Let´s be practical. Are we in the right way?

Discussion in 'Stability' started by Antonio Alcalá, Nov 6, 2007.

  1. Guillermo
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    Guillermo Ingeniero Naval

    Antonio,
    Then I think the deeper keel and its lower weight is though the reason for the STIX being higher than the Beneteau's stated figure of 48. Increasing the keel weight to increase both displacement and gyradius will bring STIX higher, certainly, but as I told you that's not probably easily feasible in my opinion (consulting the manufacturer should be mandatory), so the Hallberg Rassy option seems to me a wiser approach. ;)

    1.- Draught or weight of the keel has no effect on STIX as specific data themselves. Their effect comes by means of their influence on the GZ curve, which is the already given to you by Beneteau (I suppose). There could be an effect due to a lower center of the underwater projected lateral area, which could diminish somewhat the STIX. I have to chek the boat's profile we worked with. I'll let you know.

    2.- The rapid response of the boat is due to a high energy reserve given by the remaining area between the RM curve and the the heeling moment curve of the hit. In other words, at that moment's particular sailing load condition, it's due to the boat's good GZ curve up to the mentioned heel of 45º (big amount of area under it).

    3.- STIX says nothing about a boat's quality of movements and has no relation at all with the MCR. And this last is rather related with vertical accelerations than with rolling ones. The Stability Index, the rolling period T or the Acc figures are the ones to look at for a clue on the rolling quality of movements (Also the Heft ratio). MCR is useful to compare boats of roughly the same size. A 45' boat should move in a 30+ figure.

    4.- The STIX factors just correct the Base Length Factor (What I call the 'basic STIX') which is only a function of LOA and Lwl. Any of them being over the value of 1 indicate more desirable characteristics, and less being under it.

    - FKR reflects the ability of the yacht to spill water out of the sails after a knockdown. You may get a better figure by increasing the RM at 90º or by diminishing sail area or its CE's height.
    - FIR is a measure of the yacht ability to recover after an inversion. Directly related to the AVS and the mass at MOC.
    - FDS is proportional to the area under the righting moment curve over the whole stability range, this is up to the AVS or the downflooding angle, whichever is lesser.

    Generally speaking it's no easy to change an existing boat's STIX, as the affecting factors are closely related to basic design decissions.

    On top of this, I want to bring your attention to the fact that if you intent to alter your boat's assigned STIX, you will need a new CE marking process under Option G, this implying the intervention of a qualified NA, a Notified Body, the National Authority (DGMM), etc, etc. Doable, but complicated and most expensive. Once again the HR option (or the like) smiles under your horizon....:)

    All the best.
     
  2. Vega
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    Vega Senior Member

    Next week I will post the tag that is on my boat, but I believe you are wrong,
    I believe that the tag refers to the load that you can carry over the Minimum Sailing Condition, and I believe that the minimum sailing condition, for a cruiser, includes at least some fuel and some water (half tanks?). It would make no sense otherwise.

    Cheers
     
  3. Guillermo
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    Guillermo Ingeniero Naval

    Paulo,
    The now called Minimum Operating Condition (MOC) at ISO 12217, includes a minimum crew as per the rules (which depends on size), basic sails, liferaft (if mandatory for the category), ground tackle, and a minimum weight for other safety equipment, but no water, fuel, stores or the like.

    The load at the tag is the total maximum recommended load over the lightship condition.

    But, as I'm talking by memory, I will check it tomorrow with the ISO rules before me, and confirm or correct if necessary.

    Cheers.
     
  4. Vega
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    Vega Senior Member

    DanishBagger, if I am saying that I was referring to big (50/ 60f) production cruisers and nothing that I have written implies otherwise, why are you telling otherwise? I find that impolite:( . If I wanted to say otherwise, I would say so.

    Of course, only Condor can speak for himself. I have thought that he was referring to big boats when he said:.
    (but of course I can have misunderstood)

    The more appropriate thing is to ask Condor if I have understood him wrongly and if when he said on a post, tilted offshore, if we wanted to mean that big production boats (like his boat) are suitable as offshore boats, or if he was referring , as you say, to all production cruisers, big and small, being suited for offshore sailing?

