Measuring junk sailing performance

  • 29 Jun 2017 08:17
    Reply # 4923407 on 4922225
    Alan Boswell wrote:

    Annie suggested I should email the people who have developed different versions of the rig, which I will do if I can track them down, but I don't necessarily know about all that is happening, so it would be very helpful if anyone developing rigs would put a post on this forum to let us know what they are doing, or have done, and if they would be interested in doing some testing to get performance data for their rig and boat combination.

    OK, I'll volunteer.

    I now have a rig that is very easy to work with, it reefs and furls well, tacks and gybes well and goes to windward quite well enough for cruising purposes. How well? I don't know.

    Yet I still hanker after the wingsails that I was trying to develop on Tystie. Were they faster to windward? I felt they were, but had no proof. The character of the airflow, as revealed by a wind-wand, was very good. I failed to get the engineering good enough, but they were very easy to sail with, once rigged, and I was convinced that the future of sailing lay somewhere in this direction (the people at Beneteau thought so, too, but I've heard nothing recently about their wingsail trials).

    Now I have a boat for which a wingsail would be a more achievable proposition, at a smaller size than was the case with Tystie. I could make a wingsail this coming winter, to the same planform as my current sail. I have enough cloth for the sail, and could reuse most of the hinged battens that are in the current sail. I think this would be a worthwhile comparison - same area, same planform, same camber, but one sail with a sharp leading edge and exposed, draggy mast, the other with a better foil section, a rounded leading edge and a concealed mast.

    But I would need a self-contained wind and water sensor setup, at either end of a long tube that I could lash to the bow. Anyway, I've always felt that masthead anemometers are not much use in a seaway, when the masthead is describing wild circles.

  • 29 Jun 2017 01:18
    Reply # 4923122 on 4923065
    Deleted user
    Annie Hill wrote:
    Bryan Tuffnell wrote:An alternative may be to produce scaled models of the rigs, and trot them along to the nearest university that has a wind tunnel. It's easy to derive the relative magnitudes and directions of lift and drag at different angles to the wind, and that may be as far as anyone needed to go.
    Been there, done it.  Read all about it here.  Well, not exactly - there weren't as many experimental rigs to play with, then and rather than making comparisons, we were trying to understand how junk sails to their stuff. 

    Interesting, but the comparisons are what's needed in this case.

    I belong in the camp that wouldn't use windward speed potential as the criterion for selecting a rig, and personally wouldn't spend a lot of money on determining which rig was 'the greatest', simply because for me there are too many other factors in that choice. Like most of us though I have an idle curiosity in seeing which rig is fastest. 

    In a previous life, I've used instrumentation and software to try and determine aircraft performance, often in conjunction with side-by-side in-flight comparisons. I've done a fair bit of it, and always found it very hard to get results that are trustworthy unless there's a clear-cut winner, and that's using $big$, laboratory calibrated instruments. It's really hard to do. 

    I'm just suggesting tunnel testing of models is a way of getting qualitative results at low cost, with fewer variables, than instrumenting full-scale boats. It's just less fun than hooning around a bay in a sailboat.


  • 28 Jun 2017 23:29
    Reply # 4923065 on 4922883
    Bryan Tuffnell wrote:An alternative may be to produce scaled models of the rigs, and trot them along to the nearest university that has a wind tunnel. It's easy to derive the relative magnitudes and directions of lift and drag at different angles to the wind, and that may be as far as anyone needed to go.
    Been there, done it.  Read all about it here.  Well, not exactly - there weren't as many experimental rigs to play with, then and rather than making comparisons, we were trying to understand how junk sails to their stuff.  But the net result (of a PhD) was 'Erm, well, yes, it does work, but I'm not quite sure why.'  Back to the drawing board, or in this case, the amateur junk riggers.

    But keep at it, junkies.  Knowledge, as they say, is power and there are still some people who want more power to windward.


  • 28 Jun 2017 21:54
    Reply # 4922883 on 4913961
    Deleted user
    An alternative may be to produce scaled models of the rigs, and trot them along to the nearest university that has a wind tunnel. It's easy to derive the relative magnitudes and directions of lift and drag at different angles to the wind, and that may be as far as anyone needed to go.

