Dangerous designs?

Discussion in 'Sailboats' started by usa2, Nov 18, 2005.

  1. DGreenwood
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    DGreenwood Senior Member

    D'Artois
    I know which metal you are thinking of. Unfortunately the world is not ready to accept the idea, even though it is so superior in every way.
    The Russians worked it out on their subs.
    I attended a seminar at IBEX put on by some U.S. Naval engineers concerning the topic and came away very impressed and stunned that there is so much mythology about it and there is such an aversion to it.
     
  2. SuperPiper
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    SuperPiper Men With Little Boats . .

    A bit of a clarification about the "big" hole. The VO70 rule limits the angle of cant. The ABN boats and the Australian boat have the pivot at the hull. The Farr boats put the pivot at the maximum distance allowed up inside the boat. The higher the pivot point, the further outboard the keel bulb will be at the same angle of cant. Putting the pivot inside the boat requires the sliding sphincter gate featured on the Farr boats.
     
  3. RHough
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    RHough Retro Dude

    Thanks for the information!

    That means that 3 of 4 "big hole" boats have had keel problems and none of the flush pivot boats (small hole) have had problems?

    ... looking for patterns :)
     
  4. sharpii2
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    sharpii2 Senior Member

    I can imagine other reasons for wanting the pivot point higher up other than just increasing the sine (the distance the ballast bulb ends up going toward one side as the keel cants).

    If you raise the pivot point high enough, you can get it above the water line and keep its general condition in easier sight.

    Its curious that the rule writers never anticipate such dodges as increasing the size of the triangle rather than increasing the size of the angle.

    I remember back in the days of the old B.O.C. races when the idea of allowing movable ballast was being discussed. I always thought that it should be a relatively small fraction of the fixed ballast, say 50%, and be allowed to move no further than, say, 1/6th the length of the boat to one side of the centerline. This, I thought, would allow adequate performance enhancement without ending up with ballast sponsons and extreme beams.

    What the B.O.C. race people did, however, was merely stipulate that the moveable ballast should not incline the boat any more than 10 deg in static conditions. The loophole here, of course, was that a wide, flat floored boat would incline far less with a given amount of moveable ballast than a narrow round or 'V' bottomed one would.

    It wasn't long before this was taken full advantage of. So deep, narrow boats, which are argueably very seaworthy, soon got out classed by wide, deep ones, which are argueably not so sea worthy.

    Hence came the famous (or imfamous) 'open 60's' That look like scaled up Lasers with lead bulbs on their dagger boards. (and now days even they look quaint)

    If the commitee boys had gone with my 'percent of fixed ballast/percent of length' proposal, canting keel boats would have been effectively ruled out of the B.O.C. races. And we probably wouldn't be seeing them now.

    Curious how history works.

    Bob
     
  5. Windvang
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    Windvang Yacht Designer

    Having the pivot higher in the hull also makes it stronger. When you put the bearing at the bottom you have to fair them in, limiting bearing size and material beneath them. The Farr keels hinge between 2 ringframes.
     
  6. Windvang
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    Windvang Yacht Designer

    Ironically the ABN boats have been engineered by a former Ferrari F1 engineer.
     
  7. D'ARTOIS
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    D'ARTOIS Senior Member

    On the contrary- in any respect. More power is required to move the strut; the leverage is substantial ly more and risks of failure are increased.
     
  8. Windvang
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    Windvang Yacht Designer

    Yes, the leverage is higher (unless you put the hydraulics beneath the pivot), but the bearings and the hydraulics (hullside) attachment are one closed system between the ringframes. Usually the shroud loads are also carried to the same ringframes. If the hinge is at the bottom the skin will have to carry the load.

    The ABN's have a similar system with a large diameter drum to fill the gap instead of sliding doors.
     
  9. Vega
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    Vega Senior Member

    Another Farr boat with problems on the keel system:

    “movistar has reported a fault with the port-hand hydraulic ram - one of the two rams that operates the canting keel system. ....They are considering a stop in South West Australia to make an assessment of the damage and a quick repair before rejoining the race to the finish in Melbourne.”
     
  10. Vega
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    Vega Senior Member

    From Movistar, Bouwe Bekking explains, “Last night when sound asleep Pepe woke me up, and told me the news. First I though, “You must be kidding!” It was blowing only 12 knots, and hardly any waves. But when I saw the carnage my stomach turned. Six 10mm stainless bolts had sheared clean off, just behind their heads, and the oil was pouring out of the cylinder......

    Oh yes, all is well onboard movistar, we can still laugh, but need to have a word with some engineers!”:p :p :p
     
  11. D'ARTOIS
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    D'ARTOIS Senior Member

    In spite of all the best designers involved, is no one capable to calculate the real forces that come loose in the canting keel? Point is, theory is useless here.

    Tralalala, who will design the next generation canters? Instead of people who think that they can design soemthing specila, they better go to an aeronautical engineering coy.
     
  12. usa2
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    usa2 Senior Member

    generally they take the peak loadings expected on the keel/rams+ adjacent structure and multiply it by a factor of 6 i think it is. I think the R/P canters have a higher safety factor than the other boats, which is why their only problems tend to be with the diesel getting messed up. IIRC, Nicorette (Simonis/Voogd) also has a higher safety factor.
     
  13. D'ARTOIS
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    D'ARTOIS Senior Member

    That could be very well the case. I have been told, however, that all the main designers, Reichel/Pugh, Farrs and ***.,JuanK; Another designer whose name I didn't pick up and the Wolfson Unit is Southampton had all a finger in the Rulingporridge. They knew long before the rules even came out and into effect what the basic principles were.

    Weights of hull and keel are not calculated separately but put together as a whole number. Therefore, hulls can be made ultr-alight in favour of more weight in the bulb.

    Basically, I do not believe that the calculation for the strength of keel and the reinforcements have been really calculated as there are no references from earlier and similar boats. My idea is that it is not only the weight and resistance statically but the dynamic loads that are the real killers.

    Another point is symmetry. If the keel is not close to symmetric, better say very close, the keel will show a tendency to gu up or down alone, helped by weight and speed, that increases this effect by factor...? Latter issue being never taken in mind, IMHO and therefore those unexpected problems.

    I thinkl even factor 6 is not sufficient. And why factor 6?

    Why not making a scaled version and tankktest it. It's not only Movistar that faces problems, it's Paul Cayard's boat that is felling to pieces, literally.
    Rumours say that this boat is very badly build and came out badly.
    Contrary to that, JuanK's boats are doing quite well and although the race has not run yet, the boats are going better and better.

    So who is to blame?
     
  14. Doug Lord

    Doug Lord Guest

    Doom and Gloom

    D'artois, if you're trying to make serious, meaningfull commentary you should not be so general in your disparaging remarks.Canting keels ,for the most part, have a long and succesfull history. The Farr VOR keel systems seem to leave something to be desired but it is just flat wrong(besides being unfair) to paint all canting keels with the same dour brush....
     

  15. usa2
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    usa2 Senior Member

    factor of 6 is not sufficient. The open 70s rams have a capacity of 100 tons and they are failing. I have no idea why the factor of 6-perhaps its because they figure that a boat in free fall of a certain sized wave would produce a 6G force on the keel.

    Neville Crichton says "We have a safety margin of 3:1 engineered into the boat; it should withstand loads three times those encountered in normal sailing. But the canting keel certainly adds another complexity into sailing and if it fails, you have big problems."

    Im not sure that statement is reflective of the hydraulic rams on his boat-if that statement is true then he's worse off then Skandia, who had a factor of 6 engineered in.
     
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