Sail performance metrics

Discussion in 'Hydrodynamics and Aerodynamics' started by misanthropicexplore, Jul 25, 2018.

  1. Mike Inman
    Joined: Oct 2018
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    Location: Jacksonville, Florida

    Mike Inman Junior Member

    Absolutely true. There is, however, some very basic physics involved which can demonstrate that: for two mast-like structures constructed of the same material and of equal strength, a hollow one will be lighter. This is true when comparing solid tubes to pipes, and the physics continues to work as you spread load handling out further from the central axis as with stays. It's the reason that huge radio towers are (usually) built with guy wires.

    In the sailboat application, there are compromises where the more massive unstayed mast presents advantages unrelated to just standing up straight and taking the load of the sails, but an appropriately designed/implemented unstayed mast will always be heavier than an appropriately designed/implemented stayed mast - that's unavoidable physics/material science.

    Now, as to what's practical in the real world - that gets into all kinds of economies of scale, market availability, etc. which ultimately ends up becoming a personal choice as to where you want to live on the cost/benefit curve and what your personal valuation of the tradeoffs are.

    Only if you (and/or your insurance company) want to be reasonably sure of the outcome. Jeff Foxworthy's Redneck's famous last words: "buckle up, I'm gonna try somethin'."
     
  2. DCockey
    Joined: Oct 2009
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    Location: Midcoast Maine

    DCockey Senior Member

    A stayed rig has numerous components, each of which is critical to the mast staying upright. In contrast an unstayed mast has only one critical component, the mast itself. So in general a stayed rig has more potential failure modes than an unstayed mast, and more components to inspect and maintain.
     
    rwatson likes this.
  3. Mike Inman
    Joined: Oct 2018
    Posts: 48
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    Location: Jacksonville, Florida

    Mike Inman Junior Member

    Absolutely true, tradeoffs. More mass aloft: bad. Less complexity aloft: good, potentially very good in lots of ways. Better than a lighter (most likely less expensive) rig? Depends on your values.

    In another thread, I asked about Dux stays - lighter than steel - potentially stronger than steel for lower weight, more easily worked and installed with simple tools, also subject to chafing and UV exposure failure modes that steel is not, but more readily inspected than steel which has some "surprise" hidden failure modes. Replacement Dux stays are much more easily stowed onboard and installed while offshore. Do the advantages outweigh the disadvantages? Depends on your values.
     
  4. CT249
    Joined: May 2003
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    Location: Sydney Australia

    CT249 Senior Member

    So what do you propose people do? Just say "oh, this guy who wants to sell me his mast MUST be the first person in world history to be all-wise, all-knowing and utterly unbiased so I have to accept every single thing they say without checking on it"? Why is that better than doing some research that will indicate whether the person talking masts has done their homework? For that matter, why must I believe you when you say you know what the only guarantee is? And as for your "FFS" crap, GMT and others will sell you a mast. People who sell things are vendors. Some of them, like Forte, offer laminate design and stress analysis.

    Of course, you could take the Roger Taylor approach, shared by some member of the JRA, and buy a light post and fit it yourself, with apparently no designer input. Why is that approach good enough for Roger but not for others?
     
    Last edited: Nov 7, 2018
  5. CT249
    Joined: May 2003
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    Location: Sydney Australia

    CT249 Senior Member

    Yep, very true. And there's also human psychology, which means that vendors of any type of rig are normally going to be subconsciously biased towards their type.
     
  6. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Please dont substitute my words " a qualified person" for "this guy .... all-wise, all-knowing and utterly unbiased"

    The only "research" you can do is getting an engineering certificate that an insurance company will accept, and a copy of the calculations.
    It's good enough for 120 story buildings and 130,000 tonne ships - but not for you ?

    I can say that it IS the only guarantee because there is NO OTHER USEFUL METHOD ! How is your informal survey going ?

    Don't kid yourself. They won't sell you one that would come back on their reputation, - there are consumer and civil laws.

    "A mast to suit your requirements
    GMT has engineered, detailed and built masts for an unlimited range of vessels and types of sailing. Whether you own a heavy displacement megayacht, traditional or modern cruiser, a classic yacht requiring a replacement spar in refit or a round-the-world race boat, GMT has the experience and successful record you can rely on. We have built masts from 30 to 140 feet (10 to over 40 meters) in length. ....The choice depends upon your individual requirements, and we will discuss the optimum solution with you when we hear about your requirements."

    You are JOKING Right ????
     

  7. CT249
    Joined: May 2003
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    Location: Sydney Australia

    CT249 Senior Member

    The point about qualifications is that you don't have to accept everything a qualified person says, especially since there are qualified people on both sides of the stayed/unstayed issue. There were also qualified people involved in designing rigging years ago, when up to 10 masts could drop in a single race. There are qualified people who are designing bulb keels that fall off and kill people. Qualified people are not perfect people, therefore it is reasonable to try to obtain some sort of information about how accurate their claims. Asking for more information so that their claims can be checked is just reasonable homework.

    An insurance company will also ensure a fairly fragile, leading-edge racing rig that depends on runners, therefore the fact that an insurance company will accept a certain rig is not proof that it is more reliable than a different type of rig.

    No, I'm not joking about the Roger Taylor approach. What's wrong with the approach that has worked for all the miles he's done? It may not be optimal but it seems to have worked.

    I didn't say Forte etc would sell anyone a mast that would "come back on their reputation" and I have no idea why you thought that. The website says that they will sell you one they engineer to the optimum solution. I assume Ted Van Dusen and others will also be happy to take your money if you ring up and say "Hi, I have some money and want a mast. Here is a copy of the hull design." They are selling the masts, therefore they are vendors.
     
    Last edited: Nov 8, 2018
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