Sail performance metrics

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

  1. Mike Inman
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    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
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    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
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    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
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    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
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    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
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    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
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    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
  8. rob denney
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    rob denney Senior Member

    If you are going to quote nebulous claims, please reference where they came from so we can add some context and know that you are not pulling them from your hat. "well known designer", "unstayed rig proponent" and "from my recollection" all suggest you are scared to reference the source as there is more to the discussion that you would rather we didn't know about.

    The unstayed masts I know of on larger boats that broke were for "reasons" like the Wylie Cat where holes were drilled for a spinnaker pole fitting. The mast broke at these holes. Of the stayed masts I know about that have broken, some of them had similar reasons. But by far the majority were caused by being set up incorrectly or by the failure of one of the many items that are required for a stayed rig, all of which are critical.

    The differences between stayed and unstayed masts are:

    1) it is not possible to set up a stayed mast incorrectly. There are no turnbuckles to buy and adjust, no wire stretch to allow for and no need to check it is in column. Drop it in the hole and forget about it until it needs repainting.
    2) There is little or nothing to maintain on an unstayed mast. No need to go aloft before a major voyage, no need to pull it for inspection every year, and no need to replace the rigging every 10 years.
    3) An amateur can easily build an unstayed carbon mast for less money than buying a stayed alloy one.
    4) An unstayed rig can be depowered on any point of sail. This is a huge safety feature, especially on multihulls and family cruisers.
    5) The main can be hoisted. lowered and reefed on any point of sail, in any wind strength.
    6) The boat can be much lighter built as the loads are all located around the mast and are easily diffused into the hull and deck. This also gives more scope for the interior layout.
    7) In a strong puff, the mast bends and depowers the sail. Automatically, and far more efficiently than a stayed rig. See the mast in the video at at 1.35 in 10 knots of breeze and 5.25 in 15 knots.
    8) There is no rigging for the wind to whistle through.
    9) They may not perform as well on a race boat, although given the comparative development money and hours, this is nebulous.
    10) Correctly engineered and built, a carbon mast will last longer than the boat. The "correctness" of the build can be checked before the mast leaves the factory. The fatigue loads mentioned by Sharpii are easy to engineer for. The "impact" of a sudden squall or a wind capsize is as much of a problem as a shroud breaking on a stayed rig in the same situation: negligible. It is far easier to design an unstayed mast than a stayed one. A wave capsize is more likely to break a stayed mast as there is no flex in the structure, assuming both are built to withstand the same heeling moment.
    11) Tight luffed headsails are not possible without temporary running stays, but other extras are.
     
  9. rob denney
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    rob denney Senior Member

    OOPs. A mistake in the above. Thanks Doug for pointing it out.

     
  10. CT249
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    CT249 Senior Member

    Okay.

    The "well known designer" was (EDIT) Lock Crowther. I'm not "scared" to reference that; it's just that I can't check up with Lock any more.

    You were the unstayed rig proponent. In a post on this forum (Oct 21 2016) you claimed that "30+ Wyliecats with unstayed rigs have been built over 25+ years....The only broken mast was due to a poorly installed, undesigned for, spinnaker fitting."

    This is incorrect. Both the Wyliecat 30 Uno and a 39 have broken rigs according to internet sources such as the 39's owner. There may be others. In other words, the claim was incorrect.

    I wasn't actually trying to highlight your inaccuracy; I was trying to make a wider point about the need for objective information. I like unstayed rigs and have used them a lot. However, saying that it would be better to have objective information (such as the percentage of a particular rig that fails, etc) would seem to be such an obvious thing that it is hard to see how anyone could object to it.
     
    Last edited: Dec 5, 2018
  11. rob denney
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    rob denney Senior Member

    "Objective information"?
    You partially quote something I said without referencing it, followed by a quote a designer (who never designed, built or sailed a boat with an unstayed mast) may or may not have said 30 years ago about unstayed alloy masts which were superceded by carbon masts 20 years ago.

    Neither is "objective" and barely qualify as "information".

    It may be objective to know the "percentage of rigs that fail", but if the reasons for them doing so are not known, the information is worthless. And if there was a problem causing the failures, and it has since been fixed, then the information is even less useful.

    The claim was about Wylie 30's, of which there have been 30+ built, and one mast fell down due to holes drilled in it for a fitting which it was not designed to take. This is explained in the thread you didn't reference. Why do people keep on claiming that sailors are conservative about rigs? https://www.boatdesign.net/threads/why-do-people-keep-on-claiming-that-sailors-are-conservative-about-rigs.56615/page-4#post-790351

    The other Wylie mast that may or may not have failed (I cannot find any references apart from an anonymous source on a defunct website which does not give any details of what happened) was on another design.

