Measuring junk sailing performance

  • 13 Jul 2017 13:44
    Reply # 4974389 on 4913961

    Edward,  off course I had you in mind, having much enjoyed all your reports.  All needed is to encourage others with different JR rigs to enter. 

  • 12 Jul 2017 12:24
    Reply # 4969891 on 4959160
    Deleted user
    Mark Thomasson wrote:

    I think the best way forward is to enter large open event, such as the RIOW, where there are standard boats of the same class.  The then gives a comparison of how the JR PY rating differs from the standard pointy rig.  With sufficient data this will give a method of establishing a comparison between JR rigs on different boats.  It would need the commitment to enter a few events to gain a good average.   If the JRA could provide some financial sponsorship, I would be in favour.  

    Hi, That is exactly what we have tried to do with Amiina and the last 5 RTIR, with some interesting stats.  coming out. 

    However to make further data available,   Amiina will be happy to participate in any performance measuring trials. 

    Amiina should be in the water most of the winter so we should be able to start collecting data fairly soon

  • 10 Jul 2017 13:31
    Reply # 4959160 on 4913961

    I agree with the earlier post, that a small dinghy or similar is no the best test bed.  It should be on the typical sort of yacht most members use, in the typical sea conditions, though this does make match racing two similar boats with different rigs too expensive.  

    I think the best way forward is to enter large open event, such as the RIOW, where there are standard boats of the same class.  The then gives a comparison of how the JR PY rating differs from the standard pointy rig.  With sufficient data this will give a method of establishing a comparison between JR rigs on different boats.  It would need the commitment to enter a few events to gain a good average.   If the JRA could provide some financial sponsorship, I would be in favour.  

  • 09 Jul 2017 16:07
    Reply # 4950623 on 4932940
    Anonymous
    Arne Kverneland wrote:

    Challenge number one is to find the right test boat, big enough to carry a real sail, big enough to be easily-handled by people over 60years or over 90kg. (Laser and Topper is too small). I have found a boat type which I think would suit the task: The PD Goose. There are some good clips of it on YouTube.

    I have just seen Michael Mangus' 15' trimaran on another thread about "Junk rig for 28' tri". I think this easy to build trimaran should also be considered if the two boat testing idea catches on because it is going to be a lot more stable and controllable than the PDGoose, and there already exists one with a split junk rig!

    I find this a much more usable proposition than the PDGoose for two boat comparisons, as it will be less dependent on helmsman's weight and fitness.

    See the build process here

    https://www.youtube.com/watch?v=bP4wwV9XPOo

    and sailing here

    https://www.youtube.com/watch?v=cANXDLV2tJM

    The total cost was around Euro 1100 and about 110 hrs build time. The Bermudan rigged version uses a Sunfish sail, which is 6.9m2, but the sailing videos suggest the trimaran could carry a slightly bigger sail.

    Anyway, food for thought, and a clue as to the budget.


  • 09 Jul 2017 12:24
    Reply # 4949832 on 4945123
    Anonymous
    Bryan Tuffnell wrote:
      Any decent wind tunnel allows pitch, roll, yaw, heave, surge, sway, AoA and velocity changes, including rate changes; that's their role. Dynamic testing in a tunnel is intended to give results whereby the variables are reproducible, controllable and quantified, free from the noise and scatter that plagues 'real world' testing in an unstable environment. 

    Most engineering universities seem to have a suitable tunnel, and there's usually enough students looking for a project to generate more help than is needed! I've never paid for tunnel time, even when using one for commercial purposes.

    Hi Bryan,

    You make a very interesting suggestion. You clearly have the experience to supervise such a project. Would you be willing to take it on, i.e. to supervise the student(s)?

    I was of the opinion that renting a wind tunnel would be prohibitively expensive, but if we can persuade a student to do it for us as part of their degree project, then it potentially becomes very economical.

    Although the points raised by David & Slieve about real world conditions are very valid, it would still be very interesting to have well documented lift and drag curves from zero to stall for the various rigs developed since Joddy Chapman's MSc. I think that would not need an MSC student but would be suitable for an undergraduate final year project to test, for example, a flat junk, a cambered panel junk, a bendy and/or hinged batten junk, a split rig junk, an aerojunk, and a wingsail junk, i.e. up to 7 different types, and possibly more. The tunnel needs to be as big as possible to minimise the scaling issues.

