The perils of edgy design offshore

Discussion in 'Sailboats' started by CutOnce, Jul 18, 2011.

  1. Doug Lord
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    Doug Lord Flight Ready

    Perils of Edgy Weather in Any Boat

    ================
    Thanks, Guillermo-and thanks again for the help. About the openings-I'm not sure those are openings-maybe "Stumble" who has actually sailed the boat could fill us in. I'll PM him.
    Before I'm thru I'm going to get absolutely accurate info on this boat-I hope!


    UPDATE: he didn't know-maybe someone else will....
     
  2. peter radclyffe
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    peter radclyffe Senior Member

    I'd say ,based on what people who have sailed the boat have said, that it is possible the immersed wing(acting like a keel) was an asset and not a liability in this case since it may have prevented the boat from getting away from the crew that were in the water. The design of the boat- allowing it to float when turtled- certainly appears to have contributed to saving the majority of the crew-giving them a ready made raft.


    your reasoning is illogical, if it did not have wings, it might not have overturned
     
  3. Doug Lord
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    Doug Lord Flight Ready

    Perils of Edgy Weather in Any Boat

    ====================================
    I'm not trying to be smartass but if it hadn't been built it wouldn't have capsized either. The wings are an integral part of the design without which this particular boat could not sail in anything over very light air. If the design was changed so that wings were not required for their added power to carry sail you'd have a different boat. I'm sure that now -27 years after this boat was designed- the type could be improved, still be "edgy" and still fit within reasonable rules including those mandated by ORR. By looking at the rules for different types of ocean racing boats including, Minis, Open 60's and multihulls
    I'm sure safety can be drastically improved for the Kiwi 35 and for the type: high performance racing monohulls.
    It will be interesting to see what the sherriffs and the US Sailing investigations come up with.
     
  4. peter radclyffe
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    peter radclyffe Senior Member

    quote
    I'm not trying to be smartass but if it hadn't been built it wouldn't have capsized either.


    even that wing knew when to stop digging a hole
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    Got bored of doing FEA all day yesterday, so i thought for amusement i would have a little "play" with my hydro porgram.

    The below images are very very rough, no claim to be exact nor accurate. But from the principal dim's given on several websites a few figures can be reversed engineered to get a "feel". The hull is shown, just so you can the crude model i did. I was very generous with everything being over pessimistic as such....so perhaps a "best" case.??

    GZ Curve.jpg hull.jpg
     
  6. MikeJohns
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    MikeJohns Senior Member

    Doug you are really going off on a tangent with some of the things you post. People who have sailed the boat don't know anything about its response to an overturning wave, any more than being an airline passenger helps you understand stall aerodynamics.

    The effect of the sudden overturning moment increase from deck edge immersion in a beam on capsize is well described and understood. changing the camber of the topsides to reduce the deck edge drag has a significant effect on the tripping action. This is simple well understood hard fact. So absorb it.

    In this case the deck edge is enhanced, has no hull below it to provide reserve buoyancy and imparts a very high rotational drag. You could get a little more drag out of the wing by cupping it upwards but it does fine given it's existing shape.

    The point where the vulnerability starts is at the dipping of the deck edge which on a design like this is very early in the time frame. The water 'climbs' up over the immersed edge and immediately starts producing significant drag as vorticity in the water behind the sideways translating craft. Add to this the wind induced heel. Any small increase in buoyancy from the immersed wing is immaterial at his point since dynamic forces will dominate the tiny contribution by orders of magnitude.

    It's important to understand that a boat translates (Sway) sideways along with the breaking wave. As I said before the amount of immersed deck edge is a direct and important contributor to the overturning moment in any design but if you stick a huge impeller paddle on the deck edge it's contribution goes off the scale.

    If the wave is high enough on the upper side or breaks and the jet hits the upper extended deck edge there is an even higher and more violent rollover moment. I don't think this case required that but it should be considered that this alone renders winged boats dangerous. The boat we are considering is also abysmal in it's stability, and all factors compound .

    There is no spin you can put on this to suggest that the wings are an asset in a survival situation. They only compromise the vessel , by making the inversion more violent and considerably more inevitable.


    If you want an exercise draw the traveling sequence of a 6 foot wave (short steep sea) and superimpose your cross section of the boat on that wavefront look at the heel angle the wing dips at, that's the start of the augmented capsize moment and the mechanism that starts to resists the boat sliding harmlessly, buoying up and allowing the wave to pass harmlessly.

