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

  1. Scheny
    Joined: Feb 2012
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    Location: Vienna/Austria

    Scheny Junior Member

    Thx, I have changed the link now to a smaller thumbnail instead. I am not very used to writing in forums and have just now realized the attachment button for pictures ;)
     
  2. I57
    Joined: Feb 2008
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    Location: Melbourne, Australia

    I57 Senior Member

    Andreas
    What sort of drive system are you going to use for the wave interference hull? If you were to use a drive leg would the extra drag affect the performance?

    Ian
     
  3. Scheny
    Joined: Feb 2012
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    Location: Vienna/Austria

    Scheny Junior Member

    As the hull has some sort of a keel, it nearly pushes you for building an internal drivetrain, having the nice sideeffect of reducing drag. The "keel" has a "height" of 13cm on the stern, which suggests to use a 12x12 APC prop (30cm diameter) with a gearing ratio 1.333 times higher than for a 16x16. This gives the boat a nice draft of only 35cm and won´t affect the performance too much. Of course, it is possible to use bigger props too, but in this case, the driveshaft would be in water on a length of 0.5-1 meter, incrementing drag and the draft would also increment by 10cm (4'').

    I plan to use a HTD belt with a 90° twist, as this method is absolutely maintanence and corrosion free and very cheap, as it will use only one custom built part, which can be lasercut very cheap. The whole drivetrain with the best and only new premium parts will cost me only 150€ (but can be built for half or less).

    The highest amount of drag will result from the twin rudder arrangement, but anyone can build a single or dipping ones too. The major goal in research was convenience and not top speed. In my opinion, the advantage of stability, light weight and small storage area is worth to reduce top speed from 15km/h to 12km/h. The idea is to have the performance of a commercial 5m boat at half the dimensions and weight (and only a factor of the price). If there will once be series production, I want it to be as cheap as a series built race bicycle (not a carbon one ;))

    As I said, it will not be the fastest HPB in the world, but I try to make it the best ;)

    Greetings from cold Austria, Andreas
     
  4. u4ea32
    Joined: Nov 2005
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    Location: Los Angeles

    u4ea32 Senior Member

    Dude, it is impossible. Take a high school physics class. Put down the crack pipe.

    I would rather encourage you, but at your level of intellectual development, that is impossible too.
     
  5. Submarine Tom

    Submarine Tom Previous Member

    U4ea32,

    Aren't you being kinda harsh on the guy for trying?

    Let him run with it instead of wasting his energy arguing with you, dude.

    Where about's in LA are you?

    -Tom
     
    1 person likes this.
  6. Dennis A
    Joined: Aug 2009
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    Location: Amersham bucks uk

    Dennis A Junior Member

    Simple right angle drive unit

    I was browsing at the local Axminster tool centre and spotted a angle drive unit that could be used for a bent shaft over the side drive system This is a little lighter than i would like, but I think that it would be fully suitable for those with lower power out puts. It has ball race bearings, hardened pinion gears, 8 mm A/F hex input shaft and 10 mm keyless chuck. The handle holes are on both sides and could be used for fixing. The price quoted was £23.70 which is about 20% of the normally used industrial units.

    Dennis A
     

    Attached Files:

  7. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    I think these are meant for low torque, high rpm power drill applications. Might work for awhile if rapid acceleration/prop weed entanglement etc. can be avoided.

    Porta

     
  8. Submarine Tom

    Submarine Tom Previous Member

    Nice find but didn't Rick W try these and they broke???

    Or is my memory being creative again?

    -Tom
     
  9. Squidly-Diddly
    Joined: Sep 2007
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    Location: SF bay

    Squidly-Diddly Senior Member

    I believe the 'surfing on your own wave was done but USAF's

    B-70 Valkyrie mach 3 bomber.

    No idea if concept could translate to surface vessel.


    It was a shock cone it was surfing on.
     
  10. Jeremy Harris
    Joined: Jun 2009
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    Location: Salisbury, UK

    Jeremy Harris Senior Member

    Dennis, this is the same as the unit that broke on me at Beale Park last year, in the "Cordless Canoe Challenge". Having stripped it to do a post mortem I found that the bevel gears were held to the shaft by tiny steel pins that aren't able to take a lot of torque. They're OK for relatively high rpm, low torque, use, but I'd hesitate to recommend them for driving a large diameter prop.
     
  11. Scheny
    Joined: Feb 2012
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    Location: Vienna/Austria

    Scheny Junior Member

    Hallo David!

    I know that promising -35% sounds somewhat unrealistic, but you have to count in the peripheral values. EVERY boat reduces wave buildup by lengthening the hull, as the angle with which the water is pushed aside gets smaller. This is how the hull length is calculated. I have to confess, that I am too sceptic about promised advantages bigger than -5% from someone new.

    The approach of the displacement glider is something already tested and used since almost 20 years, it has only not been used in such a small boat. Increasing hull length is a somehow two-dimensional approach. The DG-hull cares about pressure distribution in three dimensions. The -35% only apply compared to a boat with the SAME DIMENSIONS AND WEIGHT. If you compare it to a boat like Will`s, with same weight, but twice the length, it will surely have worse characteristics than his.

    As I said, it will not be fastest of any, but the fastest of its size. By the way, i have one master degree in safety relevant electronic engineering (and work in a company involved in your new space program too). For sure, this is not purely physics, but still I am not someone juggling with values too easily handed ;)

    @squiddly-diddly: surfing on its own wave was spoken only literally. That was only a way to explain, how you can imagine the technology.

    Hope I could strengthen your believe in this project a little bit. But to be true, I am also sceptical about the practical top speed, but I am convinced enough, that I have put in already many hundreds of hours.

    Andreas
     
  12. Jeremy Harris
    Joined: Jun 2009
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    Location: Salisbury, UK

    Jeremy Harris Senior Member

    Andreas,

    The key issue here is that the power needed to push a small boat through the water at low speed is almost entirely dominated by viscous drag (skin friction). Wave-making drag plays virtually no part in contributing to low speed drag at all, unless the boat waterline length is very short.

    The key to minimising the power requirement (which is critical when you only have around 100 watts of power available for propulsion) is to minimise the wetted area for the length of hull needed to get the speed you're looking for. There are compromises, driven by things like ease of construction and stability, that mean that the ideal long, narrow, semicircular hull (which would give lowest wetted area as a rule) may not be ideal, but to go for a design such as you have suggested, where the wetted area is very high, seems a poor choice for such a low powered craft.

    There is a good reason that pretty much all the successful pedal powered craft are converging on the same general hull form, long, narrow stabilised mono hulls or sometimes twin hulls. That reason is to do with efficiency, as many experiments have shown that hull form to need the least amount of power for a given speed.
     
  13. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    Scheny:

    Maybe the 35% reduction applies to high speed powered boats, something like a jet ski?

    Anyway if it works at 100 watts, I want one!

    Porta


     
  14. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    Hi, Jeremy:

    Do you think using larger hardened pins would help, at least for your canoe challenge? Or is the plastic? housing likely to give way and let the hardened gears slip their mesh?

    Porta

     

  15. Submarine Tom

    Submarine Tom Previous Member

    There you go, thanks Jeremy, I knew somebody broke one. Could the pins be bored out larger and replaced with lower grad?

    Jeremy, isn't Rick's world record breaking boat quite a contradiction to your last post (#1242)? Cat, square cross-section hulls, huge wetted surface area...?

    Perhaps it's getting away from "low speed".

    -Tom
     
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