Air injection for planing hulls

Discussion in 'Boat Design' started by CDK, Feb 3, 2008.

  1. mmd
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    mmd Senior Member

    As stated, we didn't have the money to build a trial horse. However, with previous boats built with similar hull forms in varying sizes from 28 to 60 feet LOA, the accumulated trials data was used to refine our in-house hull speed prediction program to the point where we were confident of our velocity prediction to within a knot or less. The Ocean Mist shattered those predictions with a vengance, with no other variables other than hull afterbody form (which should have created drag rather than reduce it) and air injection along the planing surface. We didn't investigate further because the client was happy and we were in the business of building boats, not doing academic research on them. I have no better proof available other than a successful build.
  2. tinhorn
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    tinhorn Senior Member

    Found this while I was searching for something else:

    Attached Files:

  3. rwatson
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    rwatson Senior Member


    Now the the other variables start surfacing!

    How simple would have been to turn the air bubbles off and record the "non aired" performance?

    Record the average speed on GPS for 10 minutes, average speed on GPS without bubbles for 10 minutes - keep that up for an hour, and you should see a healthy trend despite variance in winds.

    If I was an owner, and I had spent money on the innovation, that would be the first thing I would have done! If I was the designer it would have been top priority for me!
    Last edited: Feb 3, 2008
  4. tom28571
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    tom28571 Senior Member

    My argument exactly. Michael, I have no problem with your work. Quite the contrary as you have showed some impressive designs and always have good thoughts or advice for us amateurs and designer wanabes. Maybe it's because some guy was just trying to send $2,000,000 if I would only advance him $2500 for some expenses.
  5. rambat
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    rambat Member at large

    Ocean Mist

    MMD, How much did the Ocean Mist weigh? Also I think Tom is confusing trapped bottom bubbles with aerated or frothy water. Anything, including air-bubbles (pressurized not cavitation) which displaces water between the hull bottom and the surrounding fluid will raise the hull equal to its own displacement. If that was not true a hovercraft would create a very deep hole in the water in defiance of physics.
  6. mmd
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    mmd Senior Member

    Ocean Mist's air-induction system was not pressurized nor one that could be "turned off". It was an atmospheric system, controlled slightly by a damper in the ventilation duct, that relied on a pressure differential of the water flow along the hull (cavitation in the sub-transom) to draw air into the slipstream. And, yes, we did do a series of trials at varying amounts of damping of the air ingress and at varying speeds and sea states.

    C'mon, guys, think about what you are asking... Do you really think that I built a large, expensive boat with a novel hull feature and did not do as complete a program of evaluation trials as I was able to? They were not as controlled nor as exhaustive as I would have liked due to time constraints and client demands, so I didn't publish a technical paper on the hull, but I didn't just build it and send it on it's way. I do have a pretty extensive amount of data on the performance of the hull; enough to convince me of the efficacy of the concept within certain limitations. Enough, also, to convince me to not make every detail public, either. <wink, smile> To paraphrase my esteemed colleague and fellow forumite John Hardiman's byline, "The only thing a naval architect has of value is his data base", and that is not to be given away freely.

    Her full-load displacement was approximately 18 long tons.
  7. BMcF
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    BMcF Senior Member

    Positively ventilated steps in planning hulls have been successfully implemented on many craft. The Russians were heavily in to 'air lubrication', even for non-planing hull types. We have worked with several designs over the last 20 or so years, and the results for the air-lubricated non-planing or semi-planing vessels were routinely diappointing. But the benefits for a planing monohull have been proven.

    There is (or used to be) a monohull crew boat working out of Jacksonville, Fl that was retrofitted with a ventilated step and the blowers to force air through it. With no change in the powering (DDA 12-71s IIRC), the top speed was increased from roughly 28 knots to 34-35 knots. Unfortunately, I cannot lay hands on my notes about what the air-HP requirement was...I do recall that there was a common 'plenum' built over the step and used roots blowers bolted to it, end to end, to provide the air.
  8. Village_Idiot
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    Village_Idiot Senior Member

    I mentioned this in another thread a while back, but here goes again.

    Back around 1993, the science journal Nature had an article on hydrodynamic flow. The researchers were testing the speed of water through a pipe or sluice and found that random projections on the inner surface of the pipe increased the water velocity something on the order of 15%. Uniform projections increased water velocity minimally, perhaps insignificantly. They summarized that the real key was that the projections had to be random.

    The theory behind the projections was that with a smooth surface, water flowing next to the surface was slowed down by friction against the surface. This slower-moving water would tend to "roll up" much like you would roll up a rug, and create large vortices. Once the vortices became large enough, they would break away from the surface and into the more mainstream water flow. The "breaking away" action is what caused turbulence and slowed overall water velocity. By adding the protrusions on the surface, the vortices were broken up before they got very large, thus improving overall laminar flow adjacent to the surface.

    Take-home message: For hull design, you won't get laminar flow right at the surface, no matter how slick. The trick is in controlling laminar flow just a few mm away from the surface to enhance overall flow. Random protrusions seem to be a good start at doing this.
  9. TollyWally
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    TollyWally Senior Member

    "Take-home message: For hull design, you won't get laminar flow right at the surface, no matter how slick. The trick is in controlling laminar flow just a few mm away from the surface to enhance overall flow. Random protrusions seem to be a good start at doing this."

