The roll acceleration: What´s the best for crossing oceans?

Discussion in 'Stability' started by Antonio Alcalá, Dec 18, 2007.

  1. Paul B

    Paul B Previous Member


    Sorry I haven’t replied to you and your boy Willie immediately. I was off this weekend racing on a boat that is similar in size and weight to a TP52, but beamier (B/L = 0.29). No one was in danger of being thrown across the cockpit at any time. No one experienced any snappy vertical acceleration that made anyone sick. In fact, one person who came along was doing his first race, and first ride on a performance boat after years of sailing. At the end his grin was incredibly huge, and he could not believe he had sailed for so long without seeing what it is like to sail on that type of boat.


    Your ilk continue to make misleading statements simply because you can’t compete in the marketplace without dodgy scare tactics. It reminds me of the designer (MSc NA) back in the late 70s and early 80s who wrote an editorial in the publication of the Royal Ocean Racing Club stating only people with NA behind their name should be allowed to design boats. He simply could not compete on the course or in the order books and was frustrated. I believe his statement included something to the effect (paraphrasing here): “I am tired of losing races and commissions to glorified boat nannies.”


    People believe and repeat what they read, and when writing includes exaggerated, inflammatory language like “snap back” it is even more powerful. Of course that is often the intent of the writer. Fear makes it easier to prey on the uneducated. When people write, read, and regurgitate comments about the dangers of “beamy modern boats” they certainly are not actually looking into the facts. But that sort of lemming mindset plays right into your purpose.


    A consequence of the continued publishing of exaggerated BS is unwarranted legislation in the US, EU, and other places. It is a growing trend in the EU across many industries, and a cottage industry has sprung up for people who make their living by limiting our choices and “making us safer.” I am sure you have heard of the most terrifying phrase in the English language, “We are from the government and we are here to help you.” More government intrusion into sailor’s lives is not necessarily better.


    You talk about people not having reasonable discussions with you. It is no wonder, just check your recent record:


    You have posted a ridiculous statement about heavier boats being faster than light racing boats, which you could not substantiate, and when pressed you used an example that showed you either did not understand the difference between elapsed time and corrected time, or you were attempting to mislead. Either way it was unprofessional.


    You have also chosen to post misleading data about the ’98 Hobart, and then disparage people who were there and testified about it by basically calling them liars because their testimony did not support your belief. You pick and choose the data points that bolster your view and ignore those that do not. That isn’t very good science, is it Mr. Engineer?


    You and Willie have quite vocally defended the MCR calculation as a scientific way to compare boats, with others chirping in and reading things into it that are not there. If it were halfway serious about accuracy it would use BWL instead of B. I’m sure even you can sketch up two shapes, one with a wider B and less form stability than the other. I’m equally sure that math/physics geniuses like you, Willie, and the Dr can all come up with dozens of comparisons that show the MCR to be useless rubbish. But you won’t admit it because it doesn’t fit with your argument. Hell, the Dr even modified his reply on that subject because he just couldn’t admit the guy who he was disagreeing with knew more than he did.


    You like to pick racing boats, pushing hard in racing conditions, to try to make your points. We all know the millionaires and billionaires who build competitive race boats do so with winning as the primary design criteria. This says nothing about “light” boats in general, especially in cruising mode. You wouldn’t say all BMWs are unreliable because their F1 cars break down with a higher frequency would you?


    Finally, you have a lot of nerve saying someone is “pretending a superior position.” That is your arrogant, condescending MO, telling everyone how useless the successful designers of the world are compared to your engineering acumen. What a crock.



    The fact is there are innumerable boats of a type you deem unsuitable that have been sailing, racing, and cruising across the globe for 30+ years. There are even examples of well-built, former racing warhorses that have been re-tasked as cruising boats, without the cyclic failures you like to spout on about. Either the designers of those boats have been incredibly lucky, or maybe they were pretty good at their jobs and your assumptions in your calculations are overly conservative?



    By the way, you may want to check the primary definition found here, Mr. Infallible Engineer:

    http://www.merriam-webster.com/dictionary/dampening

    Seems you never tire of being incorrect.

    While we’re at it, maybe you should investigate the difference between “there” and “their” before you attempt to give anyone else grammar lessons.
     