    Even stable airflow tests would be worth doing, although if we can get dynamic testing as well, so much the better. Making these undergraduate projects will lead to shorter reports! As we have seen, MSc's create meatier tomes than we really want.

    Naturally I think a wind tunnel programme should happen in parallel with real world instrumented testing as originally proposed, especially if it is effectively free, as Bryan suggests it should be.


  • 09 Jul 2017 10:29
    Reply # 4949776 on 4913961

    Interesting, Bryan, so maybe things have changed in recent years. My initial approach was to find MSc students looking for a project but if I remember correctly they could only offer small cross-section tunnels and I would have had to make the models for them. That's fine for small foil shapes made of tin, but I felt that it would need a large cross-section tunnel to accommodate even a scaled down full rig made of a soft flexible material, which is a bit more daunting. That's where it got out of hand, and beyond the range of my pocket.

    Anyway, I settled for the more fun approach of the odd handicap race and am very happy with the information gained.  

    Cheers, Slieve.


  • 08 Jul 2017 23:15
    Reply # 4945123 on 4938306
    Deleted user
    Slieve McGalliard wrote:

    Hi Bryan,

    I don't know where you can get a large cross section wind tunnel very cheaply as it wasn't available when I researched that avenue some 10+ years ago. A tunnel may give accurate measurements, but they would be useless for comparing rigs as they would be static results, and small junk rigged boats are anything but static. It would be necessary to include dynamic performance with stall recovery an important consideration to be of any use.


    Hi Slieve (and David)

    Any decent wind tunnel allows pitch, roll, yaw, heave, surge, sway, AoA and velocity changes, including rate changes; that's their role. Dynamic testing in a tunnel is intended to give results whereby the variables are reproducible, controllable and quantified, free from the noise and scatter that plagues 'real world' testing in an unstable environment. 

    Most engineering universities seem to have a suitable tunnel, and there's usually enough students looking for a project to generate more help than is needed! I've never paid for tunnel time, even when using one for commercial purposes.

    I won't labour the point any further.

  • 08 Jul 2017 16:12
    Reply # 4938554 on 4935920
    Anonymous member (Administrator)
    Scott Dufour wrote:

    Anyway, I'm in favor of both approaches.  For those who like to tinker and experiment, by all means, make some cool direct comparisons.  And also, why not just gather data on what's out there already?   Financially, the equipment is cheap, and protocol training could be straightforward.  Expenses for the actual data gathering would be born by the individuals - we are a volunteer organization. 

    To this end,    David and I are offering KRKA for testing should the committee decide to go ahead with Alan's idea.    We have hinged battens which makes KRKA of possible interest.

    If we are going to produce meaningful data,  I guess all the different forms of the rig need to be evaluated.

    Lynda

  • 08 Jul 2017 11:59
    Reply # 4938306 on 4913961

    Hi Bryan,

    I don't know where you can get a large cross section wind tunnel very cheaply as it wasn't available when I researched that avenue some 10+ years ago. A tunnel may give accurate measurements, but they would be useless for comparing rigs as they would be static results, and small junk rigged boats are anything but static. It would be necessary to include dynamic performance with stall recovery an important consideration to be of any use.

    Unless the measurements are taken in the same sea state at the same time they will be of little use, so you always come back to direct boat on boat tests. There is really no way to ensure that tests repeated even on the same rig/ boat combination on different days will produce consistent usable results, which would be usefully compared with other rigs measured elsewhere

    Cheers, Slieve.


  • 07 Jul 2017 17:31
    Reply # 4937359 on 4936364
    Bryan Tuffnell wrote:Scott, I agree with you. It does seem to me that 'measuring junk sailing performance' by either approach is likely to prove to be an expensive way of coming face-to-face with the challenges of variables and noise. 

    If the goal was changed to 'measuring the performance of various types of junk rigs' it would allow the use of tunnel testing, and it suddenly becomes very cheap, very easy, and very accurate.

    I'm all for reducing variables, but tunnel testing reduces them too far. In the real world, we'd like to know about such things as which rig is better at powering a boat upwind against a short chop, which may not be the same as which rig is better in flat water. Pitch and roll are going to make an appreciable difference to performance.
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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