Catamarans High Speed Blow Over - Causes & Solutions

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

  1. groper
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    groper Senior Member

    At which point the vessel needs full self stabilizing aerodynamic properties - something which all these boats dont seem to have... why is that?
     
  2. DCockey
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    DCockey Senior Member

    CG is too far rearward. They would probably be stable flying stern first.
     
  3. kidturbo
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    kidturbo Junior Member

    I think that's pretty much laid out above.. First came the race catamarans, then came a guy who wanted one to haul his 4 buddies along on Saturday. Now ya got race design hulls, modified for "street use".. His buddies liked the ride, so they ordered one too, and here we are. :rolleyes:

    Thanks again everyone for sharing some great knowledge on why these boats fly across the water so nicely, and in the air so badly. Overall if you counted up the usage hours, compared to the amount of accidents, it's gotta be pretty favorable statics. But tell this to an Insurance company who use the standard 50mph V-bottom as their performance baseline.

    After reading jimboats article on "what makes a tunnel hull work" I'd rank these high powered boats with the same operator skill requirements as RC aircraft. About anyone can be taught to fly one successfully, the key being taught..

    When I decided to learn RC helicopters years ago, I dove right in to a mid sized 3D performance nitro powered craft. A little reading and watching a few videos proved to be utterly useless teaching tools. After some costly crashes I stepped back down in size to something smaller and easier to learn with. Between that and some cheap flight simulator software, I soon picked it up enough to a point I can now enjoy flying.

    Maybe that's a feasible approach to this problem, a nice flight simulator program for prospective owners. Something with the ability to teach setups on all the popular boats, and create departure situations that one might encounter. They use these to teach river boat pilots, why not pleasure-craft?

    On the other side of this needs to come advancements to the craft itself. Even the worlds best RC heli pilots will tell you it was almost impossible to fly one before the introduction of the head-holding gyro. This little device keeps the nose pointed where you last left it, no matter what changes you make to the collective pitch or throttle. Now they make 3-axis gyro models with added collective control, allowing a novice to hover like a seasoned veteran in minutes.

    That's how I see this being solved. More extensive training options plus some new technology. Teach the operators better how these boats can react when least expected, and how to respond, or better yet avoid such situations. Then add some modern technology to handle the unknowns that pop up way too fast for human reaction. Be it horizontal stabilizers, canards, or even fast opening deck panels acting as spoilers, computer aided these could be the anti-lock brakes for a boat. So many options, the technology available, and nothing implemented. I understand the sentiment.

    But it's not for lack of innovative thinking. From Jimboat's article listed above.

    Ballast tanks have been used to change the CG by as much as two or three feet - all on the command of the pilot, and in less than a second. We have even seen the use of 'water-brakes' that can be actuated to create phenomenal drag at the extreme trailing edge of the running surfaces (causing an overpowering positive moment about the CG) to make a 'last-ditch' correction for a suddenly increasing lift component

    So I'm all for presenting options to the masses, and letting the market decide. For one, the 38' cat project parked in my front yard will probably get the best active aerodynamics solution we can come up with from this discussion. Betting a few others I know would be open to testing an aero or hydro based solution also.

    ;)
     
  4. BMcF
    Joined: Mar 2007
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    BMcF Senior Member

    Active computer-controlled ride and flight control has been around for quite a while for a range of high speed vessel designs, including hydrofoils. Adding aerodynamic devices to those systems would not present any technical control hurdles except for the selection of the appropriate devices and their integration with the vessel.
     
  5. powerabout
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    powerabout Senior Member

    The designers dont understand the forces clearly, there was another 2 guys killed in the UAE and the onboard video captured it, ugly, but if you turn it over then you would think the deck needs to be as strong as the hull as you are about to impact the water with the same speed?
    In this case the deck outside of the cockpit collapsed and blew the bulkhead behind the drivers into the dash. It was going backwards. Lots of panic in the class and all boats upgraded but it happened again.
     
  6. powerabout
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    powerabout Senior Member

    because the drive is from the water and has significant control over the longitudinal lift ( as long as its still in the water)
    What does a tunnel boat drive do when the bow goes up...
    nail the throttle as the props are all transom lifters
     
  7. kidturbo
    Joined: Sep 2013
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    kidturbo Junior Member

    From a purely aerodynamic standpoint, is it possible to create much down force or spoil the airflow going under the boat using a "Slat" type device on the leading edge of the wing/tunnel? I understand slats are typically used to increase lift and lower stall speed by changing angle of attack, but what if you flipped this design?

    SlatInstalled_side_view.jpg

    Just thinking of solutions that wouldn't increase drag while retracted, but could be actuated quickly if bow angle increases beyond a set value.
     
  8. kidturbo
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    kidturbo Junior Member

    Statement Venturi Tunnel

    Saw one of theses up close last week, strange looking bow. I see they claim to have solved the blow over problem, and patented it. Only time will tell I guess.

