Validating your Sail boat design

Discussion in 'Sailboats' started by Projectnick, May 27, 2013.

  1. Projectnick
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    Projectnick Junior Member

    How do you go with validating your sailboat design. I do not see much material on validation techniques explained in detail beside just introduction. Sailboat design books just have brief intro on validation, but donot cover validation part in detail. By the way, I have a two meter boat on which i want to put sail. After i design a sail, how do i validate my design by simulation, provided that i am not going to build a sail, just design it. Any suggestion? any books?
     
  2. Eric Sponberg
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    Eric Sponberg Senior Member

    What do you mean by "validation"? Do you want someone to say it's OK? Do you want to know if it works the way you intend it? If you already have a boat, and you want to add a sail to it, and then want to "validate my design by simulation", the only way to do that is to create a 3-dimensional computer model of the hull and rig with sufficient detail and complexity to be accurate, and "sail" it in a Computational Fluid Dynamics program (CFD). That takes a lot of work, cost, and specialized talent to do all that for what would be a very small project of negligible overall importance.

    In short, there is no easy and cheap way to validate a design........except: Just go ahead a build the sail and stick it on the boat and sail it. That will validate it. Either it works or it doesn't, and if it doesn't work, you can study it, try different design features and settings, and try making it work. That is actually the cheapest, most accurate, and most direct way to validate your design. It's called full-scale testing.

    Just do it.

    I hope that helps. Good luck!

    Eric
     
  3. Skyak
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    Skyak Senior Member

    To validate

    1)work with customer to establish performance requirements and operating environment
    2)establish a plan to meet requirements -including performance models -customer approval
    3)prototype and test to conditions. If all conditions can not be tested and there will be an extrapolation as opposed to interpolation, the prototype will have to validate the modeling which will in turn run through all conditions.
    4)final validation is when you can prove statistically a sufficient probability of success (to a confidence level).

    Note: this is design validation ...there is also production process validation.

    If this seems like more than is commonly done it is because those designs were well within the established bounds of prior art.
     
  4. mgpedersen
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    mgpedersen Junior Member

    A lot of designers use a VPP to compare design against performance goals. They can compare against other known designs to see how it compares. The VPPs are essentially validated through race results, they are not as accurate as a towing tank but are close enough for most people and much more economical. You can also run several different designs to see which one looks to be most advantageous.
     
  5. PAR
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    PAR Yacht Designer/Builder

    I think what we're dealing with here is a person that has drawn up a design, but is now looking to have a designer or NA validate his decisions, by looking over the lines and plans.

    This is a fairly common request and with few exceptions, is usually turned away by the designer or NA. The reason is pretty simple, it costs just as much, if not a little more to examine and critique someone else work, as it is to generate a wholly new design from scratch. Once the prospective client gets a quote for the "validation", they don't call back.

    Projectnick has a model powerboat that he's attempting to put a sail pan on. I'll assume this is the desire for some sort of VPP or possibly more. He's said he's a NA student, but I suspect he's not very far along in his studies yet, based on previous posts and terminology employed within. Considering the very small size of the craft, I'd recommend some practical application to validate the design, such as an adjustable mast step and appendages, so you can move things around without having to rebuild the model. It's a model and this would be the easiest and fastest way to substantiate and validate the sail plan and appendages.
     
  6. Petros
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    Petros Senior Member

    That may be true PAR, but he did not ask for someone to validate his design, he ask how is a design validated. It appears he wants to learn how to do it himself, but can not find a reference in his texts.

    The term "validate" I think is troublesome, what does that mean? Anything at floats can be called boat, even a couple of logs lashed together. Put a mast and a piece of fabric on it (with some means of holding it open) and you have a sailboat. It many not perform well, but it will work. So what is the measure of performance that must be achieved in order for the design to be "valid"?

    I think Skyak got it correct; compare the customer's requirements against the results achieved. If it is small and inexpensive, than performance may be a secondary issue, design objectives were met. If it is performance over cost, than you have a different metric. Something more vague like "best performance for the money", than you have a difficult time defining your boundaries.
     
  7. Skyak
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    Skyak Senior Member

    'Validate' is a very well defined term in engineering. If you want to know how it is done look to the ASQ. I think you will find my description very concise.

    I think the conceptual problem here is that you can't conceive of doing all the work and you are trying to resolve the value of validation with the cost of validation -ie; wouldn't it just be better to put more money in into the product and less in validation? But this is just failing to document what is really going on which is validation based on prior art.

    NA's are treasure troves of prior art. That's why they crawl over failures and winners like flies on poop or potato salad, sopping up data. To some degree everything that comes from the NA's mouth or pen is based on prior art which is why we we flock to this blog for the valuable freebies. But to 'validate' a design justifiably costs a considerable amount and NA's are the only legally valid source for boats. If anything is lacking, I think it is the documentation of prior success. Boats that serve full lives without fail produce no documentation. In automotive, we had a significant budget for tearing down and analyzing product after a lifetime of use to justify our validation and correlate to our testing.

    There is another validation tool that is uniquely important to this case -the design failure mode effects analysis. The DFMEA is unique in that there is no human on the vessel in this case, so the failure is limited to the loss of the vessel plus damage to the environment. The low defined cost makes the development and prototype a closed loop that can be optimized.

