Air ventilated planing hull design

Discussion in 'Boat Design' started by Kraftzion, Jun 11, 2011.

  1. Kraftzion
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    Kraftzion Junior Member

    I was thinking that a hollow louvered tube should work for introducing air under the hull of a high speed planing boat. I'll use a fountain boat as an example. They Have a rail/pad that runs down the center of the boat. If you replaced that pad with a hollow louvered tube open at the front(above the water line) and back I would think it would pull air out of the tube thru the louvers at speed. The tube would be full of water at rest making the boat more stable at rest. When you start to accelerate the water starts to flow out the back of the tube and air in the front. You would have some water flowing back into the louvers or maybe slots is a better word. With longer more steeply pitched towards the rear slots this could be kept to a minimum. The tube would continue to clear as you gain speed until it is completely clear at which point the water running across the bottom of the running pad shaped tube would start to draw
    air from within the tube out the slots lubricating the hull. You might have some prop bite problems to address maybe a larger surface piercing prop. The front tube vent could be run up the center line of the boat in a triangular tube or run thru the hull to above the water line. or you could run a smaller tube down the transom and into the larger tube if wanted to. Is this a sound idea or am I misguesstimating the forces at work here?
     
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  2. tom28571
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    tom28571 Senior Member

    One issue I see is that the boat plunging in rough water would alternately dip the intake under, causing surge problems. Having the ram intake up on deck or at the sheer might solve that and I think it has been done.
     
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  3. gonzo
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    gonzo Senior Member

    It would ventilate the propeller. Air doesn't lubricate, but can be used to either modify flow (turbulence) and there are some claims of lessened skin resistance.
     
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  4. Kraftzion
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    Kraftzion Junior Member

    The front tube would be above the water line, main use is to break the vacuum on take off, once boat is on plane it should get air from the front and the back. If it's been done did it work? Lubricate, lessen skin resistance, create a boundary layer with less drag, whatever you want to call it. If the prop is surface piercing it is ventilated already.
     
  5. messabout
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    messabout Senior Member

    Yes it has been done and no it did not work very well. If I remember rightly, there was a boat manufacturer in the Bradenton area, circa 1958 or so, their name might have been Thunderbird Boats. They spent a bundle of time and money making ventilated runabouts. The air intake was in the forward deck and the whole thing was well done and kind of sexy looking. Despite the effort of the builder, the concept was a commercial and practical failure. Conventional hull forms of the day worked as well or better than the ventilated ones. One of the problems was that the boat was somewhat slower than a conventional hull with equal power. Quirky cavitation was another.
     
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  6. Kraftzion
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    Kraftzion Junior Member

    Thunderbird boats started in Hialeah in 1966, and the design would have to use
    a surface piercing prop. Properly designed your only aerating 1/2 inch of water, run a 1/2 inch bigger prop and your propulsion problem should be over. Here is a great video of a modern outboard prop running in surface piercing mode.

    http://www.youtube.com/watch?v=PZm11iP0EUU
     
  7. gonzo
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    gonzo Senior Member

    Technology either works or it doesn't. However attached you are to your idea, I see more problems than advantages. RIBs use tanks that are full of water at rest and empty at planing speeds. Designing a hull that uses aereation that will not interfere with the propeller in all conditions may be possible. It would not be with air coming from the center as you describe though. Also, surface piercing props are designed to be ventilated as they exit. If you also ventilate them randomly, the performance will suffer.
     
  8. Kraftzion
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    Kraftzion Junior Member

    I really think the prop is a non issue. A deep v with twins like most Fountains, the motors are not even inline with the pad. A Arneson is far enough out back that it shouldn't matter. I am more interested in the interaction of the plate and water, how fast before the water pressure is overcome and the surface speed starts to draw air out between the plate and the water. Pretty much all race boats are ventilated any more, its just done in a different way- steps which break the boat loose among other things. It has already been proven by people smarter than me that a boat will run faster on a layer of air than direct water to skin interaction. Our military even uses the principal to make their torpedoes faster. This just seems like a simple way to do it, I thought one of the engineers on here might be able to tell me why it would/wouldn't work.
     
  9. gonzo
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    gonzo Senior Member

    We keep on telling you why it won't work. Your responses are, for example: "the prop is a non issue". You also confuse a ventilated hull with a stepped hull. Unless you study a bit more physics and engineering, the answers won't make sense.
     
  10. Kraftzion
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    Kraftzion Junior Member

    apparently you are not even bothering to read my posts, already gave you the reasons why the props are a non issue. Nothing you have wrote has addressed the physics or engineering involved. forget it.
     
  11. BMcF
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    BMcF Senior Member

    I've seen a couple examples of successfully applying forced-air lubrication to planing monohulls of about 22m LOA. Both were 'crew' boats that operated in the high 20-knot spead range. A ventilation 'step' was created along the guesstimated forward boundary of the planing surface of the hull and that step fed with air from a bunch of old GM diesel roots blowers operating in parallel, end to end to end, mounted on a crude plenum built over the step. I do not recall how many or even specifically what size those blowers were (4-71, 6-71, etc).

    For all that extra 'stuff', the boats gained a frankly amazing 5-6 knots of speed compared to the original configuration. The owner/operator competed for 'crew taxi services' to MSC vessels anchored off shore and the extra speed was a benny for winning the contracts he needed.

    That one example excepting, I've seen failure after failure of other air-lubrication schemes over the years, the most numerous and notable being, for some odd reason, always catmarans.

    Note alos, whether a technical success or not so much..the air in all these attempts at air lubdication is forced via some kind of blower.
     
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  12. yipster
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    yipster designer

  13. Kraftzion
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    Kraftzion Junior Member

    Thanks!

    BMcf , I haven't seen your post until now, thanks for the positive input. Yipster you made my day- I thought it might work if properly designed.
     
  14. Kraftzion
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    Kraftzion Junior Member

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  15. tom28571
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    tom28571 Senior Member

    That is nothing but a sales video with no meat. THere are some tests on boattest.com.

    I wonder what they have that is patented since everything I can see has already been in use for a long time and the captured air along the chines is already patented. Ram air vents from above the water have been in the literature for over 50 years, at least. Usually such patents cover only some obscure part of the design so they can say "it's patented".
     
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