deflection

Discussion in 'Boat Design' started by Adarsh Edakkote, Jan 27, 2016.

  1. Adarsh Edakkote
    Joined: Dec 2015
    Posts: 48
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: India

    Adarsh Edakkote Junior Member

    how to calculate deflection of a ship?Is there any software?

    Please advise
     
  2. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 247, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Why do you want to calculate "deflection of ships"?
     
  3. gonzo
    Joined: Aug 2002
    Posts: 14,569
    Likes: 692, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    He probably means the deflection due to wave slamming or uneven loading.
     
  4. TANSL
    Joined: Sep 2011
    Posts: 6,238
    Likes: 301, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    It is not necessary that the slamming phenomenon occurs for the boat suffer deflection along its length, for example. Moreover, I do not think the slamming generate deflection (what is usually meant by that) in the hull. But it is an opinion only.
     
  5. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 247, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Regardless of that, the main question IMO is: why does this guy want to calculate the deformation of the hull?
    I am asking it because his question reveals his apparent ignorance about the common terminology, the methods and tools used. So why on earth would one want to embark on the calculation of ship strength with no relevant basic knowledge in this field?

    If he is an engineer or similar and this is a real engineering task, then I will restrain from answering because an engineer should know where and how to start learning.

    If it is for fun and personal education, then and only then it makes sense. In that case the only reasonable answer is - Adarsh, you need to study the basics of naval architecture first. First learn to walk, and then you can try to run. You can find a good list of relevant books here: http://books.boatdesign.net/

    I realize that this was harsh and possibly patronizing, but that is what I think.
     
  6. TANSL
    Joined: Sep 2011
    Posts: 6,238
    Likes: 301, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Daiquiri, as most of times, I agree with you. But let me be the good guy. Here we are many who say a lot of nonsense, some even pretending to give lessons. Often mistaken telling about an issue that we know but many times we talk about what we don't know and we say many atrocities. Therefore, let Adarsh Edakkote explaining him self at the light of the comments that his question raises, without bothering him too much.
    Apart from knowing why he needs to know what, his question is not absurd.
     
  7. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 247, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    You are right, his question is not absurd. It is actually so basic that a comprehensive answer would be a book about naval architecture and structural design. That's why I advise him to start his research from books.
    But if someone has enough time and good will to write here a forum-format summary of hull design and analysis, he is more than welcome. It is beyond the amount of my spare time.

    Regarding the thing you said about all of us writing a nonsense or ignorant replies from time to time, that is something nobody can deny. For sure I cannot. :)
     
  8. TANSL
    Joined: Sep 2011
    Posts: 6,238
    Likes: 301, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    I am probably one of the most often is mistaken. But I have no problem to recognize when someone makes me realize that I am wrong (at least that's what I think).
     
  9. Ad Hoc
    Joined: Oct 2008
    Posts: 6,644
    Likes: 650, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    D et al,

    There are many reasons why one may wish to establish the deflection of a hull. It is also a relatively straight forward calculation but requires many assumptions.

    The principal reasons would be:

    1) Effect on shaft line
    2) Will windows 'pop' out
    3) Will crew/passengers feel uneasy if decks are moving too much (regardless of stress levels)
    4) Eqpt - will it remain in place
    5) Load paths for stress/fatigue
    6) Modes of vibrations linked to the above...etc etc

    I calculate the global deflection of hulls regularly for the reasons above and many others too.
     
  10. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 247, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    In fact if I knew nothing about that kind of calculations and if it was an urgent thing, I would ask you or another competent person to do the task for me. Or, if I had enough time, I would start studying the naval architecture (which does not mean - gathering bits of info here and there on internet forums) so that after few months I would be able to perform preliminary calculations by myself.
    The question "how to calculate the deflection of a ship, is there any software?" is pretty much like asking "how do I design an airplane, is there any software?".
    But ok, I want to stop being polemic and try to become more constructive. This has never been my style of replying, I guess that getting older is having a nasty influence on my interaction with the rest of the world... :)

    So, my initial question remains - why does the OP want to calculate the deflection of the hull?
     
  11. Ad Hoc
    Joined: Oct 2008
    Posts: 6,644
    Likes: 650, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Agreed. There are far too many such throw away questions here. Tiresome..:eek:
    However, as also noted by Tansl, until the OP replies it is speculative to the reasons why.

    No polemics from what you have written. You're just seeking clarification. But i refer you to this Q to my reply above :D
     
  12. Adarsh Edakkote
    Joined: Dec 2015
    Posts: 48
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: India

    Adarsh Edakkote Junior Member

    Dear All,

    The vessel is an existing wooden dhow.Vessel has deflection of 14 mm.I need to prove it is theoretically.I know the weight distribution along the length and buoyancy.
     
  13. NavalSArtichoke
    Joined: Oct 2013
    Posts: 431
    Likes: 8, Points: 0, Legacy Rep: 83
    Location: GulfCoast

    NavalSArtichoke Senior Member

    A deflection of 14 mm in what length of vessel? How was this value determined? Why does someone think this amount of deflection is unacceptable?

    It's not enough information to know the weight and buoyancy distributions.

    Wooden vessels are tricky to analyze, compared to vessel constructed of metal. You'll need to identify the continuous effective longitudinal strength members in the hull, calculate the moment of inertia using the dimensions of these members at several points along the length, to account for the change in shape of the hull, and then try to figure out a value for the modulus of elasticity of the wood used to construct the vessel. If this vessel does not have construction plans, good luck in trying to determine dimensions of the strength members without taking the vessel apart.

    Assuming all of this information can be assembled, you might be able to make a calculation which confirms the deflection which was measured. If it does not, what do you do then?
     
  14. Adarsh Edakkote
    Joined: Dec 2015
    Posts: 48
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: India

    Adarsh Edakkote Junior Member

    Vessel length is 50m. Class has commented during their inspection and they found out vessel is in hogging condition.
     

  15. NavalSArtichoke
    Joined: Oct 2013
    Posts: 431
    Likes: 8, Points: 0, Legacy Rep: 83
    Location: GulfCoast

    NavalSArtichoke Senior Member

    A vessel in a hogging condition is not that unusual. It depends, in part, on how the vessel is loaded.

    A deflection of 14 mm seems to me to be unremarkable in a vessel which is 50 m long. It's also not clear why class would go out of its way to remark on the unremarkable, unless there is something which they said further that you are not telling us.
     
Loading...
Similar Threads
  1. pyoung
    Replies:
    16
    Views:
    477
  2. Adarsh Edakkote
    Replies:
    15
    Views:
    3,938
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.