Catamarans High Speed Blow Over - Causes & Solutions

Discussion in 'Hydrodynamics and Aerodynamics' started by kidturbo, Sep 11, 2013.

  1. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Those bumps are known as "tubercules" and they are evident on the fins of
    some whales and other aquatic mammals.

    Kristy Hansen at the Uni of Adelaide recently completed a PhD on these
    types of wing modifications. Her thesis and papers will have an extensive
    collection of references to start you off: See:
    http://www.adelaide.edu.au/directory/kristy.hansen
     
  2. kidturbo
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    kidturbo Junior Member

    Thanks for the link, I've started reading hers and some others work on this. When searching, "vortex generators" returns the most relevant images of applications. Which there is plenty of related material demonstrating flow characteristics on many surfaces.

    Most common automotive usage is on the roof surface to energize the stale air over the rear deck, proven to reduce drag or improve a raised deck wing performance.

    [​IMG]

    A side installation to reduce drag.

    [​IMG]

    --

    One nice thing I see about theses, they are available pre-fab in many shapes and sizes. So they can easily be installed, tested, moved or removed without messing up a surface. That's a huge plus when talking about speed mods on a performance boat, cause no one wants mess up a paint job for experimentation.

    Could they stop a blow over? Probably not alone. But as Petros mentioned they could be strategically placed to reduce the risk of wing stall, or combined with other control surfaces. Probably improve overall areo performance on older hull designs at least..
     
  3. Petros
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    Petros Senior Member

    keep in mind that vortex lift, and/or using vortex generators, has a "cost". It does increase drag. they can be used to reduce drag to keep the after body flow attached if you have LESS THAN AN IDEAL shape, so they are an effective band-aid when an ideal shape is not practical. The other place they are useful is when you need to keep the flow attached to prevent stall when at angles where flow would otherwise want to separate.

    On a tunnel hull speed boat with a canard, you have to have the canard an integral part of the design to maintain level "flight" in grond effects, and than if you increase angle of attack and climb out of ground effects, it needs to lose lift so it brings the nose back down.

    An alternative is to keep lift at the aft end of the hull, and increase it at high angles of attack. If straks or vortex generators are used to increase aft lift when at high angles of attack, it could serve to bring the nose back down (more lift in the back you get a nose down pitching moment). These vortex generators will increase drag, both when active, and when at low angles of attack when you do not need the extra lift.

    So the design challenge with either is to minimize weight and drag when in the normal configuration of operating within the ground effects. when out of ground effect, at a high angle of attack recovery mode, the drag is not so much a concern since you are just trying to keep the hull within a controlled "flight" envelope.

    the used of strakes or vortex generators is a possible solution, if applied carefully.

    Strakes work in a similar way as a row of vortex generators, but look very different. I would tend to favor the strakes since their appearance can be made to look stylish as some kind of "rocket fins" on the aft part of the hull, in essence fooling the uninformed as to their purpose as an essential aerodynamic safety feature, but rather looking like retro classic styling from the 60's.
     
  4. powerabout
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    powerabout Senior Member

    I can see a big canard fore and aft connected to a flight control computer
    Will cost more then the boat
     
  5. kidturbo
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    kidturbo Junior Member

    All the boat videos I've offered up as examples of blow overs were running a pair of engines that cost well over $250,000 US. Brand new Mercury Racing 1150hp engines START at $120,000 US each. That's not including the $50,000 plus #6 or #8 dry sump drives they are powering. Then add a modern composite fiber hull, paint, some top shelf electronics, and set it all on a nice 100k tilt trailer. Forgot we also need a matching truck to tow it...

    So when I compare these boats and technology to that of an Enzo or Bugatti, there is a good reasons. I'd say our budget for computer aided flight controls should be pretty high. But not necessarily the case, modern control systems are actually pretty cheap.

    --

    Where I have found an interesting use of canards in marine sports is river racing jet boats. These are typically a 24ft aluminum hull with a racing engine hooked to a jet pump. Lately they've also started running turbines like the T-58 making 1300hp or more. Being so short, with the CG far aft, they use an adjustable canard to "fly" the bow with great success.

    From one of these boat racers web page. Mark Cromie

    "The way it’s set up at the moment with the 1350hp turbine we can run 120mph with the front canard wings on. The wings are adjustable from the steering wheel and we either run neutral or lifting wings, that can adjust the down force on the front of the boat to suit the conditions."

    Here is another video, from one of these extreme jet boat racers for review.

     
  6. rxcomposite
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    rxcomposite Senior Member

    Canards are used as control surfaces in this case. No lift benefits.

    The biggest problem is the prop thrust line. It is below the VCG and will always try to lift the bow up (like the motorcycle trying to do a wheelie). Locating a wing near the CG will cure it but only at speed when lift is generated. So there is still this dynamic CG that you have to chase/keep within control.
     
  7. kidturbo
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    kidturbo Junior Member

    Thinking that's something these large tunnel boats could benefit from, a small canard providing zero lift acting only as a control surface?

    Example, a computer based flight control system that becomes active above a set speed. Once it reaches say 80mph, the system activates and the canard moves from it's locked neutral position to become an active control surface. It's only job is to maintain bow AOA within the designer specs. Small cockpit trim adjustment could be allowed, within a set degree of those specs. But basically it only job is to sense the bow lifting [or diving] and correct it.

    That prop thrust line is currently the only angle control you have. However the speeds at which it can be changed are not near fast enough to recover from a "jump" in AOA. Like RX said, it's always lifting on the bow by design.

