bit. I experimented with a drill flex drive and found it used around 10% of the available power. Add in that the unit linked to has two right angle gearboxes plus a toothed belt drive and I'd suggest it's losing around 20% of the available power in the drive system.

    It does have the advantage of being fairly simple to install and use, though, and could be fitted to a fairly wide range of boats pretty easily, and without making holes in the hull.

    Overall I suspect it's probably on a par with the Hobie Mirage in terms of efficiency, maybe a bit less.
     
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