    If someone wanted to convert those values to boat speed and pointing ability, a little more data on the hull would be required. However, that data would also be easily acquired, and easily modified to allow for different hull types, and the maths isn't hard. 

    Orville Wright managed to make meaningful comparisons with models mounted to the handlebars of his bicycle. With a few simple caveats, such as the effects of heel angle, pitching and scaling, modeling may provide very good relative results...

    ...at a cost of some of the magic of innocence, perhaps?

    Last modified: 28 Jun 2017 21:55 | Deleted user
  • 28 Jun 2017 17:06
    Reply # 4922225 on 4913961
    Anonymous member (Administrator)

    My thanks to Slieve & Chris for pointing me at more useful websites. All assistance gratefully received.

    Maybe I missed it, Slieve, but have you published performance data for the split junk? I note your suggestions for making the necessary instruments. You clearly have the expertise. Are you volunteering to make them? I have neither the skill or the inclination to do that.

    Would it not help if you were presented with a package of instrumentation, logger, and analysis software at no cost to yourself plus some assistance in setting up and running the tests? I would have been delighted if it had been available to me when developing the SwingWing, or even for comparing the performance of the sloop and schooner versions of the Sunbird 32, and bendy battens versus stiff ones. All of those would have been useful to members of the JRA.

    Interestingly, it seems there are various analysis packages out there which are free or very low cost, and it seems the logging function can often be done by a phone, tablet, or laptop, so it may be we are only looking at the cost of the instruments. Chris's Airmar weather station with cable costs around £800 according to their website, and we can get a set of wireless wind instruments and a log from Raymarine for about the same amount.

    Annie suggested I should email the people who have developed different versions of the rig, which I will do if I can track them down, but I don't necessarily know about all that is happening, so it would be very helpful if anyone developing rigs would put a post on this forum to let us know what they are doing, or have done, and if they would be interested in doing some testing to get performance data for their rig and boat combination.

  • 28 Jun 2017 15:26
    Reply # 4921936 on 4913961

    Some questions must include – how much would the membership of the JRA gain from the various experiments or measurements? How many members would even understand let alone gain benefit from the effort? I'm not talking down to the members here but simply recognising that most members want to enjoy the advantages of the rig but may not be too bothered about the full technical elements. As there are so few actually experimenting with new rigs I question that there would be any significant gain from potentially significant expenditure. Although I have a formal technical background I cannot see any return on any funds spent this way. Is it not up to any member how has this interest to fund it themselves, cheaply as discussed below, just as those of us who risked our own funds building experimental rigs paid for experience out of our own pockets? I have yet to make any financial gain from the split rig, nor do I seek it, and no-one sponsored it for me.

    The racing is largely non technical, involves little extra expense (apart from entry fees which hurt) and is a bit of fun that everyone can understand, and gives a target to aim for. Data plotting would not have to be expensive in this computing age and could be easily be achieved by the few who would be interested (and possibly cost them less than the race entry fees we have paid).

    All that is required is the measurement of 1) boat speed through the water, 2) relative wind speed and 3) relative wind direction. Feed these three parameters through a suitable interface, possibly even a cheap Raspberry Pi, into a laptop computer/ tablet, and use the available (free?) software to log and produce polar diagrams. All three parameters can easily be obtained from simple DIY devices so money does not necessarily have to be spent on expensive commercial units.

    Boat speed could be taken from a simple trailed log, even with a home made propeller made from 15 mm copper pipe with the aid of a mitre block made of wood with 3 nails, and fitted with a wooden or plastic nose cone (as I have done in the past). The boat end only needs a bicycle wheel hub and a bike speedometer or a alternatively a reed relay or field effect transistor. Total cost for materials could be around £10, the log line being a significant part of it!

    The wind speed/ direction could be a unit fitted to a boat hook mounted vertically above the pulpit for windward measurements, and to the pushpit for broad reaching and running measurements.

    In the 50s/60s our model flying club had an anemometer made from 3 half table tennis balls and a small geared DC motor (Mighty Midget) feeding a sensitive voltmeter. Calibrated from a slowly moving car in calm conditions, it worked well. A modern version could use reed relay, bicycle speedometer or hall effect transistor to feed directly into the interface. Again we're talking pennies.