    So from all these great posts here is what I've narrowed down as some options.

    1) Actively controlling the bow angle of attack with surfaces to avoid excessive lift conditions.
    2) Lifting the stern up to compensate for excessive bow lift.
    3) Changing drag forces when airborne to overcome excessive lift and high AOA.
    4) Dumping the lifting air from the tunnel area.
    5) Employ devices that improve stall speed and allow higher AOA before stalling.
    6) Deploy COG changing options such as fast acting ballast tanks to compensate bow lifting.

    Did I miss anything?
     
  8. kidturbo
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    kidturbo Junior Member

    Blow Over Claims Another Life

    Less than a year from where we left off, another fatal crash.



    This time it's a well known designer and industry leader "Mike Fiore" who paid the ultimate price. So sad that this continues to happen.

    This crash was caught by multiple still photographers, so besides the video there is a collection of data and photo angles to examine. By far the most of any blow over event, so please review these.

    See: http://lakeexpo.com/lake_events/out...ion_17a56d0a-2b2e-11e4-83ad-0019bb2963f4.html

    Updates on research:
    I have received pledged support from a major player in the cat racing world to help solve this quickly. Have what I feel is a feasible solution based off common existing technology and the contributions listed here that should fit any boat. Currently securing the wind tunnel time to scale test, but need some true scale models of existing hulls. Also been working to build the trigger system that includes GPS, 3-axis gyro, and AOA inputs.

    Anyone interested working on this first hand going forward please let me know. The goal for short term is trigger parameters and related hardware. Things like active aero are still on the table, but for now my testing is focused on creating drag and the KISS principle...

    -K
     
  9. powerabout
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    powerabout Senior Member

    the boats will keep blowing over, they accidents just need to be survivable.
    When there is structural failure that fix should be pretty simple..
     
    Jimboat likes this.
  10. kidturbo
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    kidturbo Junior Member

    Can't disagree that there was a degree of structural failure relating to the canopy. Stronger / reinforced steel cage structure "may" have alleviated some of that. But this was a worse case landing. 10k lbs at 180mph from a height of over 60 feet, when ya do the math?? However, both occupants survived the crash this time. Sadly Mike died from complications relating to surgery days after the fact.

    Never the less, our topic here is "cause and solutions." I felt this event best demonstrates one of the factors we had previously discussed on cause. This was a standing mile acceleration event. He was trimming for maximum speed when the departure occurred near the finish line. Calm water, with no outside interference to disrupt air flow that we can tell by sight alone.

    Purely angle of attack related event that could of "IMO" been sensed and counteracted by electronic measures reacting faster than driver trim adjustments.. Either active aero features, or simply deploying excessive drag to stern (IE a chute) may have halted it. Sound feasible?

    Below is another video with a better viewing angle. From the finish line you can clearly see it starting to go critical AOA at about 1.5-2 seconds before complete departure. As fellow engineers, what's your thought on the pressure changes above and below the foil? Totally measurable under AOA principles correct?

    https://www.youtube.com/watch?feature=player_detailpage&v=B3RVc3idlSg



    Back to our wind tunnel testing requirements. Who builds the most accurate scale RC or display models when it comes to this style boat? Looking for 3 separate manufacture models to start with.

    Thanks

    -K
     
  11. BMcF
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    BMcF Senior Member

    We ( the collective "we" that build what controls advanced hydrofoils, surface effect ships, etc...borrowing, as we surely have, from the aircraft flight control realm), have been doing exactly what you postulated....for decades now. :(

    The ability of sensors to react through high performance servos that control flight control surfaces is orders of magnitude beyond what a human can do. Were it not so...fully flying hydrofoils would never have existed, but neither would any of the modern fighters either.
     
  12. kidturbo
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    kidturbo Junior Member

    Thanks for that conformation.

    Biggest problem with the HP boat industry right now is that like most, production units follow what's learned from racing. The racing rules say "no active aero" and thus you don't see technology being used to it's fullest extent by anyone. That needs to change from bottom up I guess, or from a safety aspect.

    Can you recommend any companies who are developing flight control systems that could be of use here? For now I'm looking to equip a few boat for data logging, build baseline parameters. Can contract it out, but why reinvent the wheel if I can buy one.

    Basically need GPS speed, axis angles, and incorporate the AOA data. Looking for small profile, since any smart phone will give ya the first two. Would like a stand alone box about the size of a pack of smokes that can be easily mounted on or below deck with a pressure probe pair for AOA.

    -K
     

  13. BMcF
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    BMcF Senior Member

    We've instrumented many a craft (including a lot of unmanned free-running and towed scale model) but have not packaged the entire DAS in to one small package like you suggested.

    That said..it would indeed be easy. The current "crop" of MEMS-based gyro-chips is nothing short of remarkable, with accelerations, rates, angles and even GPS in one integrated package that isn't half the size of a pack of cigarettes. We use those as the "guts" of the motion-reference-units that are part of of our ship stabilization and flight control systems.

    As for "off the shelf" systems (end-to-end stabilization kit) the only ones we've built that were compact and light enough for very small vessels (6m-15m is "very small" in our business) were "one offs" and the craft always either models or technology demonstrators (almost all for military naval applications too).


    I've personally followed the "blow-over" subject with great interest over the years, in no small part because I've always known how to implement an active "prevention" solution. Whether on ever will be deployed....time will tell, of course. And, frankly, I'm not going to volunteer to test one. ;)
     
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