Stability criteria for vessels fitted with deck crane.

Discussion in 'Stability' started by athvas, Mar 2, 2013.

  1. gonzo
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    gonzo Senior Member

    A crane with a mobile counterweight may have zero inclination at maximum load. However, the inertia of the crane can compromise the stability of the barge because of rolling and pitching. Static inclination tests may comply with a particular regulation, but may not be sufficient to calculate dynamic loads.
     
  2. TANSL
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    TANSL Senior Member

    The three phrases you've written, no sense at all to me.
    I'm very interested in stability issues. So, my friend, I would be happy if you explain what you mean, so that even I could understand. Thank you.
    Thanks.
     
  3. gonzo
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    gonzo Senior Member

    You may have to study basic physics and marine design. What I am describing is really basic. Can you be more specific about what is that you don't comprehend?
     
  4. TANSL
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    TANSL Senior Member

    Gonzo, explain in English is not my specialty. But I'll try :
    A crane as a whole, has no any other inclination than the one the boat has. The boom of the crane itself that can be tilted independently. Therefore, to say that the crane has no inclination is nonsense.
    The INERTIA of the crane DOES NOT compromise AT ALL the stability of the barge. The suspended load on the crane, with or without inertia, CAN influence the stability of the crane, in amount depending on how and where the weight is suspended.
    Static test inclination, what´s that?, I not know what you mean. I know exactly what is an inclining test by leaning the boat from one side to the other side. It is always a dynamic test. Certainly then inclining experiment can never "be Sufficient to calculate dynamic loads." Only serves to determine the position of the center of gravity of the ship.
    And I do not want to continue teaching you more.
    What you are describing is not really basic, is stupid indicating that you do not know what is physics. You use words from physics but poorly assembled to compose an intelligible sentence.
    I understand you very well and I pity you. Some entity, evil and ruthless, is forcing you to talk about things you do not know and, therefore, you will escape a lot of nonsense. Be strong, Gonzo, shut up, do not write more about things you do not know and that the entity be damned.
    Sorry again for my english.
     
  5. JSL
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    JSL Senior Member

    read "powerabout" again- some land cranes might go to 5 deg. at best, but 2 deg. is common. If pushed past the limit, they can fail in a very impressive fashion and people get hurt.
     
  6. gonzo
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    gonzo Senior Member

    I don't know what your specialty is, but CE standards require both static and dynamic tests. If you don't understand the difference, read these links and educate yourself. Your English is not the problem, your bad attitude is.
    http://www.hellotrade.com/mariner-systems-uk/inclination-test.html
    http://exchange.dnv.com/publishing/rulesship/2011-01/ts401.pdf


     
  7. Boat Design Net Moderator
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    Boat Design Net Moderator Moderator

    It's unfortunate when threads become hostile. Let's please try to keep this thread a productive discussion and at this point not go any further with the jabs or counter-jabs. Thanks.
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    TANSL is simply asking Gonzo to clarify his statement, there is nothing "hostile" in that. The only hostility is in Gonzo's reply because TANSL requires further explanation of what he means, but so far appears unable to provide sufficient explanation to TANSL.

    Do you understand what this is for?..since your reply as noted by TANSL, does not appear to be so.

    When you test a crane, it is, in general, tested statically. That is to say you lift the weight and the weight is held in place. Nothing moves once the weight is lifted and held.

    But when a vessel is in a sea way, that weight is no longer stationary, it is moving, owing to the pitching, heaving and rolling of the vessel, that is to say it is now dynamic (moving). Thus, the weight that was previously static is no longer static and the calculations are void. Ergo how much does this influence the structure? One can perform a detailed analysis to ascertain the actual magnitude the weight now has once the vessel is moving, i.e. dynamic.

    In the absence of model testing or detailed analysis DNV has a simple factor to apply, taken from Rules for Ships Pt.3 Ch.3. Sec.5 A501. This factor can range depending upon the size of vessel, type of crane etc etc. and is applied to the static load. One i did recently DNV required a 1.5 x static load for approval. Since crane foundations etc are now no longer shipyard tested for acceptance. It is now accepted by calculations/FEA only.
     