    As I also said on that thread, "It is not about which rigs stay up, it is about how much maintenance they require. Compare the failure numbers using boats which are 10+ years old, sailed regularly, have never had the mast removed for examination, have not replaced any standing rigging and have never had anyone up the mast to check for damage with an unstayed rig with similar use"

    Regardless, next time you quote me, please have the courtesy to use my name, reference the thread where I said it and, unless you are scared of being rebutted, let me know you are doing so. Thanks.
     
  12. CT249
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    CT249 Senior Member

    Rob, I was actually trying to be nice by not identifying you as the person who had made an incorrect claim about the number of Wyliecat failures, because your identity was beside the point that "actual facts such as statistical analysis of rigs lost as a percentage of boats afloat appear (s) to be missing" and that even the experts in certain rig types do not appear to know of all the failures of those rigs and their causes. I apologise if it upset you.

    However when it comes to etiquette, I note that you have quoted quite a few people in your posts. Did you (1) use their name all the time (2) reference the thread where they said it (3) let them know you were doing it? If not, why not? If you don't, why should others?

    My point was simply that it would be preferable if we had reliable numerical information about the number of rig failures and it's still hard to see how it can be said that is wrong.

    Surely no one would say it's better if we were ignorant of the number of rig failures. Surely there's enormous value in knowing how many failures occurred in any system, even if you don't know the cause. If people know that rigs (of any type) fail, then they can investigate the cause. If they don't know they are failing why would they look for a cause? If people are trying to determine what rig to get, then surely it's good to know how many are failing, and how well the experts know the failure rate and (if possible) the cause. We cannot say "type X rig is more reliable and only breaks because of reason Y" if we don't know how many rigs of that type have broken and why they did.

    I checked the earlier claim that only one Wyliecat rig failed and there was nothing that indicated that it was referring only to 30s. The reference to the Wyliecat 39 mast failure came from a post from someone who claimed to have owned the 39. They give their name on the site where I got the information from, Dolphin24.org - A Website For Dolphin Owners and Others Interested in this Classic Design http://www.dolphin24.org/zesty.html, and it fits in with the name of a 39 owner, as shown in race results. Therefore the information appears to be reliable.

    Actually, there was a third carbon Wyliecat mast that I know of breaking (C-Squared's stick in the 2004 Pacific Cup, pictured below) but I didn't mention it since there may have been construction errors.

    [​IMG]

    Actually, I think the Wyliecat 43/44 is one hell of a boat and it would be great to own. I am NOT saying that unstayed masts break more than stayed ones or anything like that. The point is that it would surely be better to have some information of the number of rigs of each type that fail than to not have the information.

    Finally, surely it's not "about how much maintenance they require"; that is merely one factor in choosing rigs and in assessing their reliability. If people choose an unstayed rig because they don't want to maintain stays, then good on them. If other people don't mind ringing up a rigger every few years then good on them too.
     
    Last edited: Dec 10, 2018
  13. Mike Inman
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    Mike Inman Junior Member

    I work in medical devices, we actively track our devices' performance in the field and seek customer feedback on problems.

    Still, it is widely estimated that for each reported complaint with a severity less than patient death, there are 10 similar events that go unreported.

    In other words, I wouldn't be surprised that a diligent effort to find references to broken masts finds only two, when there are 20 more similar cases out there not readily discoverable.
     
  14. Mike Inman
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    Mike Inman Junior Member

    This makes a nice tie-in (pun intended) to another post I made: Dux stays https://www.boatdesign.net/threads/dux-stays.61364/#post-844497

    With dux/dyneema type stays, how practical is it to self-inspect / replace the standing rigging without a crane and/or lots of time spent in a bosun's chair?
     

  15. CT249
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    CT249 Senior Member

    Interesting and very likely, Mike. At a guess as an Aussie I would also hear of more broken conventional rigs because that's what most of the boats that are in major ocean races use. We are more likely to hear of a boat losing a mast if it is doing a major race than if the same boat lost the same mast in the same place while cruising, because cruisers don't have PR coverage. We used to use many masts in the Hobart in the days of in-line spreader rigs, but these days the swept spreader rigs appear to be pretty reliable and losses (at least in local offshore racing) are much rarer.
     
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