dory catamaran hull

Discussion in 'Multihulls' started by frank smith, Feb 2, 2010.

  1. Chris Ostlind

    Chris Ostlind Previous Member


    So if water doesn't shape stone for optimal flow, then what shape is it seeking.. a non-optimal flow condition? Really, that's the answer here?

    Do keep in mind that even the harder, included, stone types will eventually yield to the power of the water. All of it will go away to a smooth, organic shape in favor of that power.
     
  2. TollyWally
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    TollyWally Senior Member

    Water isn't seeking a shape for optimum flow it is merely running by. For the most part the stone is not stationary it moves around while the water is machining it to shape. When it it stationary the form it takes is greatly influenced by the surface hardness. A soft pocket will form a depression that further influences the flow that influences the shape etc. If your organic theory of water forming perfect shapes was true then rivers would be far more uniform. Another example. To get an optimum underwater hull shape for minimal resistance you could saw the rough shape bounded by the physical dimensions needed out of a giant bar of soap and place it in a correctly scaled flow of water.
     
  3. bruceb
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    bruceb Senior Member

    shapes

    Chris, only one of those is a race car, and it has some very hard edges- the rest are a production based class and have to use the body shape of the current production car. Good luck with the 62 356- great cars, I have owned four of them. Stones in a stream have more in common with a water/abrasive cutter than anything else and are usually shaped by what was just up-stream of them. Water would prefer to go in a straight line- always. Trying to get back on the thread:rolleyes: There seems to be good knowledge on boats that move at less than hull speed >10 kts for most of us, or more than 18 kts- usually starting to plane, but it is the in between that doesn't seem very well quantified. 12-15 kts is slow for a non-displacement power boat and fast for most sail boats, but it is the range that many of us are interested in. Pushing the envelope:) Any shape can be powered up to "go", sail or power, but to go efficiently is the real question. Bruce
     
  4. Richard Woods
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    Richard Woods Woods Designs

    I have driven cars for a total of less than 500 miles in the last 10 years. So that probably makes me an expert in car design :D (But I have sailed catamarans over 20,000 miles in the same period)

    Getting right back on topic:

    The original question was whether a dory shaped hull was suitable for a relatively low speed (12knot), heavy (8000lb), 34ft catamaran houseboat (10ft x 20ft living space)

    answer - yes

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  5. Chris Ostlind

    Chris Ostlind Previous Member


    Coulda fooled me then, Bruce. I have this visual problem of seeing them running the Sebring 12 and the Daytona 24 as well as this last weekend at Long Beach, right along with the Spyder on the very same track. One seat inside, interior stripped, roll cage in place and all important fasteners safety wired.

    The dudes who got out of the cars were all fancied-up with fire suits, gloves, balaclavas and helmets. They took flags to start and to finish and took instructions over team radios for stops, and strategy. The kinda stuff one dons to run to the store for a quart of milk.

    Yeah, I'd have to agree that they're not race cars at all. All the production classes in USSA, not race cars. The Yamaha 350's I used to run, which were no longer street legal, also not race bikes.

    Come on, Bud.
     
  6. Chris Ostlind

    Chris Ostlind Previous Member

    So, gravity and topography have no place in this scenario, do they? And seeking the path of least resistance is somewhere out of left field?

    Come on, Tolly.
     
  7. Chris Ostlind

    Chris Ostlind Previous Member

    Actually, the original question was...

    "In looking at catamaran hulls i see many different ways to go about their design.
    I am interested in a simple dory hull form and wonder what the disadvantages of the hull form are."

    Very clearly, that is not, "are they suitable?", unless one is feeling very gifted with abstract interpretation. Certainly an engineer wouldn't draw the conclusion in error.

    Some of the answers in this jumble have worked so incredibly hard to ignore the obvious about suitable hull form, which one would think is somewhere out there around mile 0 at sea. Well before one leaves the marina. ;-)

    It has been fun, though.
     
  8. TollyWally
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    TollyWally Senior Member

    Chris,
    I'm not going to argue with you, your theory is unconvincing to me. I suggest we move on. Your remarks to Bruce indicate that you do not understand his position although it is clear you disagree.

    FWIW if the Yamaha 350's you refer to were the legendary RD 350's built in the 70's then it is all semantics. They had lights and plates but to call those street bikes is a bit of a stretch. Grenades maybe. An awful lot of those ended up as track bikes. Their reputation for speed and seized motors made for dirt cheap go fast. At the track, rather experimental exhaust tuning coupled with loose tech standards, at least around these parts, made for spectacular thermal induced skid marks.

    Back to boats
    Bruce,
    Any guesses on horsepower requirements? I'm guessing at these speeds you can get away with bigger slower wheels.
     
  9. guzzis3
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    guzzis3 Senior Member

    I never cease to be amazed at how ready some of you are to start and continue an argument, especially a pointless one.

    A lady frind of mine came up with a perfect term for this sort of thing many years ago, ant *******. Focusing in on something virtually irrelevant and thus paying less attention than required to other aspects.

    You start with a criteria and you design to meet it. The dory hull will do. It may not be the very best result but it will work fine provided it is sensibly designed. Get over it.

    And don't get me started on porsches..it always kills me how people substitute "driver's car" for "handles like a pig". I know a chap who picked up a ferrari V8 cheap and slotted it into a westfield. THAT is a drivers car.

    Me, I drive a subaru....
     
  10. TollyWally
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    TollyWally Senior Member

    LOL,
    "Me, I drive a subaru...."

    What model? I bought one a few years back as a pleasant practical rig with a bit of utility value. When it was time to swap out the clutch I went to the net and found some forums. I was looking for tech tips and tricks. I had a vague idea Subaru was interested in rallying etc. but had thought little of it,

    OMG, I had no idea what those kids were doing hopping those cars up. Crazy stuff, I was fascinated. A whole radical hot rod culture existing beneath my radar. Long story short, I modified my tire pressures fore and aft. I ended up with a completely different vehicle.
     
  11. bruceb
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    bruceb Senior Member

    details

    Tolly, the latest GT3 you can buy over the counter_ really street legal, has 500hp at 8800rpm. I am sure the race teams find some more:rolleyes: The Ferrari 430s are giving them a hard time. I run 335/17s on a street turbo, they really help keep the engine behind me:cool: The "hot" Subarus have the same kind of performance with a lot more finesse and less tire smoke:)
     
  12. ancient kayaker
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    ancient kayaker aka Terry Haines

    Since you asked ...

    Water seeks the easiest path short-term but this evolves to a minimum energy configuration over a long period. The result of this can be seen in the semi-sinusoidal meanderings of a stream over it's flood plain. The shape that a fixed, fully-immersed rock develops when worn by a more or less consistent water flow is not necessarily related to the optimum shape of a hull at the surface. Check submarine shapes.

    My own meanderings are rarely if ever sinusoidal, but I digress. Hm ... don't we all?

    Damn, it's late ...
     
  13. TollyWally
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    TollyWally Senior Member

    Bruce,
    You sound like a fun guy to hang out with. We might have died doing it in high school at the peak of invincibility. :) I'd like to see some action pics someday. Not really sure a 12 knot dory thread is the right place. I'm still curious about the power requirements of a 8000# 12 knot boat.
     
  14. Alex.A
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    Alex.A Senior Member

    If water seeks the straightest path/least resistance - why aren't all huuls straight sided? Be like an american car - fast in a straight line but suck through the corners?
     

  15. ancient kayaker
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    ancient kayaker aka Terry Haines

    With good ground effects and enough speed any car can be made to suck which will allow it to go faster through corners. Left alone water will fall straight down, but so will anything else. We're obsessing again ...
     
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