  9. TANSL
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    TANSL Senior Member

    Thank Ad Hoc.
    Although I can also make mistakes and say the wrong things, I am very picky about the rigor of our opinions. When I do not know about a topic, I do not write on it. I also believe that giving incorrect reviews can be very counterproductive for those who read our posts.
    The work of the coordinator of the forum is very complicated and I appreciate the attempts made to maintain a minimum of education in our expressions. The minimum in terms of technical level, rigor, are harder to come by,
     
  10. gonzo
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    gonzo Senior Member

    Ad Hoc: you don't consider this hostile?: "And I do not want to continue teaching you more. What you are describing is not really basic, is stupid indicating that you do not know what is physics. You use words from physics but poorly assembled to compose an intelligible sentence. I understand you very well and I pity you. Some entity, evil and ruthless, is forcing you to talk about things you do not know and, therefore, you will escape a lot of nonsense. Be strong, Gonzo, shut up, do not write more about things you do not know and that the entity be damned.TANSL"
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Far be it for me to wade into a dispute between 2 posters. However, you do shot yourself in the foot Gonzo. Your posts are ostensibly one liners. Which suggests:-

    1) You have little time available for a proper fully comprehensive comment
    2) You give a brief intro/guidance to see it satisfies and/or yields more questions which you can later answer
    3) That is all you know.

    1) If you have little time available, and unable to supply more info, is it worth posting, as it may not help the poster at all, just confuse them more.

    2) This is generally the route I take. Yet when you are questioned for clarity or to explain further, the replies still remain the same, often vague or incomplete.

    3) If this is all you know on the subject, then being questioned by others with more knowledge/experience , or the original poster to clarify your statement seems to irritate you. There are numerous examples on this website where you have replied in such a manner as noted by this thread alone. Your post in #16 appeared to be too vague for TANSL, so he simply asked for clarification.

    Your response in #18 was dismissive and almost condescending. (Remember many people on here are not native English speakers). If, as you say, it is “really basic”, then surely you would be able to describe in simple terms to the poster what it is …since this is the raison d’être of the website, to help and assist others who are seeking such knowledge which “you” have and the “other” does not have.

    TANSL’s reply in #19 may have been a bit extreme, but it is baited by several other recent exchanges where he has seeked further guidance/clarification from you and your reply has consistently been the same. Very little and misdirection, as also noted here:
    http://www.boatdesign.net/forums/hy...-launching-calculations-46461.html#post618599
    Or here (as recent examples):
    http://www.boatdesign.net/forums/classification/davit-design-46464.html#post618786
    http://www.boatdesign.net/forums/hy...s/definition-planing-45248-40.html#post619483

    Your replies are often vague and seem to totally miss the point even answering questions which were not asked!? So the irritation initiates from your lack of clarification when requested and the other poster being perplexed by your dismissive replies to such requests. Yet like above, why not show how simple and “really basic” such things are, as you cite??..that would help matters and the purpose of this website too. Unless of course you can’t?

    I would say it is a case of the kettle calling the pot black.
     
  12. gonzo
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    gonzo Senior Member

    I can agree with some of your points. However the OP didn't have a problem with my comments. Also, accusing me of being forced by and "evil and ruthless entity" to talk about things is a bit over the top. He has posted in other threads similar things. I don't however agree that stating there are static and a dynamic tests is vague or misleading. TANSL claims there is no such thing as a static test, which leads me to think he has no understanding of the basics. Cranes are always rated to a maximum static load and then de-rated for conditions. For example, wind or sea state will lessen the load allowed or even limit the operation. Another point he became irate and insulting about was when I pointed out that cranes with mobile counterweights produce minimal or no inclination.
     
  13. TANSL
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    TANSL Senior Member

    Boat Design Moderator, I tried to write to you through a private message, but for some reason I can not.
    I apologize to the audience for my sour tone at times. I can not apologize for my technical errors (not intentional), nor for demanding rigor in our opinions.
    Could you, please, try to end it all?. I do not bother too much but we are getting a very low level. Physics is like is and no one can change it at his convenience. For my part, I'll shut up, but keep trying that readers are not confused with incorrect opinions.
    Greetings to all and, again, sorry, not for my words, but the tone of the same.
     
  14. gonzo
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    gonzo Senior Member


  15. Ad Hoc
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    Ad Hoc Naval Architect

    Yes, I would tend to agree with that; it's a bit much.

    But one must also temper it with the non-native English speaker and coupled with that a cultural way of expression oneself. Often "lost in translation", which many English speakers ignore or are ignorant of such colloquialisms, which clash in an instantly globally connected world..
     
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