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

    It is possible, but requires vast deviation from the current tunnel boats... wing in ground effect theory already has it mastered, many years ago in fact. The flight is self stabilizing and hands free... it is aeronautical design however, not boat design...[​IMG]
     
  2. powerabout
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    powerabout Senior Member

    the key is the driving force is not in the water
     
  3. daiquiri
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    daiquiri Engineering and Design

    Apparently, there is a lots of conviction here that the design of racing powerboats is a discipline in which designers work in isolation from the rest of the world, and have no insight into research in the field of WIGs and aircraft stability. It is not so.

    Every designer of raceboats has the safety of the crew in the upper zone of his list of priorities, and he will do whatever is necessary to ensure the safety with a minimum impact on the overall boat performance.

    Various flaps, fins, canards etc. (either movable or non-movable) are not a new thing and there is nothing revolutionary in them. When it is possible to use them, they are being used, as have been for decades. Examples (some boats in the pics are back from 70's-80's):

    [​IMG]
    [​IMG]
    [​IMG]


    If these devices are not used on a particular design, it is likely that this choice was determined by the racing rules, and not by designer's ignorance.
    For example, the chapter "General Requirements – All Classes" of the APBA racing rules for offshore cats (http://www.offshoresuperseries.com/CMS/files/cms_files/Forms/2011/APBARules2011.pdf - page 64) explicitely prohibits aerodynamic devices:
    25. Aero-dynamic Devices (such as wings or moveable deck surfaces) – not allowed.
    This is a resulting boat:

    [​IMG]

    On the other side, the Inboard class rule of the same association (http://www.apba.org/sites/all/files/documents/012INBOARD_0.pdf) allows them, with specific limitations:
    "40.2 Canards may be used on Inboard hydroplanes, provided they are no wider than the maximum dimension of the air trap. A maximum of two canards may be used. (Example: one on the starboard and one on the port side.) These canards may be adjusted from the cockpit while the hydro is in motion. These canards must be placed in the picklefork area; that is, in the first three feet from the bow and no higher or lower than six inches from the deck line. The canards must have positive stops to limit travel in case of control system failure. The safety Inspector shall have the authority and responsibility to approve or disapprove all mechanical parts and hardware used for fastening canards. Horizontal stabilizers, airfoils, or wings may be used at the rear of inboard hydroplanes provided they are no wider than the maximum beam of the hull. These stabilizers must be bolted in a fixed position if they are greater than 24 inches above the deck line, except in GP classes. In addition to canards, deck spoilers and/or flaps may be used to control lift provided they are installed within the 24 inch deck line allowance. These flaps may be adjusted from the cockpit while the hydroplane is in motion and must have positive stops in the event of a control system failure.

    40.2.1 Adjustable angle props, shaft angle, or adjustable skid fins are strictly prohibited while boat is underway."​

    The Rules of the H1 Unlimited class (http://www.h1unlimited.com/docs/H1_2013_Rule_Book_v1.2_070113.pdf) also allow their use, through the following articles:
    "5. Movable aerodynamic control surfaces are permitted.
    (a) Such surfaces must be hinged to the primary hull structure, not placed on elevated trusses or secondary structure.
    (b) They may not extend beyond the length or beam.
    (c) Once approved by the Chief Inspector, the driver may manually actuate such surfaces. The intent of this specification is to permit the use of driver-controlled canards, flaps and the like while prohibiting the use of driver-controlled horizontal (tail) stabilizers.
    (d) Computer-controlled devices or boosted actuators are not permitted.
    (e) Motorized hydraulic assist for the front canard is permissible. System must be operated by the driver’s foot and must continue to function in the case of motor failure."​

    And this is the result:

    [​IMG]

    So, summing it up, the choice of adoption or exclusion of stabilizing devices on a particular design depends mainly on the racing rule the boat is build to comply to.

    And not because designers are incompetent, know nothing about aerodynamics or know less than "experts" who arrogantly call others uninformed and obsolete, but then ask questions like "Why is it that no one has considered the aerodynamic stability of the speed boats once they are airborne"... :rolleyes:
     
  4. powerabout
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    powerabout Senior Member

    The wing on Gancia dei Gancia at an slight vee angle was put there to stop the chine walk...lol
    sucked in everybody
    Buzzi knows how to take the piss
     
  5. daiquiri
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    daiquiri Engineering and Design

    Good one. :D

    Sounds like a brilliant solution against the chine-walk. The boat hes shown an extraordinary longevity and an impressive competitive track record, so it seems that the wing has done its job damn well... :)

    Edit:
    Just found a great article about the history of Cesa 1882: http://www.powerboatarchive.co.uk/Magazines/2000s/2008 Cesa Mono (3).pdf
     
  6. kidturbo
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    kidturbo Junior Member

    You have basically answered the first half of my question "Causes & Solutions" in record time. Nice research...

    However the side of this sport that's recently been hit the hardest by blow overs accidents, isn't bound by ANY of those organizational rules.

    [​IMG]

    For every "1" professional race boat built by any of these skilled designers / manufactures, there is probably "10" personal pleasure craft sold. In today market, the only real difference between them lies in cockpit design.

    The primary safety regulations taken by APBA over the past decade has been to inclose the cockpit. They also added auxiliary air supplies, along with a hatch in the hull bottom so safety crews can drag you out. All once you have flipped over. Has proven successful in low speed roll overs, however the first video link I posted, "Big Thunder crash in 2011" proves this is not fool proof. Both occupants died in the crash, the canopy failed, collapsed from sheer force of the impact.

    Now back to those other 10 boats of equal performance that left the factory with open cockpits.

