Grimalkin IS a good design

Discussion in 'Stability' started by Mik the stick, Sep 9, 2014.

  1. MikeJohns
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    MikeJohns Senior Member



    Looking at Loki. Here's the interview:

    I don't think it went to 180...... but whether it was...... I would say somewhere between 130 and 150. That would be my guess.

    Now , did she come up fairly quick?

    My feeling on that is that it was about 10....15 seconds.....and you know it's hard to judge.......

    But we're not talking minutes here ?

    No


    So Loki sat inverted past her LPS until another wave righted the boat, that's an inversion not a knockdown by any assesment.
    They were lucky that another wave righted the boat reasonably quickly as with a LPS of 115 and with some flooding from a broken portlight it could easily have been many minutes. The flooding and some bouyancy of above deck gear also is likely to have given the inverted list.

    Any argument that this was not an inversion is disingenuous. Once again looking at the plot below, Loki is a as pretictable a casualty as Grimalkin.
     

    Attached Files:

  2. CT 249
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    CT 249 Senior Member

    Oh come on Mike, to do things like calling someone "disingenous" because they dare to happen to use a common word with no proper definition in a different manner is just silly.

    The term "inversion" the term does not appear to be defined in this context. I note that Claughton, who you have referred to specifically, did NOT refer to passing the LPS as "inversion" in his summary of his research. Claughton in fact specifically wrote that he avoided defining the related term of "capsize" because "the behaviour of the models could not be compared on a simple capsize, yes or no basis".

    Given that there is not apparently any generally accepted definition of "inversion", that the general English definition is too loose to be useful in this context, and that authorities like Claughton use a different term for the area beyond the LPS and state that related terms cannot be clearly defined it appears that there is nothing disingenous about believing that "inversion" means rolling further than 150.

    Re "predictability"; as noted earlier, it appears that boats with an LPS over 130 were just as likely to roll in the '98 Hobart as boats with an LPS under 120. How does that correlate with the "prediction" that boats with a lower LPS are more likely to invert?
     
  3. TeddyDiver
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    TeddyDiver Gollywobbler

    So you are doing the same now you accusing Mike of. For a boat with ample amount of righting arm left "knocked down" aren't "rolling" in the sense you are using the term in this context. How would you like to call a state where a boat is at or over AVS and has difficulties righjting up then (or any of the terms in " ")?
    It has been said before in this thread and obviously it has to be mentioned again that the time it takes to recover from a knockdown or if there's a dangers to "turttle" is what matters most,
    BR Teddy
     
  4. CT 249
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    CT 249 Senior Member

    Yes, I'm aware of the use of casualty analysis - I just wanted to know the dataset, as the Taylor data managed to miss the well-documented inversion of Solandra, the S&S 34 and a boat that had a very high LPS.

    It's interesting to note that 47% of the small (Class V) boats in the 1979 Fastnet reported being knocked down to the horizontal or close to it.

    The following "Grimalkin types" (ie light to moderate displacement half tonners) can be identified as having raced in the '79 Fastnet;

    Nicholson Half Tonners - Beep Beep, Grimalkin
    Hustler 32s - Xaviera, Gunsmoke, Ossian, Karibariou
    Shamrocks - Rapparee, Mossick Alma, Silver Foam
    Custom Peterson - Green Dragon
    Contention 30 - Tarantula
    Lees 30 - Pinball Wizard

    Six of the 12 (50%) rolled beyond 90 degrees.

    There were 11 Contessa 32s in the race. Five of them (45%) rolled beyond 90 degrees.

    The 22 other small Class V yachts of in the race were apparently mainly "classic" designs such as S&S 34s (LPS around 130) and older half tonners, probably with a similar LPS. About half of them rolled beyond 90 degrees.

    Therefore the Fastnet report indicates that the chance of a "Grimalkin type" rolling beyond 90 degrees was basically no higher than that of a "classic type" of small yacht, including the Contessa 32 that was used as a comparison in the Wolfson tests.

