prop shrouds

Discussion in 'Boat Design' started by waterwar, Jan 31, 2011.

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  1. waterwar

    waterwar Previous Member

    0Prop shrouds are a type of prop cover.
    These vary in size from small rings and very simple collars to complex shrouds. A very common misconception among non technical people is that the bare propeller is the fastest in the water...
    Well, we don't live in Kansas anymore folks! that's stinking thinking...
    So, if you want to enhance speed and performance and increase your powertrain aspect ratio.
    You better look into advanced designs. Lets look at the USA's
    Navy.Those weapon systems that are of course the fastest objects in the water column:subs and torpedoes.
    The Los Angeles class attack submarines all use a propeller ring.(huge)
    The MK 48 torpedo(USA'a operational to 2025) uses a full shroud around its multiple propellers. Its speed is 120 knots (more or less but it outruns submarines and they are fast!
    If you think the shrouding slows them down you are seriously not thinking very clearly at all. By shrouding the powerful torpedo's propellers it makes them function like a turbine vane in a jet engine and makes the propulsion like that of an underwater jet coming out the rear.

    Thanks for listening curious for replies...

    The advanced engines for powerboats exhibit this growing trend to enhance spreed and performance by shrouds.So I guess 'old school' holdouts will have to relearn the truths of hydrodynamics by being last to the 'ole fishing hole .


    stew
     

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    Last edited: Feb 7, 2011
  2. pistnbroke
    Joined: Jan 2009
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    pistnbroke I try

    yes but its no good shrouding a standard prop you need the ends of the blades shaped to match the shroud .....unless of course its a hire boat and you just want to protect the blades....or surf rescue and you dont want to chop people up ...
     
  3. anthony goodson
    Joined: Mar 2007
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    anthony goodson Senior Member

    A major reason for the shrouding on a submarine's propeller, or more correctly propulsor, is to reduce it's acoustic signature ,which it does ,apart of course from directly astern.
     
  4. waterwar

    waterwar Previous Member

    shrouds

    Actually the cover is there to enhance speed its electric propulsion makes it very quiet indeed but the point is being missed .The weapon is dependent on the cowling to generate the tremendous thrust to race through the water.
    Its a turbine water jet propeller system it would not function without turbine cowling nearly as well the multiple propeller arrangement scheme presents problems if they are inline... starvation of 2 propellers of water stream...

    stew
     
    Last edited: Feb 5, 2011
  5. TeddyDiver
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    TeddyDiver Gollywobbler

    :rolleyes: I was about to write something nasty but I didn't..
     
  6. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    *You got your technology and terminology all wrong.
    *The blades make noise that can be recognized regardless of the engine. Electric driven submarines (diesel on the surface), went out of style a long time ago. Nuclear power is what makes them go now.
    *A turbine water jet has an impeller, not a propeller. They are two different things that you are confusing.
    *A submarine, running completely submerged has a very different operating conditions than a surface vessel.
    *Your smug attitude is rather insulting. If you want to discuss technology in a forum where most people know more than you, it makes you look like a fool.
     
  7. tom28571
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    tom28571 Senior Member

    Is this supposed to be a mystery? What is the difference between this concept and the usual jet impeller? Should be no surprise that a ducted propeller would work. Yamaha makes then for their outboards. The technology is very different from just fitting a ring around a normal propeller though. The whole system, including gears has to be designed for it.
     
  8. gonzo
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    gonzo Senior Member

    Some of us lowly mortals used them on trawlers. Those do make the boat slower but provide more thrust. It all depends on what the goal is. I think we are being let in on some closely guarded government secret technology.
     
  9. tom28571
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    tom28571 Senior Member

    Not so fast Gonzo, the latest submarine technology is self contained cumbustion power with no surface exhaust. Navies are going this way for quietest operation.
     
  10. waterwar

    waterwar Previous Member

    *The blades make noise that can be recognized regardless of the engine. Electric driven submarines (diesel on the surface), went out of style a long time ago. Nuclear power is what makes them go now.*

    That's incorrect the most recent modern submarines are electric engines with diesel and with advanced fuel cell technology. They are formidable and silent and can submerge 30 days at a time, even under way electrically.. Very scary



    My point, I was trying to make: was that enhancing water flow through venturi jet allows a nozzle system to operate at higher levels of efficiency. ie. As it flows out it creates a venturi in controlled circular vortex.. The drag produced by cowling is what must be overcome by the increased boost from venturi..

    stew
     
    Last edited: Feb 6, 2011
  11. michael pierzga
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    michael pierzga Senior Member

    Pickup anything in an enclosed small craft prop nozzle arrangement and you may damage the gear and have a difficult clearing dive. Tunnel bow thrusters are efficient but notoriously difficult to clear .

    Small craft skim along the surface and subs operate deep. different environments, different use...I dont think that you will find the efficiency gain, cost and complexity of a nozzle appealing to small craft operators. .
     
  12. Submarine Tom

    Submarine Tom Previous Member

    waterwar,

    I see by your handle that you are in conflict and confrontatious before you even begin. Your rep points are even in the negative.

    Your "smudge" statements are false and true, depending. Tow boats (tugs) use nozzles (shrouds) for a reason, Human Powered Submarines (HPS) do not, again, for a reason.

    You are a huge, unquestioning fan of them. So what. What is your point? That we are all wrong?

    You waste my time.

    -Tom
     
  13. gonzo
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    gonzo Senior Member

    Tom28571: I thought that self contained combustion was a direct drive or for turbines. Are they charging batteries and running electric motors with it?
     
  14. waterwar

    waterwar Previous Member

    shrouds

    Whoa a little 'touchy' some on this board are I think!
    Actually i don't think my handle is that relevant is it?
    Judging book by the cover?
    The facts still stand about propeller shrouding, it works if you know how to do it.
    I'm sorry if it wastes your time but its the truth and new technology spin off I thought might be of interest to people who are serious about boating

    I had read old threads So I was just trying to clear the air as to applications not by dismissing the request of info on propeller protection as the person had requested. He was told find another beach. Witty replies are funny and amusing... but sometimes if used to dismiss real inquiries they are totally counterproductive!

    Stewart Loeblich
     
    Last edited: Feb 5, 2011

  15. gonzo
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    gonzo Senior Member

    For starters, there is nothing new about it. Secondly, read your original post. You are treating us like we are a bunch of ignoramuses.
     
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