Mast and Rigging calculations

Discussion in 'Software' started by TANSL, Feb 11, 2016.

  1. TANSL
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    TANSL Senior Member

    For several years I am dedicated to the task of providing the designer of recreational boats, calculation tools that facilitate his work, trying to fill gaps that large naval software development companies do not cover
    So we have developed, among others, the following applications :
    - SCT program for scantlings accordingto ISO 12215-5
    - Spreadsheet to complete the tables in ISO 12217-1-2008.(Now obsolete). In preparation corresponding to 2013
    - Spreadsheet for power determination according to the method Holtrop-Menem.
    - MyR: software for the calculation of masts and rigging.

    SCT also includes various modules to perform calculations ISO 12215-6, 8 and 9. It also has a module for calculating continuous beams and large facilities for manage the various materials used in the construction of modern boats.
    The latest version SCT R.14, in preparation, will include the module MyR.
    Attached is a file that describes the calculation procedures followed by the application MyR. This is not an original method at all, but extracts of texts by other authors. (At the end of the text a reference to the authors consulted is done).
    Certain assumptions have been made on those issues that were not clear but, again, is not a new method but mainly the implementation of the NBS method.
    MyR software, as stand alone application, will be available in a few days to download from my website. For now, overcomingthe difficulties an English translation not entirely correct, I would like to have your comments and criticisms, constructive if possible, on the attached text. With great interest I will answer all your queries. Thank you all for your cooperation.
     

    Attached Files:

  2. quequen
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    quequen Senior Member

    Hi Ignacio, congrats for your MyR module!
    I also made some years ago an online utility for Rig and Mast calcs, I think it didn't become popular because of the extremely tedious input of data. So that's a very important point to take care of!
    I must to update the site because google changed his standards. Table-data are not working right now...

    http://klz-rigandmast.blogspot.com.ar/

    Your .pdf file does not includes mast and boom profiles data. My recomendation is to include some well known mast builders and rigging catalogues, like Selden (attached). The software should pick the best mast and boom profiles (and wire-diameters) for your inputs. (At least, that was the way my online-skedule used to work!). ;)
     

    Attached Files:

  3. TANSL
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    TANSL Senior Member

    Thanks quequen your comments are very valuable. Of course, I will try to incorporate your suggestions to my software. Thanks, again.
     
  4. LP
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    LP Flying Boatman

    This is wrong.

    image.png

    It best to make the forces in your Free Body Diagram agree with actual forces.

    Fb will be a ratio of Fd(DC/BC).

    I've recombined sail forces to act at the CE to save unnecessary work.

    I don't think Fb=-Fd can ever happen unless it's a deck stepped mast and that ain't happenin'.
     

    Attached Files:

  5. Alik
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    Alik Senior Member

    TANSL, thanks for great efforts. It would be great to see something about catamaran masts, those are note covered. Another observation: this NBS method gives exaggerated shroud sections.
     
  6. TANSL
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    TANSL Senior Member

    You're right (I need to think about). I'm not sure that the distribution of the force on the sail, in force at the top and on the boom, is correct. I think that's the real problem to solve. Raise then the equations of equilibrium will be more easy task. So I'm interested in your opinions. Others, such as Mr. E.Sponberg, make other distribution of forces. I have to study the correct way to approach this problem. I will analyze your calculations carefully.
    It is important to know Fp (load on the pintle). That's why we should break down the total force on the sail.

    Alik, thank you for your words. I'll study the case of catamarans. Current study is limited to a few cases of many that can pose a rig. It is generally limited to what the NBS indicates, extending it to the case of three spreaders. NBS method takes many simplifications (eg, a linear analysis of a phenomenon that is three-dimensional) which leads to, as you say, an oversized rig. However, these simplifications achieved that the method is very easy to apply and very suitable for translation into any programming language.
    Classification Societies, for example GL, have matrix calculation methods, more accurate and rigorous but difficult to apply to some not "technical" designer.
    Thank you all for your comments. I hope many more people will be encouraged to comment on the issue.
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    In addition to the comments above, see here:

    Ally design values - Calculating mast and rigging.jpg

    Never ever use UTS values for design. The proof/yield stress is the design allowable value to use. In addition just about every mast is 6000 series alloy not 5000 series alloy in the list. The list also has alloys never used for such too.
     
