A ground effect boat. Not the first and certainly not the last

Discussion in 'Boat Design' started by schakel, Sep 26, 2022.

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  1. schakel
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    schakel environmental project Msc

    Last edited: Sep 27, 2022
  2. clmanges
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    clmanges Senior Member

    That was my first thought. I can't help noticing how so many of these promotional videos are made in ideal conditions. They should show us what it can do when things get ugly. I relies on speed to attain fuel efficiency; how does it stack up against other kinds of boats when sea conditions don't permit that speed?
     
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  3. jehardiman
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    jehardiman Senior Member

    Yeah, and also notice that there are no other wakes. Around the 1:45 mark in the video is the only time it is more than DFC, and she is hull walking. I think her performance "advantage' (in DFC water) over other 100 kph (53 knot) vessels is windage drag; however the fully enclosed structure has significant mooring, maneuvering, and operational issues. I would be surprised if there is any significant WIG effect above SS 1-2. Finally, there are no passenger seatbelts; a "crash and burn" at 50 knots would throw everyone into that big viewport.
     
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  4. mitchgrunes
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    mitchgrunes Senior Member

    1. I think nearly all aircraft use the ground effect during take off and landing.

    Based on a quick web search:

    2. Many web pages outline safety hazards associated with GEVs (ground effect vehicles). Some websites also claim that high altitude aircraft have lower drag than GEVs.

    3. I wonder if there are FAA rules on GEVs, and whether you need a pilot's license.

    4. Are there reasonably safe low speed GEVs other than hovercraft built for recreational boating in calm fair weather conditions? I picture something small and inflatable, that you stow in a trailer or vehicle when not in use.

    5. Some hang gliding enthusiasts do "ground effect gliding". But hang gliding has always been dangerous.

    6. Some birds (e.g., pelicans) fly very close to the water under some conditions.

    7. There are websites on making your own paper airplane style GEVs.

    8. Even without looking, I'm sure there are ground effect drones for civilian, military and reconnaissance use.
     
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  5. philSweet
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    philSweet Senior Member

    Incase this grows legs, here's a decent primer. Mostly because it is very explicit in describing and isolating two separate mechanisms that alter the performance of wings in ground effect. The ram effect (lift increase) available to this craft is very modest - certainly less than 10 pounds/sqft. Probably less than half that is realized, and it might be zero in order to manage sneezing and stability dynamics. The span effect (drag reduction) is rather difficult to assess given the low aspect ratio and the endplates.

    Wayback Machine https://web.archive.org/web/20100922210513/http://www.ptmts.org.pl/abramowski-2-07.pdf

    In particular dig through the lift pressure charts and look at where the pressures change. They change on the top surface, not on the bottom surface. These aren't air cushion vehicles at all.
     
  6. BMcF
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    BMcF Senior Member

    Nailed it. If I had $100 for every similar crackpot design I've been asked to evaluate over the last 35 years..I could buy a round for everyone. Stilleto comes quickly to mind...as a more recent example.
     
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  7. jehardiman
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    jehardiman Senior Member

    Perhaps WIG is not the proper term. The paper "Wing-in-ground effect vehicles" by Kirill V. Rozhdestvensky (Progress in Aerospace Sciences 42 (2006) pages 211–283) list the following interim IMO/ICAO
    guidelines:
    Rozhdestvensky does reference RW Gallington's paper "Power augmentation on ram wings" (Proceedings of the symposium ‘ram wing and ground effect craft’. London: The Royal Aeronautical Society; 19 May 1987) as using the term "Ram Assisted Catamaran" (RAC). I haven't seen that paper on how that is different from a SES, most likely how the lift pressure is generated ( perhaps similar to the large soviet ekranoplans where the engine exhaust is used for under wing
    pressurization).
     
  8. philSweet
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    philSweet Senior Member

    And I think "ram wing" is very misleading unless the ram effect is generated by the propulsor as in the above documents. It's not that you can't pressurize the area below the wing in ground effect with flaps or an angle of attack, it's that it is a bad idea. You want the bottom surface of the wing to be flat and at zero angle of attack relative to the surface. Everything good that can happen has to happen on the upper surfaces. The real benefit is that the wing operates at a lower angle of attack, and that is the principle mechanism for WIG drag reduction.

    DTNSRDC ASED-396 Analysis of Empirically Determined Aerodynamic and Ram Coefficients for a Power-Augmented-Ram Wing-in-Ground Effect by David G. Rousseau. Analysis of Empirically Determined Aerodynamic and Ram Coefficients for a Power-Augmented-Ram Wing-in-Ground Effect. https://apps.dtic.mil/sti/citations/ADA049636
     
    Last edited: Sep 29, 2022
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  9. jehardiman
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    jehardiman Senior Member

    This is why "salt", not "pork" is important.
     
  10. schakel
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    schakel environmental project Msc

    Reason I asked is the groundeffect will play a lifting factor in the new AC 40's produced by McConaghy Boats.
    Two boats already operational, Alinghi and New Zealand.
    The new protocol forbiddes a hollow tunnel hull. This would make a monohull a catamaran or trimaran was one of the reasons.
    AC 40 bottom.png
     
  11. S V
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    S V Junior Member

    Newbie question: hull walking of that catamaran in this video = chine walking?
     
  12. jehardiman
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    jehardiman Senior Member

    Pretty much; it is a oscillation caused by a regular periodic imbalance across the lifting surface coupled with a small roll inertia or large roll moment. Fairly common on high speed racing cats (sail or power) or 3-point hydroplanes. It starts with a wave profile difference or wave crest stagger across the lifting surface and then can be self amplifying until a speed/course change or a "major dynamic event" occurs.
     
  13. S V
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    S V Junior Member

    Thanks, Jehardiman,

    I kinda like the idea of this boat. Could you elaborate for my uneducated mind what are the reasons for this behavior in this exact boat? Is it related to the fact, that CG is very high AND demihulls are very far appart? In layman terms - if I have to quick fix this boat, retaining its idea, how can i do it?
     
  14. jehardiman
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    jehardiman Senior Member

    If you have a "quick fix" .. you haven't thought it through. Not my place to give it to you to kill someone else.
     

  15. S V
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    S V Junior Member

    Yes, safety should always be first and my idea to fix unfixable perhaps is too radical... I fully understand that there is no quick solution to all the problems mentioned in this thread, but lets say if I want pretty high speed 30-35+ knots similar displacement catamaran with similar deadweight and do not want it to have hull walking - what are the things to do and dont?
     
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