    Hei, Condor can you shed some light here?
     
  5. Vega
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    Vega Senior Member

    Bureaucrats are many times stupid, but this is too much. Minimum sailing condition is valid for sailboats and motorboats. If they would not consider any fuel weight as included in the minimum sailing weight how the well they would sail away on a motorboat:p ?

    Cheers
     
  6. Guillermo
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    Guillermo Ingeniero Naval

    Well, STIX and its implications are only applicable to sailing boats over 6 m....
    Motorboats over 6 m length are assessed using their own and different section of ISO 12217.
     
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  7. condor
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    condor Junior Member

    Condor again

    Of course it is only my opinion. As stated, I think modern production boats of any size get negative commentary from old salty dog types who are perhaps out of date. HInckley, Oyster, Contest, etc make great boats. In some respects they are works of art. They are very expensive.

    Production boats, Beneteay, Jenneau, etc. make perfectly fine boats, albeit a bit short on being works of art.

    One of my points is that on balance I would rather be offshore in a bigger production boat than is a smaller boat no matter how wonderful its pedigree.

    1.)Price for price, I think the larger but somewhat less prestigeous boat is a good trade off. For example, I would rather sail to Berumda on my Beneteau 57 than on my friends HR 43. They were about the same price and his boat is a great boat, but 14 feet in my opiniom more than makes up for the esthetic and emotionall difference. Both boats are safe.

    2.) Production boats are all pretty strudy. They do not break and will get you there. As you go smaller, they are slower and the sea motion is rougher. So you potentially are out longer having less fun if it is rough.

    3.) I enjoy this dialoque, it is helpful for upcomng articles I am working on.

    4.) Boating in anything not patently unsafe is fun, and I think well of fellow mariners. These opinion pieces are just ruminations and nothing more. There is no right answer and I am not particualrly strident about my point of view.

    5.) Boating is changing. Modern equipment, GPS, radar and auto pilots make the sport much safer than it was even 15 years ago.

    6.) Part of the change is the quality in production boats. It is a very competitive market, only the strong have survived. Some of these boats may not be your cup of tea, but they are almost invaribly safe and strong. I have yet to see a Hunter, Catalina, Beneteau, Jenneau:
    Dismasted
    holed
    sunk
    lose a chainplate
    lose a shroud
    injure its crew because of a boat failure (cut and bruises not counting)

    In fact, I would almost hasten to say that the opposite is true. These boats collectively seem almost bullet proof and idiot proof (lots of testing in the charter fleet).

    Condor
     
  8. Guillermo
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    Guillermo Ingeniero Naval

    Condor,
    As I'm joining as much info as possible on these matters, I'm most interested in knowing your article. Would it be possible to get from you a copy in PDF format or whatever?
    Thanks in advance.

    Cheers.
     
  9. Vega
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    Vega Senior Member

    Antonio,
    It would have a variation if the ballast was the same. But that is not probably the case. The designer will had more ballast (in your case 350kg or so) to compensate the higher position of the ballast. In the end both boats will have the same center of gravity and very similar RM curves. Normally both versions have the same STIX and if not the difference is really minimal, never a significant difference as it is the case.

    If you have a look at the curve that was provided to you, you will see a regular curve with a bump (90 to 100º). That bump is due to the cabin. The bigger the cabin, the bigger the bump and the bigger the effect on the inverted stability. I mean, you will have a bigger AVS, a smaller inverted stability and also a better final positive stability. That’s why those small life-saving boats (that have no inverted stability) have a cabin that looks like a WC cabin:D .

    Some years ago the stability curves that were provided didn’t have that bump. They didn’t take into consideration the effect of the cabin. STIX calculations were made taking into consideration those curves.

    If you pick that curve and take away the bump, continuing the line, you will see that you will obtain a 119ºAVS, if you continue that curve you will also have a lot more of inverted stability.

    If you consider that curve for calculating the AVS, I believe you will obtain 48.