    [​IMG]

    From http://www.statementmarine.com/models/50-passion

    Patented Custom-Tuned Venturi Tunnel

    Cat 101: As a cat flies across the water, air is packed into its tunnel, creating a pressure wave that lifts the hull. The faster a cat goes, the more lift it creates. This lift gives cats their speed, but too much lift can result in a loss of stability, or, in extreme cases, even cause the boat to blow over. At high speeds, drivers will fight a cat’s natural tendency to fly, by using drive trim to reduce lift and maintain control. This battle – lift vs. balance – is at the very core of high-speed cat operation.

    Statement has solved this “cat conundrum” by creating the Custom-Tuned Venturi Tunnel, a patented design incorporating molded “tubes” to increase tunnel width and dramatically enhance airflow. The entire surface of the tunnel – sides as well as ceiling – have been specially tuned and tapered to focus the pressure right at the boat’s center of gravity. The result is an unprecedented level of high-speed balance and stability. In factory tests with professional drivers, the 50 Passion attained speeds of 180 mph, with no use of trim.

    :?:
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    Beats me how the centre of air pressure would remain constant regardless of pitch angle.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    .........and come to think of it, if it really did, what is going to stop the rotation ?
     
  11. kidturbo
    Joined: Sep 2013
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    kidturbo Junior Member

    That boat looks very stable in the video on smooth water. They're always out front on cool innovations, like the air ride cockpit . But that bow looks just as strange in the water as out.

    [​IMG]

    Wonder how the hot tub figures into the COG point?
     
    Last edited: Sep 15, 2013
  12. DCockey
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    DCockey Senior Member

    Assuming the aerodynamic devices can generate sufficient forces and moments at the needed locations with quick enough reactions, and do so without causing too large a detriment in performance or other requirements.
     
  13. El_Guero

    El_Guero Previous Member

    So, which is it?

    Safety first, or rules first?

    You can have two firsts, first place wins, and second place is the first place amongst all losers. Quoting a football coach, who evidently knew more about aerodynamics than many of your all knowing 'engineers.'

    I think I would go with the football coach and the aerodynamic engineers on this question.

    ;)

    wayne
     
  14. El_Guero

    El_Guero Previous Member

    Your real problem is not the aerodynamics.

    That is real easy for any basic engineer, has been since the barnstormers of the 1920's and 30's.

    Your real problems are at least two fold.

    One stability - the better you tune the device for stability, the more force it will take to move it out of stability, that is good and bad. Because, just like the back flips the sport is experiencing, once you are out of stability, you will slam with a lot of force.

    The other problem is the 'pilot' deciding he is 'now safe.' In this event, you would always be a split second away from a "controlled crash" landing. And the pilot MUST KNOW THAT AT ALL TIMES.

    Study the WW2 fighter aces and what they went through as they went from 'newbies' to aces. The growth of real knowledge, practical knowledge, must be a part of this sport, or you will only continue to lose a lot of fellow risk takers.

    The guys, who are alive, you need to be asking this of are the high performance air racers.

    They are a mature bunch of pilots, engineers, and backers who have weathered many fatalities, and they have worked through the pain of safety taking a back seat, safety is in the back seat every time there is a death.

    Once dynamically controlled, the boats will have HUGE ability to fly, I would think even given a little chop to the water.

    As for the gyros, gyros are stable, one of your videos seemed to imply the opposite, but they are stable. The misconception would be trying to 'turn on' a gyro only when needed. That will NOT work. It must be 100% on to give proper stabilization.

    They use them on big ships (cruisers, that is why they list so badly when they lose power), and they really use them on Navy ships, and Army tanks. Stabilization is old technology.

    It is time to forget the silly rules, and put safety up where it should be - FIRST.

    You should also design the cockpits on these to survive a +50% speed differential. When cruising at 200 mph, survive a 300 mph crash. That will involve air bags, and active restraints, 5 point would be a good start.

    And a lot of added hulls and bulkheads. EPS can absorb huge impacts. Strengthening the cockpit should be along the lines of the P38, F6F Hellcat, or P47 Thunderbolt.

    :)

    Then "put the throttle to the metal." And let's take off.
     

  15. BMcF
    Joined: Mar 2007
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    BMcF Senior Member

    I agree...but the "quick enough" part is equally fundamental to the active vessel motion control systems already out there, moving tabs, flaps and foils underwater.

    The current state of the art vessel ride control system is acquiring the motion data at 2000 hz, and processing and issuing position commands at 200 Hz, to fin, flap, tab hydraulic (or in some cases electric) servos with very fast actuation rates and short response times.

    So yes....the question remains as to what actively controlled "device" would be effective at producing the required force(s). But how to control it is the part already solved. Quite a few years ago we did look in to actively controlling some slat arrays on a WIG design.
     
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