Magnetohydrodynamics and Waterjet Engines.

Discussion in 'Hydrodynamics and Aerodynamics' started by SET Project, Apr 20, 2022.

  1. SET Project
    Joined: Dec 2021
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    SET Project Junior Member

    Hi,

    I was curious to know what aspiring engineers and navigators thought about renewed forms of propulsion. Especially, Magnetohydrodynamics and Waterjet engines.

    I know that as of right now these propulsion systems are found in small vessels (ie tugboats).
    But, do you (in a general sense) think that Waterjet engines could find their way onto much bigger vessels such as cargo ships ? And would Magnetohydrodynamics find its place as a renewed driving force given the technological revolution we're in ?

    Thanks
    Antoine / SET Project Founder
     
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  2. bajansailor
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    bajansailor Marine Surveyor

    For ships, a large, relatively slow turning propeller is always going to be more efficient than any water jet.
    Hence I do not think you will find water jets on cargo ships any time soon.
     
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  3. Ad Hoc
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    Ad Hoc Naval Architect

    Bajansailor gave you the shortened version answer - no.
    Waterjets are not designed to be slow turning, in that sense, like a big slow turning prop on a tanker etc. .

    Waterjets are ostensibly for high speed operations.
    If you want a prop, in a tunnel, so to speak, just use a classical Kort nozzle.
     
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  4. Will Gilmore
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    Will Gilmore Senior Member

  5. bajansailor
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    bajansailor Marine Surveyor

    Here is a good example (or two examples rather).

    Cat tug stern view.jpg
     
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  6. messabout
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    messabout Senior Member

    ^Pretty props. They appear to have lots of washout. The rudders have something akin to flow straighteners with a slight negative incidence angle. The designer was thinking every minute it would seem........or maybe I am seeing things that are not there. That happens, especially when I have been into the sauce.
     
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  7. bajansailor
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    bajansailor Marine Surveyor

    I think that you are spot on there - I know the designer of this tug, and this is an accurate description.
    BTW, the recent acceptance sea trials on this tug were successful, and exceeded the original design expectations.
     
  8. SET Project
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    SET Project Junior Member

    Interesting. The propellers are fairly big, this will give good momentum once the ship is given a route.
    What is the LWL size for this vessel ? And what is the main source of power to get the propellers going ?
     
  9. bajansailor
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    bajansailor Marine Surveyor

    The LWL of this catamaran tug is about 9 metres. She has a pair of Yanmar 6 cylinder 140 kw diesels with high reduction gearboxes driving these propellers giving her an impressive bollard pull of 6 tonnes.

    Here is a photo of her while she was under construction -

    Cat tug construction 8.jpg
     
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  10. SET Project
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    SET Project Junior Member

    Thank you for the paper, I will give it a read thru. I had also read the Yamato-1 proof of concept, and it is an incredible project.
    My next step is to create a MHD system to make my conclusions. The concept of MHD is super interesting and I think it can become a useful tool for ships.
     
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  11. jehardiman
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    jehardiman Senior Member

    Even though I'm not an aspiring engineer, I have designed and analyzed many propulsion systems. I too concur with sentiment that waterjet and MHD are specialty niche systems. From your website I'm not sure how far along you are in coursework at the University of Avignon, but eventually in engineering and/or physics you will run into the Square-Cube Law. Square–cube law - Wikipedia https://en.wikipedia.org/wiki/Square%E2%80%93cube_law The Square-Cube Law is why merchant ships have always increased in size over history. The physics of the Square-Cube Law drives the engineering and economics of scale. And this includes the propulsor.
    Generally, for marine propulsion systems operating in the water, thrust is produced by achieving a pressure difference over an area by changing the velocity of a mass of water. Given material limits of existing (and near term foreseeable) economically producible materials, the Square-Cube Law limits either the pressure or the size available to produce thrust. This is why 22 knot 141,000 DWT Neopanamax merchant ships have 100,000 HP and a 10m propeller while a 47 knot 3,500 GT ferry also have 100,000 HP but four 2m diameter waterjets or why Yamato-1 could only achieve 8 knots because of the flux packing factor of her drives.
    For a discussion of props vs waterjets see this post.
    What is world's biggest planning hull boat and how fast? https://www.boatdesign.net/threads/what-is-worlds-biggest-planning-hull-boat-and-how-fast.64476/page-6#post-898807
    For a discussion of Yamato-1 see this thread.
    Anyone played around with a magnetohydrodynamic drive? https://www.boatdesign.net/threads/anyone-played-around-with-a-magnetohydrodynamic-drive.44464/
     
  12. bajansailor
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    bajansailor Marine Surveyor

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  13. comfisherman
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    comfisherman Senior Member

    I own 2x traktors. Actually helped prep a brand new one for install last Thursday on a friend's rig that's akin to one of mine. They are much improved from what they were 20 years ago (my now spare skiff uses an old style version). I've a very specific use, shallow draft around nets and even then they are a pain to live with long term. Probably in thebl 2025 rotation I'll build a conventional skiff with shaft and a likely nozzle for 75% of the season. Leave the jets for the high value high intensity uses, when logging the big hrs they aren't up to the same level as big slow turning wheels.
     
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  14. SET Project
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    SET Project Junior Member

    @jehardiman Thank you for the explanation. I had not heard about the square cube law, but it is an interesting relationship between volume and area. Waterjets are still very young and have much room to progress. But it seems as though its natural limits will be to small sized and high performant vessels. (I'll take a look the discussions)

    @bajansailor I'll take a look at TraktorJet systems. Thank you
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    Quite the opposite.
    Waterjets are fully mature and have been for many years - they are the industry standard for high-speed vessel.. Perhaps you have not used them or know much about them.
     
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