    Is this similar to the sharkskin "rougher is faster" idea?
  10. Fanie
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    Fanie Fanie

    I haven't read all the posts in detail. The simplest way of 'air' injection would probably be achieved using the hull. My power boat has a semi cathedral hull. At low speed the outer hulshapes pushes the water towards the centre hull, so it gets on the plane faster and easier. I'm sure air forced under the hull does make some difference, but considering the boat's weight and the inefficient shape for tunneling air under the hull this would have a neglectable difference.

    If you want to add air into the water / hull part you either have to go much faster than what I can go, or have something that induces air into the water (bubbles) just before the planing area. Keep in mind that this creates another set of problems, props like solid bubble-less water to bite in, otherwise the prop starts to cavitate and you lose more than you gain.

    Maybe a wabble front in the hull planing area could cause water surface disturbances, as long as the drag it creates is less than the gained less friction.

    If you're looking for pushing air between the hull and the water surface, I guess you're looking for a hovercraft... ?

    If you're after more speed, just maybe one could pay better attention to the planing area shape of a hull - there may be something there yet, but I'm no expert on that. Something like a twin shallow hydrofoil as mentioned somewhere previous that would take over the planing area at a certain speed.
  11. tom28571
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    tom28571 Senior Member

    I don't think so, but there is obviously a lot more to be learned here than can be taught by a simple yes or no answer. I think hovercraft are supported by two forces and neither is air bubbles. Unless the air under the skirt of a hovercraft is equal to or less than(not) the pressure outside the skirt, there must exist a hole in the water. Not enough to support the craft, but some. This is off-topic anyway.
  12. AmnonMikeCohen
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    AmnonMikeCohen Inventor

    There is already LOTS of work in this art

    As to marine application of the idea, there are many marine vessels already using this idea, and if you search Google Images for Surface Effect you should see much of what is already there.

    The WIG (Wind In Ground) Effect, is actually applicable to Seaplanes and not to Boats and Ships - as it is in our focused interests!

    The best I have found, which has less problem in open seas - of the air leaking out from under the hulls, is The Norwegian Skjold Surface Effect watercraft.

    There is a lot to gain by employing the concept, but only my invention goes where no one has yet been able to develop, but it is still useless for you and our readers, as I am keeping it as a highly valued trade-secret and am only working on the water-lubrication layer part of my multi-lubrication surface effects hulls; an advantage which can be added to all existing hulls already.

    The tests show 30% increase efficiency by air injection, and there are other lubricants' options developed which are economic for use - but the extra power for air-injection is needed and must be added plus installed on a boat or ship to be effective.
    It is a good idea, and is in use, but the USA Navy has not yet mastered the capabilities in a way which is very economically beneficial, while ignoring my development because I am not willing to be dishonest with the USA taxpayers who subsidized my scholarship education, many years ago, and which is why I want the benefit to be honestly in the best interests of the American people.

    :idea: Here is where you may find, the American model of the invention, published in 1996 It unfortunately has The Leaking Air problem...

    Please do not hesitate to ask for more information, here or directly, from developers and owners of this knowhow.
  13. CDK
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    CDK retired engineer

    mmd's "Ocean Mist" gained 20% speed with just a clever hull design to introduce air in the boundary layer. No blowers, ducts, valves or plenum that might be considered as negative factors for reliability. Yet it didn't start a hull design revolution.
    I bet that if a passenger car manufacturer found a simple way to improve fuel efficiency by 20% the whole industry would follow immediately. History shows that even a not so simple improvement like overhead cams, 4 valves per cylinder and common rail injection was rapidly accepted and became general practice. Felix Wankel's rotary engine was an exception, but that had to do with patent rights and the making the whole existing engine industry obsolete.

    Why there is so much conservatism in the boating industry I can only guess. Maybe because the disciplines of hull design and propulsion each follow their own path or because the volumes simply aren't large enough. And it is of course much simpler to install a larger engine when more speed is required.

    rwatson's suggestion to do a scale model experiment is tempting, but it would be tough to measure differences in speed, find a pond without waves etc. And you all would not be impressed if I would report that my air injected toy boat ran 15 minutes on a battery charge instead of 10.
    But there are some derelict fishing boats nearby and I happen to have a garden blower I never use because it is so noisy.....

    Village_Idiot, the information about random projections is not correct. A hull with a lot of barnacles is slower than a clean, waxed one.
    I once shortly worked in Martonair's laboratory where I developed an empirical formula to predict the flow capacity of compressed air through a tube, based on pressure, tube length and diameter. Any obstacle that causes turbulence reduces the output, even fittings that did not reduce the diameter but had a gap between tube ends.
    It was a pneumatics company, so they were not interested in liquids.
  14. AmnonMikeCohen
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    AmnonMikeCohen Inventor

    Did you look for the M SHIP design

    You are right, Fanie:
    If you look for the MSHIP design, you will see information supporting and explaining what you already have and what they are doing in this Marine Art.
    See it @


  15. kach22i
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    kach22i Architect

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