    The wind direction would be the most complicated requiring either a 360° potentiometer, which would suffer from friction and wear, or a synchro, or a multi element light sensitive diode setup, to get the required sensitivity, all of which is not impossible. A magnetometer system might also be made to work, though dip angle and healing would undoubtedly produce significant errors. Again the work is not beyond the realms of human possibility, nor the frugal pocket.

    This was a route I had considered even though Poppy came with full racing instruments, and with present day computing convenience I would now take the NMEA signal stream straight to a computer. Still, the racing way has produced the most interest for the general membership, the most publicity for the rig and fun for the participants.

    Edward and I did fit a spring balance water-speed device to Amiina, but it was more fun just to try to sail the boat well. The expanded scale relative wind direction of the VMG meter was the most useful instrument on Poppy and was a great help in keeping her within the 'groove'. That is the most important information for close hauled sailing, and where a good wind vane steering gear is so good, as Bunny Smith knew. Edward and I must get that project back in action again soon.

    On a slightly different tack (pun intended), in the first Island Race in Amiina we were 5+ hours into the race at the east end of the island and sailing rather badly (sails stalled) into a horrible choppy sea churned up by the many boats about us. The chop was simply stopping the light weight boat with stalled sails and it was awful, when a beautiful bow came slicing into my peripheral vision. It was a FolkBoat pointing higher than we were and going like a train, as if the water was as flat as a mill pond. Beautifully sailed, it was impressive and made us wake up a little, but the interesting point was that it had started the race some time earlier than we had and was handicapped as faster (which it should be) so we were actually miles ahead of it in race position. The point of this is that sea state and crew alertness have such a big effect on the instantaneous performance that I believe it would be difficult to get useful information from data logging and polar plots. Surely it is more important to get out there and turn heads. With a good rig you get very funny looks when you  overtake a boat which is flying a cruising chute. They don't like it!

    Ten minutes on Google produced the following web sites which may be a start for those interested in cost effective instrumentation.

    http://www.yachtingworld.com/features/5-tips-developing-polar-diagrams-optimise-speed-71464

    http://www.ybw.com/forums/showthread.php?423190-Polar-diagram

    http://www.plaisance-pratique.com/polauto-mesurer-la-polaire-reelle?lang=fr

    http://www.instructables.com/id/DIY-Anemometer-and-Windvane-for-Standalone-Weather/

    Cheers, Slieve.

    P.S. In answer to Arne's comments on racing boats, which I fully agree with, given unlimited funds my ideal small boat would be, wait for it, a FolkBoat fitted with a split junk rig. (Who said Jester?) I'm sure that that would turn heads.


    Last modified: 28 Jun 2017 15:50 | Anonymous member
  • 28 Jun 2017 13:07
    Reply # 4921727 on 4913961
    Anonymous

    Some of the more geeky among us enjoy an occasional bit of complexity. I have fitted one of these (Airmar PB150) to the mast head of China Girl.

    It produces a serial stream of values for the following parameters:

    Lat, Long, Speed over ground, Course over ground, True and magnetic heading, True and apparent wind speed and direction, Air temperature & wind chill, barometric pressure.

    With a digital log derived parameters such as leeway can be obtained.

    All completely unnecessary, of course, but giving the potential for lots of geeky fun, and providing the kind of data Alan is talking about. Configured to log every minute or so, more than sufficient statistically significant data can soon be obtained to produce polar plots for a given boat/rig in various wind strengths and sea states.

    I plan to delay fitting my new split sail until I have such data from the old one with which to compare.

    Instruments such as the above produce data as a comma-delimited serial stream suitable for the RS232/COM port of a laptop computer. The format of these serial data is often that specified by the NMEA 0183 or similar - see that for nav data (identified by the string $GPGGA) below, giving time (17:28.14 UT) latitude (37 23.46 N) and longitude (122 02.26 W).

    $GPGGA,172814.0,3723.46587704,N,12202.26957864,W,

    2,6,1.2,18.893,M,-25.669,M,2.0,0031*4F

    Last modified: 28 Jun 2017 13:10 | Anonymous
  • 28 Jun 2017 12:24
    Reply # 4921669 on 4913961
    Anonymous member (Administrator)

    NMEA 0183 and NMEA 2000 are internationally agreed "languages" that allow instruments to talk to each other and share data, so that, for example, a wind instrument can take boat speed data from the log and calculate and display the true wind speed and angle. The 2000 version superceded the 0183 version, but both are still in use.