    Yes, the chance of a long and "full" inversion in a Grimalkin type is higher than in a Contessa style boat (or my own half tonner) but the reality is that decades of experience indicates that we are dealing with a problem that has occurred about three times in some 40-50 years, in which time "Grimalkin types" have sailed many, many thousands of sea miles.

    To effectively ban such boats, forcing people into bigger and more expensive yachts, is arguably a very poor way to react to such an extremely rare event. We don't normally spend very large sums in order to cause a small reduction in an extraordinarily rare event so is it so wrong to ask whether we should do it in sailing?
     
  5. CT 249
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    CT 249 Senior Member

    1- Yes, there appears to be no common, clear and accepted definitions and terms for "rolling", "inverting", "knockdowns" etc.

    All that Mike had to do was say that he and I have different personal understandings of these loose and undefined terms. He didn't have to accuse anyone of using such terms in a "disingenous" fashion.

    2- I don't think that I ever said that rolling/inversion/passing beyond the LPS wasn't a bad thing. It IS a bad thing. However, where is the evidence that it "matters most" in the overall scheme of the safety of offshore sailors?

    The vast majority of inversions don't lead to death or boat loss. The biggest death toll in major ocean races has to liferaft failure. Eight people in Fastnet '79 were killed by hopping into rafts that failed. They did so because they were felt that their boats would not survive another roll. In all three cases, the boat actually DID survive the storm even when left untended.

    Fear of the possible consequences caused more deaths than the reality of what actually happened.

    I'm not saying the fact that small, light boats are (all else being equal) more likely to invert if struck by a wave should not be recognised. All I'm saying is that the reality is that this issue may receive too much attention given the fact that it is an exceptionally rare event and that even larger, more stable boats can suffer disastrously in the same conditions.

    I don't like to talk of the nanny state mentality, but when it comes to banning boats because of one incident in almost 50 years, it does look like that sort of over-reaction.
     
  6. MikeJohns
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    MikeJohns Senior Member

    You asserted that Loki didn't invert. Based on what .....the inverted boat reportedly having a list, and that inversion isn't well defined ?

    I called it disingenuous because I presumed you knew enough Naval Architecture to understand the difference between inverted and upright. I'll quote Marchaj:

    "The very essence of human predicament is the split between reason and belief - the first is controlled by the rational mind, the second is governed by emotions and ideologies. Belief tends to distort reality via interpretation by frequently aggressive dominant minorities, into something acceptable to them.
    This is not to say that such people are self-consciously deceptive. They simply propagate belief, or rather perverted logic, which they may not themselves hold self-critically. "

    Marchaj also noted similarly that ideology, belief and even self interest tended to bias peoples recollections of events.

    We know the mechanisms by which a boat is capsized. We know the characteristics that a boat should possess for best survival in extreme conditions. You can acknowledge these and more sensibly argue that prompt rescue and good forecasting reduce the risk. Then skippers can acknowledge that their boats are not suitable for heavy weather and they can avoid it.

    Eventually the Nanny state is created by the racers predicament for competitive boats. Mix small competitive boats with heavy weather and predictably casualties ensue, again and again. That's why the CYC was found to have failed in its duty to manage the 98SH race. Ultimately if you let marginal boats compete you have to limit the weather criteria for the race.
     
  7. MikeJohns
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    MikeJohns Senior Member

    As for knockdowns, inversions and creative overlaps of the two cases, it would be better if we use the following:

    B1 knockdown : within LPS recovers.
    B2 Knockdown : Proceeds past LPS and is rolled over, ie inverted.

    In a cresting breaking wave the volume of the jet of water is proportionate to the wave height. This jet delivered against the boat, produces the subsequent overturning moment. It's been shown that a wave height of one half the boats length and fully breaking ( research has shown that it's actually 0.55 L) is sufficient to overturn any craft struck fully beam on. But that's a scenario all helmsmen avoid. That just means all boats are at risk in heavy weather if they are beam on to significant fully developed breaking waves.
    But there are two issues; vulnerability and probability. All small boats are vulnerable in heavy weather and much can be made of isolated incidents of seaworthy boats rolled to supposedly prove or disprove some theory. In reality however the smaller the boat the higher the probability that it will encounter a wave which will impart enough rotational energy to cause B2 inversion. Even when it's being helmed with care.