    I once again fall back to the automotive industry, where you can buy a 200mph Corvette convertible off the show room floor without a roll cage. Wanta professionally race it, first thing they are gonna tell ya, you gotta add a roll cage. When you examine that same vehicle up close, safety advancements by the automotive industry are actually leaps ahead of the racing industry. How many air bags have you witnessed deploying in a race car?

    So for our discussion, let me suggest we toss out the rule books and approach it strictly as engineers, reviewing cause and effect. If a safety option to prevent high speed blow overs came about that didn't offer an edge or advantages in performance, then it would probably quickly be adopted by racing organizations. I know the guys who purchase the non-race versions are interested, they love their convertibles...

    Please provide more on that Gyro concept El_Guero.. I once tested a Gyro Bike some guy had invented. Mounted on a stand you could ride it at huge angles, go around in circles, safely fast as you could pedal to power the gyro. Simple design, with amazing control.

    Cheers.

    -K
     
  7. kidturbo
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    kidturbo Junior Member

    Gyroscopic Forces

    Looking at some gyro video's for ideas that could counteract bow rise forces, I stumbled onto this Dual Gyro video. What it actually demonstrates quite well is the forces imposed on a boats COG when oppositely rotating screws leave the water...



    I'll take it everyone here understands why you don't spin both cat props in the same direction, but did you realize how much stability difference that equates to when you remove the holding forces of water?

    One subject that has been brought up on another forum is "spinning in vs spinning out" prop rotation. Typically both engines - flywheels are spinning the same direction, then one prop shaft is reversed in the drive or transmission. So now you have 2 x 6000rpm x 100lb flywheels slightly rear of the boats COG spinning the same direction, and 2 x 3600rpm x 50lb props spinning oppositely of each other, sticking 2ft off the tail of whats basically became a flying wing.

    Just food for thought there.

    Here is a video example showing the gyroscopic forces that could be harnessed for stability even without the aid of modern electronics feeding control surfaces.

     
  8. Petros
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    Petros Senior Member

    So, it is the rules. Rules are always the killer of innovation.

    it will take an aerodynamic device that will deploy or become effective, when the hull becomes airborne. When aerodynamic stability is achieved (either passive or active), the boat will return to the surface/ground effects in a controllable manner, and the boat can continue its high speed ride in relative safety.
     
  9. groper
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    groper Senior Member

    If you want cause and effect, daiquiri already provided it for you here;

    Once the boat has left the water and pitched up, only a very strong aerodynamic counter force can help you...

    Daiquiri, I know race boat designs employ aero engineers, but the lack of this innovation by the pleasure boat builders, who are not bound by any rules, suggests complete ignorance or complacency- i dont see any arrognce in a comment to the contrary. This thread is about the high speed private boat market, not race boats.

    There happy to sell a 3000hp machine capable of 140+mph, no seatbelts, open cockpit, to anyone with deep enough pockets so they can show off to their friends and yet has no inherent aerodynamic stability!!! Madness... At least Darwin will sort them out...
     
  10. daiquiri
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    daiquiri Engineering and Design

    It wasn't clear from the first posts in this thread that it is about pleasure boats. The opening post mentions offshore racing and pleasure craft, and the next post shows videos from racing events. But never mind, I have had a knee-jerk reaction to one post which was a little too much personal and patronizing for my taste, and definitely too generalized. But I do realize that quite often my own posts might leave the same picture of me in the eyes of the others, so I really shouldn't be the one who can play judge here. An eye for an eye will leave everyone blind - let's follow Gandhi's wise words and carry on with the technical discussion. :)

    My personal point of view on this issue:

    I think that you Groper have summed it up pretty well in your post - the aerodynamic control mechanisms are effective only below a certain angle of attack and pitch-rotation speed. Things can happen so quickly at speeds these boats move at, that the boat would need a very large, quick-reacting and all-moving canard/elevator to ensure it's effectiveness once the blow over has started and gone beyond the point of divergence. But "large", "quick" and "all-moving" are not easy to put in the same box. Especially not if it is a racing box which needs to be as light and performant as possible.

    Off-topic:
    By the way, I just love the nonxistent word "performant". It means nothing in English, yet everyone understands it. Isn't it so cool?
    ;) :D

    On-topic again:
    Sorry if I have to repeat the obvious thing - these are not airplanes we are talking here. An airplane can recover from the stall if it is flying sufficiently high above the ground to permit the pilot to gain speed and restore the effectiveness of the control surfaces. There is no such space below these powerboats, there's only rock-hard water. No space means no time to react either, given the high boat speeds and the fraction of seconds in which the accident happens and ends. So, in my opinion, stall-recovery methods used on aircraft will be only partial solutions in this case.

    The efforts, imo, should be concentrated on the prevention, rather than on the cure. That is exactly the purpose of the movable aerodynamic surfaces, where allowed. They serve to actively keep the boat in the level flight under normal conditions, with a limited amount of pitch disturbances. They will not do much once the bow has gone upwards to the sky.

    What can be done, then? Well, I have a very precise idea about a method which could work and is technically feasible. But I wouldn't like to expose it on a public forum. Not before I have talked with someone from the industry, to see if we can make it become a reality. All I can say is - it is not an aerodynamic device because I sincerely don't believe aerodynamic devices can recover these boats from a backflip. ;)

    Cheers
     
  11. tomas
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    tomas Senior Member

    The canopy failed?
    Isn't that unusual?

    Was it custom or factory built?
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    Then it must be a hydrodynamic device ?
     
  13. daiquiri
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    daiquiri Engineering and Design

    Yes, it must be either that or something else. ;) :p

    Cheers
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    Good luck with your little secret ! It might have been better not to mention it though.....
     

  15. daiquiri
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    daiquiri Engineering and Design

    I agree and I have regretted it as soon as I published the reply. Too late now anyways. :eek::rolleyes:
     
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