Water jet active stabilizers

Discussion in 'Hydrodynamics and Aerodynamics' started by jjj, May 20, 2020.

  1. jjj
    Joined: May 2020
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    Location: UK

    jjj New Member

    This is probably a naive question, but active stabilization using fins is now quite common, but has the downside that the protruding fins can become a liability in a collision, ripping of an even resulting in a hole in the hull (as well as the more mundane constant additional drag forces).

    I was curious why no systems use water jets (e.g. the jet would be facing down on each side of the boat to provide a right forcing, with a pump taking water from on side and pumping to the other side to generating a righting force). Is it just impossible to get this to be efficient?
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    I don't know if it is a valid comparison, but I assume some of the righting action of stabilizers is owed to the forward motion of the boat, but with water jets, it would be more akin to a helicopter versus the aeroplane, which generates lift by forward motion.
     
  3. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    Some? More like: all.
    If it wasn't for the "forward motion of the boat" there would be no water flow over the stabilizer wing.
    No flow, no lift, positive or negative, no "righting action".

    JJJ,

    Welcome to the forum.

    Not sure what you mean here. Would you clarify?

    Your idea makes me think of rocket thrusters on space vehicles.

    What size boats are you thinking of?
    How would the waterjets be powered?
    Instant on, maybe electric?

    Trim-tabs on some smaller boats are less susceptible to damage and don't create much drag.
    Not sure if they are used in active roll stabilization though.
    This is what you're proposing is it, roll control?

    Cheers
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    I'm happy to hear all views, but I doubt it is "all"
     
  5. gonzo
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    gonzo Senior Member

    Fins are very effective when the vessel is moving. Otherwise, gyroscope stabilizers are hard to beat. Major drawbacks to waterjets, are noise, water splashing, clogging with debris and turbulence that creates added drag.
     
  6. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    Sounds problematic, would take a lot of power to move enough water to be effective, especially in heavy seas.
    I agree with Gonzo, gyrostabilizers are the cleanest, quietest, non intrusive (non protrusive too!) solution, and are still effective when vessel is stationary.
    How about gyro controlled hydraulic trim tabs in the prop wash to counter roll?
     
  7. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Please help me understand where the rest of the "righting action" comes from if not from water-flow-induced lift, positive or negative, over the stabilizer wing.
    Thanking you in advance.
     
  8. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    While in morion the righting force is overwhelming provided by lift.

    While at rest there is a small stabilizing effect in the same manner that "flopper stoppers" work for smaller craft. Resistance to vertical movement.
     
    Barry likes this.

  9. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    Ah, the penny drops, thank you.
     
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