rigging loads

Discussion in 'Boat Design' started by urisvan, Sep 28, 2010.

  1. urisvan
    Joined: Nov 2005
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    urisvan Senior Member

    hello,
    what are the sources that i can look at for designing the rigging of sailing boats? Also the bigger ones that has 4-5 spreaders
    These are what i have in hand:
    1)Lars Larsson and E.Eliasson, principles of yacht design; it uses Nordic class rules and it is restirected with two spreaders. Maybe the method can be extended to 4-5 spreaders, because it calculates the static transverse rigging loads by taking the RM30 as the designing load. The longitudinal loads are calculated emprically.
    2)Richard Henderson, Understanding Rigs and Rigging; this book is good on recognizing various parts of rigging but does not have an explicit method about calculating rigging loads. they give them as percentage of design force which is directly related to RM30. ( Maybe only this is enough from practical point of view)
    3)i have ordered "elements of yacht design by L. Norman Skene". I did not get it yet so i don't know the scope of the text.
    4)The design of sailing yachts by Pierre Gutelle. there are two books under this name. one is in English the other one is in Frech. The English does not explain the subject. And the other one is in French. Fortunately a friend of us in the forum translated the rigging part of it in English. Does it exist also in English now?
    5)Germanischer lloyd text; this paper shows how to find the forces created by sails but does not include a method to find the rigging loads generated by those forces. It says that it is solved by Finite element analyz. Maybe it can be solved assuming that it is static and then multiplying the result by a safety factor as consideration of dynamic behaviour.

    what i guess is; we should take RMmax as the design moment that defines the force generated by sails. Then find the components of this total force according to different scenerio, so the sail configurations: only deeply reefed main, only foresail, only jib on inner forestay, only storm jib, only spinaker. Then calculate static loads of each rigging part according to these scenerios, and take the maximum ones for each part. Multiply with safety factor.

    Any Standarts, books, texts that explain the calculation process would be very useful.
    Which one do you use in your designs?

    regards
    Ulas Risvanoglu
     
  2. Stumble
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    Stumble Senior Member

    You are going about this backwards. Deciding that you need a 4-5 spreader rig before you have decided on the sail plan won't work.

    First figure out the expected/desired sail area of the vessel in question, then figure out the rig necessary to deliver that sail area. It may be that a 1 or 2 spreader rig is all you need. The generally relavent factors are 1) Height, 2) Width at the chain plates 3) Chain plate position from perpecular 4) Mast material and dimensions.

    Once this is all figured out you start to determine the forces necessary to support the side loading of the mast. Some boats for instance like the Trip 40 have a 5 spreader PLUS a jumper ring rig on a 55' mast because the mast is incredibly thin and week. However I have worked on a boat with a 115' carbon fiber mast that only has 2.
     
  3. urisvan
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    urisvan Senior Member

    yes, you are right, i skip the first stage. please assume that the geometry of the rig has been decided.
     
  4. Petros
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    Petros Senior Member

    This is usually done with design tables such as the Nordic rules because the forces are largely indeterminate. The "rules" were evolved over many years of observations, with very large safety factors because of unpredictable nature of load combination, axial compression and Euler buckling conditions that are difficult to predict.]

    The multi-spreader rig is essentially a multi-loaded truss with nodes that allow moment transfers since the mast is continuous. On modern optimized rigs designed for racing, detailed aerodynamic analysis, and materials shape and properties can be used to determine finite element analysis boundary conditions, and than you allow the software to calculate specific stresses in the assembly. Of course this assumes you can accurately predict all of the possible load combination that might occur on your rig. On racing rigs, they are pressing the envalope to get optimun design, and rig failures are not uncommon when pushing the design limits. On a cruising yacht, you want way more reliability than you would tolerate for a racing yacht, hence the very stout "rules" developed for cruising applications.

    You can develop your own stress analysis process, perhaps using an excel spreadsheet to do your calculations, and assuming you can accurately predict all possible loading conditions and you know all the equations required. But it is doubtful you would end up with something more reliable than using the rules, even experts with lots of design resources occasionally create racing rigs that fail in unanticipated conditions.
     
  5. urisvan
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    urisvan Senior Member

    which design tables do you recommend? And which ones include formulas for multispreader rig?

    regards
    ulas
     
  6. urisvan
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    urisvan Senior Member

    hello PROS,
    waiting for reply.
    maybe i wrote it on the wrong category. The thread shold be placed on "sailing boats" section.
     