    The equipment we would need falls into three "packages".

    1/ Instruments, to measure wind speed and direction, boat speed, and ideally gps as well. If they are already on the boat we could use NMEA connections to get the data to record it, but that raises other issues of calibration, so having a set of wind instruments that can be moved from boat to boat is probably going to be the best solution. Raymarine sell a wireless set of wind sensors and a display instrument which would do the job. Probably more boats have a log, and that is perhaps more difficult to move from boat to boat, although Raymarine do a transom mounted one, or we could perhaps put a hull mounted one at the bottom of a pole as per the yachting mags. GPS is quite widely available in phones and tablets, but is not essential. It is useful for checking the calibration of the other instruments.

    2/ A data logger:- a memory device that will record millions of data points for later analysis. This can be any computer with a good enough spec, provided we have the necessary cables or wireless system to connect the instruments to the computer. There is an off-the-shelf box that will do this and reduce the messing about trying to make things work. It is small enough to ship around the world by post or courier.

    3/ Software:- to take the millions of data points collected and turn them into some useful information. Again any computer with an adequate spec can be used for this, but setting up the software will take time and effort, so it would probably be best to only use a few different computers. The data files can be stored and shared over the internet.

    The point of the project would be to collect data that would be available to all members, and to give us solid data about the performance of various rigs and boats that might help us to chose the best rig for our type of sailing, and to get the best performance out of whichever rig we choose.  I have no problem with seat of the pants sailing - I do it a lot - but I do have a problem with discussing the merits of different rigs when we have no reliable information about what their performance actually is, only anecdotal reports.

    The proposal is coming along, and researching the different systems available is proving interesting, but I don't yet have all the answers I want.


  • 28 Jun 2017 10:37
    Reply # 4921571 on 4913961
    Anonymous member (Administrator)

    I am not so sure it is such a good idea to choose one of these light runners, like Albin Express, X-79 or X-99 for racing with a junkrig, and this for two reasons:

    ·         These boats are already really generously rigged, and with very tuneable sails.

    ·         They are light and beamy, with low ballast ratio, so for upwind performance  in some wind, they rely on piling lots of moveable meat on the weather rail.

    Fitting a JR to these boats will in most cases mean de-tuning them, so the originals will by and large beat the JR version on elapsed time.

    When I was searching for the next boat after Frøken Sørensen, there was an X-79 on the market, nearby. It would no doubt sail well with a JR and be faster than the IF I eventually bought. Still, compared to other well-handled X-79s, she would not shine. The IF on the other hand is moderately rigged, so Ingeborg’s JR, which happens to have the same area as mainsail plus Genoa 1 on the original IF, should stand a better chance. Moreover, her narrow beam and 58%(!) ballast ratio does away with any need for sitting out to keep her upright. She is probably faster the lighter the crew is.

    Back to Alan’s original theme of measuring the performance with instruments: Even America’s Cup and Volvo Ocean Race teams do not rely on instruments and polar diagrams alone: They have sister boats to match race against and test every change they do to sails and rigging by match-racing. Polar diagrams are fine to show as sales arguments in brochures, but they are simply not accurate enough for getting out the last 0.5% racing speed.

    For my own part, I just use my eyes and see how my boats compare.

    One final thing: I tend to raise and drop the sail very close to the harbour. This lets people there watch her sailing at full speed on short distance. I regularly get comments on how fast my boats are. Stavanger junks surely have no local reputation for being slow.

    Arne


    Last modified: 14 Oct 2019 20:27 | Anonymous member (Administrator)
  • 28 Jun 2017 10:05
    Reply # 4921559 on 4913961

    I echo Annie's comments re existing instrumentation. I have a good GPS because I rather like to know where I am. I have no log or wind instruments, because I don't need them for cruising, input from my mk 1 human eyeball and mk 1 seat of pants gives me all the data I need. 

    Any instrumentation package would need to be self-contained, just add 12V power and switch on. Wasn't the YM boat test kit like this, just needing to be strapped to the pulpit?

       " ...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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