    There's a whole gamut of possible encounters with the breaking crest that avoid the full force and reduce it to a partial and safe encounter. However that might still be sufficient to overturn a small boat. That makes it a much more statistically likely encounter for smaller boats. There are also several mechanisms related to boat wave interaction that make inversion more likely for certain types of boats. Risk of inversion can be reduced by a variety of tactics and by design but LPS has been shown repeatedly to be by far the most important design feature. That's why smaller boats should have a higher LPS than larger boats.


    B1 knockdowns are not vessel casualties. A boat with a healthy LPS can be knocked down well past 90 degrees and still be a B1. The slope of the wave keeps the rig out of the water and the boat recovers intact and undamaged because it has sufficient reserve stability. The boat recovers immediately, doesn't flood and seldom loses it's rig unless it's scantlings are deficient.

    A B2 knockdown is extremely dangerous, usually leads to major damage, significant flooding, drowning of crew, incapacity of ancillary equipment. More importantly it usually leads to the loss of the rig which remains attached and can cause more subsequent damage the boat. The ballasted sailboat sans rig has a debilitating unsafe motion from the large reduction in roll gyradius and is at a much greater danger of being re-inverted.

    [FONT=&quot]Whether a significant wave encounter results in a B1 or proceeds to a B2, depends on the final angle of knockdown, and the area of the RM curve from the subsequent knockdown angle to the LPS.

    [FONT=&quot][FONT=&quot]Incidence of injuries and MOB can be high in knockdowns amongs racing crews [/FONT]especially [/FONT]when precariously perched on the rail. It can also be very detrimental to stability once th[FONT=&quot]ey are rotated past the center of buoyancy and produce a significantly large decrease in [FONT=&quot]LPS[/FONT]. [/FONT]
    [/FONT]
     
  8. CT 249
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    CT 249 Senior Member

    The RORC, who seem to have created the B1/B2 terms in this application in their 1979 Fastnet report, did not include any reference to LPS in their definitions of B1 and B2. They classed knockdowns to horizontal as B1, and knockdowns that "beyond horizontal" or "substantially beyond horizontal" as B2.

    If you called me "disingenous" and "creative" because I dared to have a different personal definition of the undefined term "inversion" than you, it could be called "disingenous" and "creative" of you to take terminology that was popularised and (AFAIK) invented by the RORC and decide to re-define it. Let's instead say that it's good to see that you have actually got to the stage of defining terms instead of insulting those who have different definitions

    Yes, bias is of course an issue in matters such as these - but there is room for allegations of bias on both sides. For example you claimed that Dovell's analysis of the '98 Hobart was biased but have provided no reasonable explanation for Taylor's failure to include the B2 capsize/inversion/roll/knockdown of the S&S 34 Solandra in his chart. If Dovell is to be criticised for bias then why not Taylor, who made such an odd omission? Why is Joubert, a designer and a professor of engineering who said that any boat could have been rolled in the '98 Hobart, ignored in favour of those who were not there?

    Yes, the mechanisms of knockdowns are recognised. Yes, the fact that small boats may in some ways be more vulnerable to them are recognised. Yes, the fact that a B2 normally causes serious damage is recognised. In that case how can one ignore the fact that boats with a high LPS, such as Solandra, Solo Globe Challenger, Sword of Orion and Miintanta, had just as high a chance of suffering a B2 in 1998 as boats with a low LPS?