  2. Pericles
    Joined: Sep 2006
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    Pericles Senior Member

    OK, I see PaulB has generously drawn attention to the correction offered by Mike Johns confirming the Mike is correct, but not being able to accept the fact. "Seems you never tire of being incorrect." Well, see for yourselves.

    uote:
    Originally Posted by Paul B View Post
    The drag of the sail is a great dampening device………….

    It’s called damping not dampening (to make wet).
    Sails can also excite rolling. This depends on the course sailed relative to the conditions (wind and sea) levels of parametric coupling etc
    __________________
    Mike Johns.

    http://www.merriam-webster.com/dictionary/dampening

    Main Entry:
    damp·en Listen to the pronunciation of dampen
    Pronunciation:
    \ˈdam-pən\
    Function:
    verb
    Inflected Form(s):
    damp·ened; damp·en·ing Listen to the pronunciation of dampening \ˈdamp-niŋ, ˈdam-pə-\
    Date:
    1547

    transitive verb 1 : to check or diminish the activity or vigor of : deaden <the heat dampened our spirits> 2 : to make damp <the shower barely dampened the ground> 3 : damp 1c intransitive verb 1 : to become damp 2 : to become deadened or depressed
    — damp·en·er Listen to the pronunciation of dampener \-nər\ noun

    Mike Johns is technically vindicated. QED. The PHRASE "dampen down", not the WORD "dampen" is used by an erudite person to describe how to reduce or diminish rolling or as PaulB is doing to me, to dull my spirits.

    Quote:
    Originally Posted by Paul B View Post
    The drag of the sail is a great dampening device………….

    It’s called damping not dampening (to make wet).
    Sails can also excite rolling. This depends on the course sailed relative to the conditions (wind and sea) levels of parametric coupling etc
    __________________
    Mike Johns.

    I am now disinterested in PaulB.

    Pericles
     
  3. MikeJohns
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    MikeJohns Senior Member

    Pericles...............Thanks :)



    The only Boy Willie I can find is the sea shanty (that seems surprisingly apt).


    My Boy Willie

    The night was dark and the wind blew high;
    It was then I lost my dear sailor boy.



    So are you implying that engineers voice concerns just so they can sell safer designs?


    Marketing hype preys on the uneducated. It is wise to introduce an element of caution.


    It’s funny isn’t it , but the lemming mindset is often contemporary culture. The facts are what we want to get to the bottom of, and I like to try and show that some accepted ideas in current trends are not in the best interests of the general yachtsman. In this I am only joining my voice to others many of whom are far more prominent and well educated professionals. These people with funding and resources engage in research and publish papers that you probably have not read.
    What do you think of the recent ‘Maxfun’ debacle that we discussed? The designer was not aware of proper engineering practice and this occurred under current European legislation.
    I said you have avoided discussing issues reasonably as you are now.
    The particular post would be a good reference, In a lot of posts I’ve said that a displacement boat does not have to be light to be fast and that in turn it can be comfortable and have a high reserve strength. If I really said heavier boats are faster it should have been qualified with certain conditions.
    Eh! What’s misleading about that data? Then I was trying to show that a vessel that was supposedly ‘sunk’ in the storm was actually an aged and apparently seaworthy hull-form.

    As for calling people liars; In testimony they stated that they “thought and or believed” that they had a crack in the garboard (but they didn’t find anything). How does suggesting an alternative source of a leak make them liars? This was just weak debating tactics from Chris on a bad day.

    Also I didn’t pick the data points I just posted an analysis that was more ‘scientific’ than Dovell’s and did you have any problem with his vindication of ‘design trends’ (same technique). You are free to post your own analysis.

    Have I really? Would you care to quote me? I thought all I said it was that it was a valid way of assessing certain types of hull-form. If you are not addressing me then please do it directly to the poster concerned.
    Yes there is a question of seamanship there that always flavors the argument. However they are useful as they are illustrative of type in adverse circumstances .

    My beef particularly is with the safety of vessels at sea in the hands of relatively inexperienced family groups. Particularly in heavy weather. Contemporary trends in cruiser design mimicking racing trends has been the crux of many professional concerns recently. A family group is not a hardened racing crew.
    No, your approach is to assume your knowledge and position is superior without entering into any discourse. Assuming a superior position as a debating tactic it is a dangerous gambit if you do not have good solid argument to fall back on. I’ve yet to hear a good solid argument from you.
    This argument is invalid as you cannot assume that those older vessels were under-engineered, nor are we stating the refits, replacements and repairs. In comparison keels have failed recently in both racers and cruisers that were under 1 year old.
    I was trying to give you Engineering not English lessons. I am aware that I make the odd typo.