    In the last couple of years, the curves I see have all that characteristic bump and the AVS considered on the calculations is the AVS you obtain with that curve. I think that now they calculate the STIX with that curve, and that will provide a higher STIX.

    Your boat was certified when the no-bump curves were used, so the certified values are AVS 119º, and 48 STIX. But if it was certified now, they would use the curve given to you by Beneteau, and the AVS would be 126º and the STIX higher.

    About the other questions, I will try to answer when I have more time available.

    Regards
     
    Last edited: Nov 12, 2007
  10. Guillermo
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    Guillermo Ingeniero Naval

    Paulinho,
    As always when talking stability, you have no idea of what you're talking about.
    The systems that did not take into account the over deck volumes were IMS, SSSN and the like, never STIX.
    If you take a curve 'without the bump', with higher inverted stability and lower AVS as you say, you will get an smaller STIX, not a bigger one.
    Please don't play NA anymore, it's totally ridiculous.
    The 'curve with the bump' was the one I used to calculate the STIX 51 figure. If you think I'm wrong, please do the calculations by yourself and find out if there is a mistake, instead of stating nonsense. I'll be grateful to learn.
    Thanks.
     
  11. Guillermo
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    Guillermo Ingeniero Naval

    Condor,
    As many other boats, those have had they share of structural problems. I suggest you to ask the insurance companies or their surveyors.

    Cheers.
     
  12. MikeJohns
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    MikeJohns Senior Member

    I think you are drawing conclusions from very skewed data.

    Charter fleets operate in and restrict charterers to predictable safe conditions and areas. Insurance companies bearing the brunt of the claims have severely restricted the areas and seasons to what they consider profitable risk. Even then your insurance fee will be quite high.

    If you look at the insurance claims from that charter fleets you will apparently be surprised. I do insurance reports and I have my share of horror stories.

    From what we would consider normal use I have seen failed chain plates, hull-deck delamination and bulkhead-hull seperation, failed P brackets and failure of the laminate around the rudder shaft entry.

    From accidental damage, grounding damage can be considerable, keels, hulls and rudders from underwater collision and delaminated topsides and considerable flexure damage to interior furniture etc from coming alongside too hard and fast. A lot of grounding damage is from dragging anchors , rudder shafts are often bent and the rudders themselves are very vulnerable.

    Look at the cyclone damaged vessels in the US for good illustration of ability of hulls to resist damage.

    Charter operators often buy very poorly suited boats for inexperienced operators but they are tied into the whole marketing hooplah too.
     
  13. Antonio Alcalá
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    Antonio Alcalá Ocean Yachtmaster

    Having the point Guillermo or Vega, the true is I´m learning in each post some about concepts of stability and anothers. Thinking that it´s the way to the deep knowlegde of sailing of the most of navigators I strongly suggest to carry on diving in the reactions of the boats in rough sea, this is real and this can to help us in taking into account decissions in oceans. And, I strongly suggest too to leave disagrees finishing in personal disqualifications. They don´t help anybody, only to the particular ego of each one.

    I think everybody has something to contribute here

    Best Winds
     
  14. DanishBagger
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    DanishBagger Never Again

    So, Vega, do you still think that Condor's merely talking about his own boat, that happens to be a production boat?

    And, that you, defending his position weren't agreeing with him about production boats as a whole vs any boat under 35 ft?
     

  15. Antonio Alcalá
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    Antonio Alcalá Ocean Yachtmaster

    Now I bring your attention please:

    Somebody has offered me 3 posibilities for changing my 473.

    1.- First option: 1984 Hallberg-Rassy 49. No comments Everybody knows it

    2.-1989 Formosa 51 Ketch. I´d like comments about her. Excellent MCR but not a great sailing performance

    3.- 1989 Diana 60 ( Tayana) sloop rigged. Excelent condition ( I saw her)

    4.- Grand Soleil 53 , 1992 model GS 52. German Frers Design


    My intention is getting a boat with total security for crossing oceans in any weather condition, but attention: sometimes "solo" andsometimes with my family, I´ll choose depending on the forecast the adequate course avoiding bad conditions.

    Waiting your responses

    A.
     
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