    Projectnick is a student of NA. He has access to troves of data and experts. It appears that his assignment is confined to a tiny part of the task -ending with only a design. What I find disturbing is that he appears to be starting at 'design'. He can't figure out how to end because he didn't start at the beginning which is definition of intended function.
     
  8. Petros
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    Petros Senior Member

    that might be the fault of his curriculm. there is a disturbing trend in much of technical education where they start in the first year with a design project, and than follow up in the later years with the classes they needed to actually do the design. the objective is to keep the students interest with the creative part of the job, and it forces them to think though what they need to know to do the job. And they follow up with the necessary classes later, kind of keeping the first year design in mind to properly develop the design in later years. An interesting idea but I think a mistake, it only encourages careless design rather than teach fundamentals first (too "boring" for modern students), and than move on to design later.
     
  9. Skyak
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    Skyak Senior Member

    Oh I am sure it is the curriculum, but I think that it is wrong then to not give the info needed to produce 'the' answer. You put far more consideration into your projects that are just for your own enjoyment (and us to enjoy vicariously).

    It would be a great development project to do right. Give various aspects of the project to different students.

    By the way, what do you think of a 'robo-racing' class just for designers?
     
  10. tspeer
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    tspeer Senior Member

    I think this is a little misleading. A VPP is a program which estimates the performance. That estimate can be based on data from different sources. One can use the measurements from a modern rating rule and derive the coefficients that are used by a VPP to estimate the boat's performance. I think that's what you're talking about in your use of the term "VPP".

    The whole point of the tow tank is to provide data to feed a VPP to provide estimates of yacht performance. The tow tank itself doesn't tell you what the performance will be - it only tells you what the forces and moments are under the tested conditions. It's the VPP that puts the resistance & side force from the tank together with the rig aerodynamics and hull righting moment to estimate the performance.
     
  11. sharpii2
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    sharpii2 Senior Member

    My guess for the reason there is not much written about 'design validation', is because 'design validation' is part of the design process itself.

    The design process is a circular one, not a linear one.

    You don't go directly from concept, sketches, and calculations, to finished drawings.

    What really happens is you get an idea, you scale sketch it, then you check the preliminary math.

    In your case, you check for these five things:

    1.) is it going to have adequate displacement to support its weight without ridding too low in the water?,
    2.) is it going to adequate sail area(SA)?,
    3.)is it going to have adequate initial stability to carry this adequate sail area?
    4.) is the rig going to be strong enough to support this adequate sail area and survive a capsize?, and
    5.)is the boat going to have adequate ultimate stability?

    You may find yourself adjusting what you mean by 'adequate' for all five of these characteristics.

    You will almost certainly have to change your design idea many times, before you end up with something that is likely to work.

    For instance, you may start with a tall rig with generous SA and a deep, heavy bulb keel, to right it if it capsizes.

    But the rig is going to weigh something. And the taller it is the more its weight is going effect both initial and ultimate stability.

    So the bulb goes deeper and/or gains weight.

    The deeper bulb adds to ultimate stability, but subtracts from initial stability, as the keel's Center of Area (CA) is deeper.

    A heavier, shallower bulb subtracts from the boat's carrying capacity, so now you may need to make the rig shorter to get the bulb weight more in line. And this means less SA.

    I could go on and on.

    And that's what you're going to have to do to come up with a successful design concept.

    Then you have to figure out how it will be built.

    When you do that, you may find you might have to change a few things.

    This may put you back on square one.

    But each time you go around the circle, you will get closer to your goal, or you will find the goal itself may need to be 'adjusted'.

    But you will have to go around many times.

    Experienced designers are likely to go around the circle far fewer times for two reasons:

    1.) they have dealt with similar problems in the past, so have developed an 'eye' for what is likely to work and what isn't, and
    2.) They are scholars of boat design and have seen what many others have done successfully (and maybe not so successfully) and this too adds to their 'eye'.
     
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  12. Eric Sponberg
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    Eric Sponberg Senior Member

    Sharpii2's post is excellent, a nice summary of the design spiral. I would add that the method of construction is part and parcel of the design spiral up front and not necessarily a distinct and separate section when you get to the nitty gritty of doing the construction drawings. By that point, most of the structural elements will have been worked out by calculation and sketches so that the final construction drawings have minimal impact on the rest of the design.

    For example, let's say your designing a metal boat. It is going to have frames and internal structure, and generally you don't want that internal structure to impede on the accommodation. The structure will be hidden behind architectural panels and built-in furniture. So you need to make allowances for the space that the internal structure will occupy. You may not know precisely how deep the structure will be, but you make an allowance for it and design the interior accordingly. At some point, you'll do some calculations to determine how deep various elements need to be, and you may draw a few frames. Then you can adjust the architecture of the interior accordingly, and around and around you go.

    Another example is the bulkheads--the stiffeners are on only one side of the bulkhead, so the architectural furniture can be built more closely to the non-stiffened side of the bulkhead, but on the other side, it has to be offset by the depth of the stiffeners. So it's things like that that will work their way into the design as you go around the design spiral. Eventually, you get to the point where all the frames, bulkheads, girders, and details, etc. have to be drawn individually, and that is in itself a rather distinct part of the design process.

    Eric
     
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