    Plato said something about the wise who speak because they have something to say and the fools who speak because they have to say something. At times I think I am the fool for replying to these posts.

    Why are you falling on personal attacks and avoiding the specific issues?

    The thread is supposed to be about acceleration particularly incapacity caused by excessive acceleration that light boats are particularly prone to. The larger the mass to water-plane area ratio the more comfortable the motion. If you remain unconvinced of this there are numerable sources you might like to read.
     
  4. Paul B

    Paul B Previous Member

    You just can't help yourself. Crank up the FEAR once more. Now the Max Fun problem damns a whole style of boat? Tell us, how many unmodified Max Fun 35s have had issues? Why not be truthful and tell the whole story? The keel that had problems was not built to the designer's drawing.

    There are other instances of design and engineering problems in current boats, as there have been since pleasure boats have been built. That does not reflect on every other vessel of a similar type.

    It is amazing you haven't dredged up Drum or Smackwater Jack yet. Yes, bleeding edge racing boats have had failures since people first started racing. Same as can be said for auto racing. Neither has anything to do with normal use.

    There was a family mini-van that had a very big problem here in the USA. People died. Why, oh why, did we not ban that vehicle type entirely?

    The thing YOU CAN'T DO is produce actual data showing any propensity of modern boats having the troubles you try to tie them to. Why are you trying to solve a problem that doesn't exist? I assume profit.

    It is a real danger to mislead people into thinking their lack of ability will be overcome by a type of boat.

    I've seen you attempt to damn an entire type based on an isolated incident where the "failure" was due to operator error. You overreach at every opportunity because you simply do not have real data on your side. I could go back and damn you with your own prior posts, but frankly I couldn't be arsed.

    Nothing surprising here. You can't admit any error on your part. "There" to "their" is not a typo. You know it and everyone else does as well, so why try to claim it? Are you that low in self esteem?
     
  5. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    All

    New keels were fitted to every existing boat and the keel design was changed since the keel was also under-engineered. The conclusion was that the keel would have parted anyway from poor design even had the manufacturer stuck to the original design. The designer confused material UTS with Yield and didn't follow any correct design procedure.
    I thought that was interesting and illustrative since it was recent and under RCD directives (regulations) that you were lambasting. Nothing to do with fear on my part but definitely not fun for the dead and apparent that the regulations did not go far enough perhaps?

    Remember that only the keel faults resulting in deaths get investigated and reported officially. Also remember that boats operate in a very hostile environment .

    Ability at sea is variable ( depending on the level of acceleration experienced ability can drop significantly ). Vessel design can certainly compensate for lack of ability. Comfort is a good start (lower accelerations).

    As for ‘facts’ there are numerable papers books and reports that you would find illuminating I would suggest you research and seek out the Southamptom University Wolfston units papers particularly as they have an ongoing interest in vessel design and safety as does my own local Maritime College under Martin Renilson’s efforts . I have many of the papes and I have often quoted from them. I asked you before specifically about what issues you would like to discuss for good reason. Because there are facts studies and papers relevant to those issues.

    Wolfston also have an ongoing program of monitoring local yachting tragedies in the UK. It’s interesting to look at their data. You can contact Andy Claughton for more information, (he is an engineer too). You should also read some Naval Arch books there’s a good one on yachts published by the Wolfston unit as well. Guillermo has already suggested you read Marchaj’s books and I think that would be good for you too.


    Now perhaps we can go on with acceleration and comfort? There have been significant studies on boat motion and it’s prediction even software packages are pretty good these days. Boat motion and human response has been well enough researched.
     
  6. drshaddock
    Joined: Jan 2008
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    drshaddock Design Engineer

    Dampening

    Growing up in the frozen midwestern US, we learned to play a game called Crack the Whip. A whole string of us would hold hands on ice skates, and follow the leader at high speed in a long string until the whole line would follow the leader around a tight curve and the unfortunate soul at the end would go flying off, completely on his own course, usually crashing into the shoreline of the frozen lake. Somehow this discussion, of late, brings that old game into mind, and makes me wonder why we enjoyed playing it.