  7. Stumble
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    Stumble Senior Member

    Uris,

    I guess we are just trying to figure out why you want to design your own mast. Assuming the finished product will have anywhere close to 5 spreaders it is very complicated, and most mast manufacturers will throw in the design if you buy the stick from them. Since the expence of a large mast is pretty much in the materials and frieght I just can't imagine that doing it yourself would save any money.

    Secondly if you don't know where to get the formulas to design a narrow base cantilever then you likely haven't had enough engineering to apply them properly.


    That being said what you need to do is go get the textbooks for a engineering classes, particularly those specific to dealing with canitilever structures and start to study up on the science. Or call Buzz Bollinger wh could probably put a decent mast on your boat with all of 5 minutes of work.
     
  8. urisvan
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    urisvan Senior Member

    sorry,
    i am not trying to construct a mast for my vessel. i want to know how it is designed. I studied Naval architecture but they did not teach us to design the rigging at school and now i am asking to the pros in the forum. If they kindly share their method i will be very glad.
    Technically, I think the mast doesn't behave like a canitilever structure, especially the deck step ones. With its rigging, it is more like frame system. And i can solve the static of this frame system. BUt because the real worl is dynamic i guess there are some emprical methods based on experience and experiment. I want to know how this is done by a boat designer..

    regards
     
  9. Stumble
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    Stumble Senior Member

    Urisvan,

    Since you are more than just a crackpot (sorry for thinking that).

    My advice is to get intouch with a gentleman named Buzz Bollinger. He is a wiz at designing and specing rigs for everything from stripped down racers to more leizurely cruising boats. He is also normally more than willing to spend time speaking with anyone who is interested to learn more about rigs. I once took up over an hour of his time asking about some things completely irrelevent to his business model.

    I would also get a copy of The Complete Rigger's Apprentice by Brion Toss. It is an introductory text on rigging load calculations, as well as my go to reference for all things related to the rigging of boats. You can also get in touch with Brion at his website http://www.briontoss.com/spartalk/forumdisplay.php?f=1 Where there are a lot of professional riggers that toss around information and may be able to give you more technical information.
     
  10. Paul B

    Paul B Previous Member

    It will be easier to find him if you search under Ballenger.

    http://ballengerspars.com/


    Buzz is a good guy, but please keep in mind he has a business to run.
     
  11. Petros
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    Petros Senior Member

    If I did not use some standard rules this is how I, as a professional engineer would design a mast rig. It is not a cantilever, it is an indeterminate truss. You have to first define your boundary conditions, that is the wind forces both on the mast and rigging and on the sail. Since I have also had a lot of aerodynamics design experience I would try and develop a reasonably accurate (but conservative) pressure distribution on the sail and how it transfers to the mast.

    From this loading conditions you have to draw a Free Body Diagram of each component and determine every possible load combination on that might occur in all conditions of sail, pick the worst one as your design point. And than add a safety factor of at least 1.5 (if I was confident of my load conditions), or as large as 3.0 if I was uncertain of peak loads.

    Your shroud lines and back stay for example also add a lot of compression loads to the mast at full load conditions. this compression load will multiply the bending forces on the mass assembly in accordance with the Euler buckling formulas. The spreaders will have buckling and bending loads on them, and these transmit point loads into the mast as well. It is a complex combination of loads that are all interrelated. Not a simple design process but one of trial and error, with a number of iterations until you narrow down on a solution.

    That is why I would likely just use the design rules, unless I was building a very not standard rig.
     
  12. urisvan
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    urisvan Senior Member

    yes petros,
    you say that you can solve it as regarding that the problem is static and then multiply the solution with a safety factor.
    OR using desgin rules.
    I also appreciate design rules too. I think there is good experience and knowaledge at the backgroud of them.
    The question is WHICH design rules would you use and HOW can i obtain them?

    Regards
    Ulas
     
  13. fcfc
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    fcfc Senior Member

  14. urisvan
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    urisvan Senior Member

    yes i read this article.
    In a way(like in the book of Pierre Gutelle) it finds the forces that is applied to rigging by the sails.
    THEN it solves the system and calculates the loads of the rigging by Finite element analysis by taking these forces as external forces.

    regards
     

  15. yades
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    yades Senior Member

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