    The fact that a smaller, lighter and beamier boat is more vulnerable to being rolled past the LPS may be accepted but that cannot obscure the fact that decades of experience have proven that any extra vulnerability of "Grimalkin type" (ie light/moderate displacement 30 footer) cannot be very high because they simply do NOT have a markedly inferior record of safety (in terms of crew casualties and boat loss) than many other types. Despite the claim "Mix small competitive boats with heavy weather and predictably casualties ensue, again and again", Grimalkin types have been exposed to heavy weather and have NOT suffered casualties again and again - in heavy weather events like the '77, '84, '93, '98 and '99 Hobarts and many Fastnets bar 1979, the Grimalkin type of light/moderate 30 footer has not become casualties, nor have their crews.

    To effectively ban a type from long offshore races when the facts are that years of experience have shown that the type does NOT have a higher casualty record than other types may well be seen to be a poor decision.

    It is easy to argue that there is a major problem with the design of modern offshore racing boats, because the death toll caused by the loss of high-aspect bulb keels is staggering and completely out of proportion with any other cause of death in the history of the sport. The toll taken by Grimalkin types is negligible in comparison to the number who have died aboard boats with much higher LPSs, whether of light or heavy displacement. The statistical evidence indicates that there is no significantly higher chance of death if one steps aboard a Grimalkin type for a long ocean race.

    In the end the basic issue that is that any theoretically greater risk to crew of Grimalkin types has been proven by the years to be so small that banning them is arguably an over-reaction. We do not and cannot ban everything that poses a risk to safety; otherwise we would ban cruising in all types of yacht, bushwalking, cycling and innumerable other leisure activities.

    We must and do use cost/safety analysis when calculating safety requirements and in this case, any reduction in safety is arguably not worth the general cost involved in banning boats of this type from major offshore races. To completely ignore the downside, as has been done repeatedly, appears to be rather odd.
     
  9. MikeJohns
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    MikeJohns Senior Member

    That's why I defined them for the prurpose. Whether a boat is disabled and becomes a casualty or simply recovers and sails on depends very much on the definitions I used.

    A comment on the logic of an argument is not an abusive ad-hominem no matter how much you try and spin it into one. If you look you'll see I said the argument was disingenuous. Later in this post I'll use the term a 'flawed argument'. I'm not saying you are flawed, you need to exercise emotional detachment from a technical discussion.

    All boats can be inverted to B2 as I just said in my last post, but I also said there are two issues vulnerability and probability. Various research facilities around the world (not only Wolfston) have now shown the link between the probability of B2 knockdown and LPS. In fact Wolfston thinks their guide might even need to be adjusted upward as future statistics unfold. So far it's the best guide produced of an absolute minimum LPS for an acceptable level of risk.

    Dovell as the designer of one of the casualty boats in the 98SH was hardly an impartial expert witness and could certainly be accused of bias over his initial interpretations of his statistical plots.

    Importantly world leading experts on small sailboat safety exist who have no bias. The very people who produce the factual research are also scathing of racing yacht stability.

    Here's Barry Deakin from Wolfston commenting on boats in the 1998 S-H

    "........ yachts which are excellent in some waters but shouldn't be regarded as a safe place to be in, in a storm in the ocean.
    I've been working on this subject for a long time now, about 20 years, and I've always been surprised at how little notice has been taken of the research. .......... the research has been done by more than one organisation and, and still very little account seems to be taken of it in some circles, and there are certain members of the industry who are striving very hard to raise public awareness and there are people who, who are obviously driven by market forces and, and are being driven in the opposite direction by those market forces, so I think it's disappointing that the public are being misled still about the level of safety of the boats that they're buying....."


    Cost analysis ? Surely human risk analysis is the issue. Again that's why the CYC was found to be at fault, it didn't cancel the race and instead let unsuitable boats proceed to their doom.

    Don't confuse a managed race with weather restrictions and safe havens with the suitable characteristics of an ocean cruising boat. Skippers in the S-H expect that their boats will be suitable for the conditions the CYC lets them race in. That's the nanny mentality. It's a shame because the really tough storm safe boats cannot show their merit.