    Now, then: in PaulB's defense :eek: I feel bound to point out that I believe he was correct in saying "The drag of the sail is a great dampening device" because the first definition in Merriam Webster's was "transitive verb 1 : to check or diminish the activity or vigor of ". And that's exactly what Paul is saying the sails do--they diminish the vigor of the boat's motion. He had pointed out earlier that when the sails weren't up on a boat, it was more lively.

    It's interesting, from the basis of this discussion, that the sails contribute to damping/dampening in more than one manner. The 'drag' of the sail is a necessary byproduct of its lift: the more lift you're getting out of a sail due to an increase in area, a change in aspect ratio, an alteration in draft, etc., the more drag you'll incur as well. That drag is a motion vector, and you could say that the drag vector could either contribute to motion or detract from it, depending on the way the boat is trying to roll. But since the motion vector in this case is coupled to a mass (the mass of the sails) by definition it has inertia, and that inertia, likewise, can either continue a roll that's going in the same direction of the inertia vector, or it can help suppress a roll that's going somewhere opposing it. This is simple physics, but it's tricky because there are four relatively free dimensions to consider.

    There are the three roll axes--yaw, pitch, and roll--plus time, all of which play a part in tearing pieces off boats (okay, obviously hyperbole--rather than saying 'put strain on boats' I'm being dramatic to make a point with more impact) and making human organisms uncomfortable.

    If anybody wants to discuss how hull, keel, and rig interact to affect motion in these four dimensions, I'd love to see it. I thought that was what this forum was about. I'm not out to sell any designs--at my age, my interests lie in several directions: one is to design and build the boat on which Jeane and I will retire soon and visit the world; one is to help a good friend built a raceboat, an i550 (one of those light, beamy extreme designs, just because it's fun); and a third is to try to contribute to and learn from discussions of boats in general. My first degree was in architecture, and I thought buildings were complex things to design; one had to keep so many factors in mind to ensure that the inhabitants would be safe, comfortable, and be able to afford it. I thought there were so many compromises to make. And then I discovered boat design, and realized I'd been living in ignorance. It's a much more complex environment, and it can be much more hostile.

    Back in 1980 I got my first pilot's license, flying in a small Cessna. I was amazed at how much more difficult it was to navigate in three dimensions, dealing with yaw, pitch, and roll, and trying to keep it all coordinated as you looked down upon the world from two miles up through the haze. But with boats, my friends, you're dealing with three dimensions but in a way it's more complex--the fluid below you is rather different from the fluid above you, and you are buoyant, hopefully, existing at the interface between the two of them and affected in the extreme by both, while trying to spot and interpret land masses seen only on edge and navigational markers from a distance, while you're cresting the waves. I'm trying to make the point that this is a very complex subject; ideas and theories and directions have changed many times during the last century and there is every indication that they will continue to do so. That means that none of us has all the answers. I'd love to see this forum discussing those theories and ideas rather than dealing with frustration and attacking others without cause and worrying about whether an accidental word substition is a typo or not.

    My spirits are pretty dampened right now. But this is still better than the political discussion on Sailing Anarchy;)
     
  7. Paul B

    Paul B Previous Member

    Be aware that there are people out there who would like to keep you from doing that. In order to keep you "safe" your freedom to design the boat you want will be removed. There is an agenda in a lot of this "unsafe" nonsense.

    You will note there is a lot of talk about how unsafe some design types are. However, as you have seen there is little real world data to back any of this up. I have asked multiple times for this data to be presented, and nada. It sure makes good copy in certain magazines and on discussion boards, but then again hype and exaggeration always do.

    There is a lot more danger in riding a rice rocket or flying a Cessna than there is in cruising your Pogo 40. Hell, there is more danger in driving yourself to the marina in the family sedan. Yet you are still able to choose to do these things.

    We don't need more nanny state. If you can't sail well enough you have no business endangering your family in any sort of vessel, just to satisfy your dreams or ego.


    I do have to thank you for having the huevos to make the statement you did in your post.
     
  8. Guillermo
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    Guillermo Ingeniero Naval

    Sheriff Cooper, Sheriff Cooper,
    Lola wasn't killed by me!
    I'll come down from Ruby Mountain, Sheriff Cooper
    But I'll not commit suicide!