  8. TANSL
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    TANSL Senior Member

    Thanks, Ad Hoc, for the comments. The list of materials and design stresses are those that ISO 12215-5 standard says that can be used. As I said previously, there are few things of my invention, in these texts. I'll check if I'm understanding ISO incorrectly. Of course, the ISO does not say that these are the specific materials for the mast but the list of the most ordinary materials in the construction of the vessels built in accordance with its standards.
    It is possible that the normal practice in this field says otherwise. I'm trying, as I said previously, assume certain assumptions covering unclear aspects of these calculations and trying to clarify some doubts that the writings I have consulted can pose. I interpret things and ask the opinion of all of you. So I ask you to tell me what in your opinion is wrong and why or what is right and why.
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    There are 5000 series and 6000 series aluminium alloys that can be used, whatever ISO says.

    Masts are made of 6000 series alloy because their unwelded strength is twice that of 5000 series. The masts, in general, are not welded, thus the highest strength alloy is used, that being 6082/6061. 5000 series alloys are not used, not just because of the lower strength (the welded and unwelded 5083-O is the same) but because extruding in 6000 series alloy is significant easier and cheaper. You would find it very very difficult to get any mill to extrude those often tricky mast shapes in 5000 series if at all.

    Thus your list is not suitable and not providing the correct strength for design allowable limits of mast alloy grades.
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    Not forgetting the compression loads from the stays too.

    Not sure where the justification of a FoS of 3 comes from too. This is also not explained.
     
  11. TANSL
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    TANSL Senior Member

    I note Ad Hoc. Thanks for the clarification.
    Excuse me the question, stays should be placed in a "free-standing mast"?. I'm a little confused.
     
  12. LP
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    LP Flying Boatman

    No stays on a FSM. You are correct. I'm sure AdHoc got his wires crosses for just an instant. :D
     
  13. LP
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    LP Flying Boatman

    The sail loading is definitely a distributed load. I made the assumption that the vertical CE is 1/3 the luff length up the mast from the gooseneck (pintle). The distributed load can be assumed to act at a single location when calculating point loadings outside of the distributed load area.

    I've read through Eric's paper on free standing masts that he has so graciously posted here on the forum. He is using the sail CE to develope his heeling arm though he is using the boats CG as opposed to the heel of the mast. He also has a predetermined value for the moment at the deck. He is using the the boats maximum righting moment for each mast and this works out very well for him when developing the safety factor in his mast designs. I think that when he is working up internal mast stresses, he places a force vector at the mast top that will give the equivalent moment at the deck. I'm sure you've read his paper and my point is that there are many ways to skin this cat. The trick is to make sure that the answers you get are the correct answers and not the ones you want to be correct.

    Interestingly, I have been working this problem recently (the free standing mast) and have been considering start to post some of my own thoughts and processes with regard to designing the masts that will go on the boat I am building. One of the functions I am looking at is the loading of the boom on the mast. I'm finding that boom loads need to be considered separately since they typically act normal(90 degrees +/-) to sail loads. I am not sure if any texts I own have discussed boom loads (probably). I have worked through my own calculations and will consider posting them.

    I find that many formulas used in mast design have a lot of cautionary errors that make masts stronger and more reliable. I'm working to lighten my masts as much as possible, for the given mission, but still have reasonable safety margin.

    If you have questions, I will answer them to the best of my ability. This is simply a quest for personal enlightenment for me. I also spent a lot of money on engineering classes and I find the rediscovery of what I know very fulfilling.
     
  14. gonzo
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    gonzo Senior Member

    AdHoc:
    Do you think it would be easier to use the Proportional limit instead of the Yield Stress(Elastic limit) to stay within the linear response area?
     

  15. TANSL
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    TANSL Senior Member

    I'm not Ad Hoc but I hope you do not bother if I respond.
    A study of stress-strain diagrams shows that the yield point is so near the proportional limit that for most purposes the two may be taken as one. However, it is much easier to locate the former. When, in addition, a safety factor is adopted, the difference in the maximum allowable stress value is negligible.
     
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