    I explained before that human casualty analysis is a flawed argument ( note the argument, not you ) . Racing boats with large numbers of crew on deck, even perched on rails in heavy weather will get thrown about and injured, it's highly likely, which makes a B1 knockdown so significant for racers in terms of human casualties. Also retirements to a safe haven, and helicopter lifts of scores of people also change the stats. Neither safe haven nor shore based helicopter services nor fleets of naval craft and fishing boats are available to assist a boat in crisis in mid ocean. A boat like Grimalkin, or Loki or Taka or even Winston Churchill are all too low in stability for their size to be considered really safe choices for storm conditions.
     
    Last edited: Oct 7, 2014
  10. Zedwardson
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    Zedwardson Junior Member

    I registered to post to this thread actually...and I am the first one to say most on this thread have forgotten more about boats then I know....


    Isn't the point of the reason why the Contessa 32 in the Fastnet or the Orion in the S-H are viewed as much better designs then say, the Grimalkin or other boats that are viewed poorly for stability safety is not that they won't be knocked down or capsized (as small boats may encounter a wave that will cause a knockdown or capsize not matter how stable it is) but in the righting ability to get upright in a timely fashion so that the crew does not drown and limits the time water can enter the cabin area to prevent flooding that may cause the boat to take on tons of water and or sink? If I recall correctly the Contessa 32 that finished the Fastnet did state they where knocked down at least on one occasion but it promptly restored itself to its correct heel and did not lose the rigging in the process...
     
  11. MikeJohns
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    MikeJohns Senior Member

    Welcome to the forum!

    A B1 Knockdown is not particularly remarkable and is a common enough event in heavy weather a rig might survive numerous B1 knockdowns without structural problems. Inversion (or B2 knockdown) is the really dangerous event. Not only does it lead to injury but deep immersion of the rig while the hull is rapidly rolling usually destroys the rig and often the excessive loads from the stays can damage parts of a weakly built hull.

    The greater the area in the static RM curve from 90 to LPS the more resistant the boat is in wave impact to proceeding to an inverted state or a b2 knockdown. It's all about the amount of energy required and the time the wave has to act on the hull.

    The other issue is the time inverted which is a statistical likelihood of a wave encounter with a large enough wave to roll the inverted boat upright. The static LPS of a monohull sailboat is a reasonable indicator of the time this takes. At 150 degrees LPS and above there has been shown to be no stable inverted state and the vessel instantly recovers, below an LPS of 150 degrees the time to self recover rises exponentially as the LPS reduces. At 110 degrees it's very likely that you will drown if trapped or unconscious on deck before the boat recovers.

    The predicted time inverted is just a statistical likelihood ( or rule of thumb) that a sufficient wave will be encountered that can overcome the crafts inverted stability. It can take longer or occur much quicker if lucky.

    Sometimes a low LPS boat may not recover at all, because it was inverted by a combination of wind heeling moment and wave action, and the sea state is not sufficient to re-right it.
     
  12. michael pierzga
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    michael pierzga Senior Member

    Many of those old boats with short waterlines , pinched transoms and modest righting moment suffered roll when pushing hard downwind.

    Ive sailed boats of the era for many many thousands of miles at sea. Im sailing a Ron Holland now. Ive covered 300, 000 miles with it...a bit tippy and you get blisters on your hands steering when running hard downwind.

    They're good boats if you reduced power. It would be a mistake to label them unseaworthy.

    Modern boats are much more seaworthy and easy to steer in a seaway.
     

  13. Zedwardson
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    Zedwardson Junior Member

    Thanks, that confirms what I was thinking is that it is important 1) to be stable enough not to be inverted, and 2) if you do become inverted, that statistically the boat has a good chance to quickly turn over again so that no one drowns or if there is damage like the Loki had in the S-H that you flip over before the entire cabin fills with water.

    Does anyone have the curve for one of the 40 foot modern production boats aimed at the charter market that pushes a lot of cabin space as the main driver of the design? Wonder how these would stack up to a Contessa 32 or a Grimalkin.
     
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