    (Tell Them Willie Boy Is Here, PaulieBee. :D )
     
  9. Guillermo
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    Guillermo Ingeniero Naval

    Antonio,
    I think you'll be interested in the reading of this paper I came to know thanks to our fellow member Kay 9 in these forums
    http://www.nps.navy.mil/orfacpag/resumePages/projects/Fatigue/HSISymposium/cdr_pdfs/indexed/1a_3.pdf
    From there:
    "McCauley and O’Hanlon quantified the severity of the effects of motion by determining the incidence of vomiting as a percentage of those exposed to motion, and labeled this result Motion Sickness Incidence (MSI). They found that the vertical component of motion was primarily responsible for inducing motion sickness, with little or no effects from the pitch and roll motions, and that the maximum sensitivity to motion sickness occurred at 0.167 Hz (Griffin 1990)."
    Having a simple parameter, or ratio, to roughly but quickly evaluate the heaving response characteristics of a boat, such as the widely accepted MCR, is of interest and useful for cruising people.
    Cheers.
     
  10. Guillermo
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    Guillermo Ingeniero Naval

    On the other hand, heaving motions can induce parametric rolling in waves due to a periodic change of the position of G in relation with the average water level. The rapidity with which parametric rolling develops greatly depends on initial value of heel angle and the amplitude of heave. This is of special importance in a situation when synchronous rolling has already developed, which may lead to the capsize of a vessel.

    If a sailing boat is overtaken by exceptionally steep waves, when in quarter or following seas, spaced at such intervals that the parametric excitation rapidly amplifies the rolling, it may be knocked down very quickly (even if there is little initial syncronous rolling), when the boat rises leeward heeled to the next wave crest (where stability can be greatly reduced) and her close-reefed sails are no longer sheltered by the upwind seas but are exposed to the full force of the wind. Such behaviour, not infrequently experienced in real conditions, is treacherous and misleading, since in one or two swings the rolling motions may become overwhelming.

    Cheers.
     
  11. Guillermo
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    Guillermo Ingeniero Naval

    Today's quiz:

    Froude’s bucket machine exemplified how the heaving motion can heavily reduce the stability of a boat when in the crest of a wave, due to both gravitational inertia and reduced waterplane area.

    Ted Brewer’s Comfort Ratio contemplates this same physical considerations as it takes somehow into account such gravitational inertia and waterplane area into its formulation.

    MCR = Disp/(0.65*(B^4/3)*(0.7*Lwl+0.3*Lh))

    So, here we have this quizzy question for my pauliebee friends here: could we use MCR not only to evaluate comfort but also a boat's behaviour in extreme conditions? ;)

    Cheers.
     
  12. Antonio Alcalá
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    Antonio Alcalá Ocean Yachtmaster

    Ok friend. I´ve just seen the paper. Fantastic. The best paper in relation with this post since the begining. I´ll imprint and surely it´ll be studied by me in deep.
    But i ask you Guillermo: Are you able to work out a table with the roll acceleration of some boats and their classification in severe,moderate and low MSI?

    I know it´s a hard work, but it will be great, and we´ll get the goal of this post: i mean, knowing the differents types of boats according to the MSI and the direct relation with the MCR and at the same time with the sailing performance. Which of one is the better for crossing oceans.

    Best winds
     
  13. TeddyDiver
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    TeddyDiver Gollywobbler

    I'm my opinion the formula shoud give credit for narrow hulls, or in other word, longer hull forms. In this regard long overhangs should anyway be punished. So is there formula for OCR (O for Ocean)

    OCR = Disp/((B^4/3)*(Lwl^1/2*(Loa-Lwl))
    :cool:
     
  14. TeddyDiver
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    TeddyDiver Gollywobbler

     

  15. Guillermo
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    Guillermo Ingeniero Naval

    Antonio,
    I'm afraid I have very little spare time these days, as my job is demanding a lot of time and attention. I have this forums' working of numbers "in the fridge" for the time being, except for some ocasional posts just to keep in touch. I have to wait till job becomes less demanding (What I'm looking for is more money and less work, but all I can get for the time being is a lot of work and little money, so the equation is still not the right one at all! :) ).
    All the best.
     
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