    While you sketch the cross section look at how the CB moves relative to the projected position of the wave front on the cross section of the hull.

    You need to stop wildly guessing and start to apply some sensible analysis if you really want to understand this event.
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    And then, not forgetting once this wing is in and submerged, that force required to bring this wing out of the water is the ratio of the density of air to SW at 800 times, then the ratio of the area of the wing to the sail area available...in otherwords, you need 800 times the amount of sail if the areas were the same. Even if the wing area was 1/10th the sail area, you're still talking about a force 80 times required...i aint gonna happen!
     
  8. Gary Baigent
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    Gary Baigent Senior Member

    Ad Hoc, I realize that you say your drawing is a rough indication of the K35 ... but you should look again at the rear view photograph of the boat posted on 224: the starboard wing, look closely, has considerably more buoyancy in the area where the flared hull and wings combine - they are not flat wings as you have indicated. I'm sure you will say that is irrelevant, a wing is a wing, but with that buoyancy, the boat at 100 degrees or so, is not going to lie as deep in the water as you have perhaps envisaged.
     
  9. Guillermo
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    Guillermo Ingeniero Naval

    How did you estimate the position of the center of gravity of the hull? Did you include mast, etc?
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    Indeed...but the wings are also not part of the hull, so they are fixed onto the hull, which requires fastenings of some kind and takes up "space" and adds more weight than the wing in the location has buoyancy!. So..swings and round abouts. But if one wishes to be pedantic, all it shall do is increase the peak (GZ) post wing immersion..but wont alter the range...since the deck line remains as it is. You're only adding a small amount of buoyancy in the 40-80 degree range, that is all.

    Looking at this link:
    http://sailboatdata.com/viewrecord.asp?class_id=1014

    The displacment is 1293kg...so the hull only is 794kg. Thus without the 499kg bulb(keel) where would the VCG be?...so the hull has a VCG somehwre in the centre of the hull but a tad lower, owing to heavier skins on bottom and also the sole being low. So this would suggested around 1/3rd of hull depth. Then you have the rudder below...and then the mast and sails above..and sails on the deck bringing the VCG back up again...so very roughly..the VCG could be assumed to be around the deckline.

    From this, add the 499kg bulb, at some 2.0m below the hull. The hull bottom being 0.0m

    That is a pure guess based upon what limited data is shown, as I noted above. Feel free to provide a more "accurate" VCG ...
     
  11. Guillermo
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    Guillermo Ingeniero Naval

    No bulb hull+rig VCG around the deckline seems good enough to me, thanks.
    Now, taking into account your hull+bulb GZ curve, LPS (+/- 130 deg, in the line of Doug's rough estimative) is well over the +/- 95 deg roughly deduced from the ORR's 100 SI figure :confused:
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    Exactly. A rough guesstimate is easy...not an absolute...but a rough idea. So either i have made a massive error and incorrect assumption..or, the data being thrown about (which is very hard to verify anywhere), is not what it claims to be.

    Since once the keel is added...the GZ is as you say...confusing!! :confused:
     
  13. Doug Lord
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    Doug Lord Flight Ready

    The Perils of Edgy Weather in Any Boat


    =============
    Ad Hoc, that is the same link that I used in post number 2-and it is incorrect according to the brother of the owner and Meade Gougeon(see post 143 below):
    the ballast bulb was increased to 1500lb(681.8kg) raising the all up weight minus crew to 3250lb(1477.3kg). Making the hull 1750lb(795.5kg).
    I haven't found any indication whether the carbon mast was sealed or not-could make a big difference as the mast is immersed.

    Pictures-K35 hauled; with port wing folded......
    click on image
     

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  14. Ad Hoc
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    Ad Hoc Naval Architect

    All just hearsay :!:

    Documented independent facts are required...otherwise it is my dog is bigger than yours!! :eek:

    As I said, the curves are indicative...and in no way am I saying it is accurate. Only those clutching at staws are suggesting otherwise....
     

  15. Guillermo
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    Guillermo Ingeniero Naval

    Is that hinged union and the wing fixing mechanism strong enough as to withstand a full inversion without folding? In other words: can at all the volume of the wings be considered intact and in place for stab calculations?
     
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