Measuring junk sailing performance

  • 07 Jun 2019 09:30
    Reply # 7563162 on 4913961

    Here are the Polauto plots for Weaverbird's runs yesterday.

    What I think I'm seeing is that Amiina's best VMG is at 36˚ AWA on port tack and 32˚ AWA on starboard tack. Edward tells me that there is a sharp fall-off in performance if he heads too high and the jiblets flutter - the boat has to be kept "in the groove". That would appear to be borne out by the fact there are no results showing at less than 36˚ AWA on port tack. Amiina seems to have starboard as her "best tack". That would be with the mast to windward of the mainsail's luff, giving better airflow on the lee side.

    The plots for Weaverbird are showing that I didn't really get enough data at the close reaching angles. I got plenty of data when close hauled, though, and it appears that I get best VMG at 32˚ AWA under full sail on both tacks (run 1 P & S) and 36˚ AWA with one reef on both tacks (run 2 P & S). Yesterday was quite breezy, and I was just able to hold onto full sail for run 1 and took a reef for run 2. I get the feeling that the "groove" when sailing to windward is quite wide - there is a wide band of AWA in which she sails well, or high tolerance to varying angles of incidence of wind on the sail. This is what I had hoped and expected to find, as a feature of the rounded luff. of the wing sail.

    This is quite encouraging. David Harding, who has done more boat tests than I've had hot dinners, reckons to see 32˚ AWA as giving the best performance on bermudan rigged boats. However, this would be measured by a masthead wind sensor, which may well be giving a different reading from our wind sensor out on the boat's quarter.

    And perhaps I was right when I was observing a difference in pointing angles of 3˚- 5˚ : 32˚ vs 36˚!

    4 files
  • 06 Jun 2019 16:58
    Reply # 7559805 on 4913961

    Alan has now run the data for Amiina through Polauto, and the results are attached.

    3 files
  • 06 Jun 2019 16:54
    Reply # 7559787 on 7557304
    David wrote:

    Weaverbird is in Poole Harbour, and this morning we managed a few runs on Amiina with the performance measuring equipment rigged. The data is yet to be processed. 

    This afternoon, we sailed Weaverbird (wing sail) and Amiina (split junk) together, assessing relative pointing angles and speed. On all points of sail, our speeds were equal. Amiina is a little shorter, so Weaverbird should have been faster by about 3.5%, but since Weaverbird cannot raise the outboard whereas Amiina can, and Weaverbird has twin keels whereas Amiina has a fin keel, I think this would account for it.

    However, the noticeable difference was that Weaverbird was able to point appreciably higher, by about 3 -5 degrees, while sailing as fast.

    Edward disagrees, says the pointing difference was 2 - 2.5 degrees!

    I did two runs on each tack on Weaverbird this morning. CSV files for both boats are attached.

    7 files
  • 06 Jun 2019 16:21
    Reply # 7559710 on 7559040
    Anonymous wrote:

    David, if you are pointing that much higher, whilst dragging an outboard, it says a lot for the latest rig.  Look forward to seeing the full stats, speed and tacking angle.

    well done.

    I agree. For an analyst very exciting stuff. Data from Amiina/split junk and Weaverbird/wing-sail...head-to-head. I look forward to downloading and processing the CSV files.

    robert self 

    Last modified: 06 Jun 2019 16:24 | Anonymous member
  • 06 Jun 2019 10:21
    Reply # 7559040 on 4913961

    David, if you are pointing that much higher, whilst dragging an outboard, it says a lot for the latest rig.  Look forward to seeing the full stats, speed and tacking angle.

    well done.

  • 05 Jun 2019 17:16
    Reply # 7557304 on 4913961

    Weaverbird is in Poole Harbour, and this morning we managed a few runs on Amiina with the performance measuring equipment rigged. The data is yet to be processed. 

    This afternoon, we sailed Weaverbird (wing sail) and Amiina (split junk) together, assessing relative pointing angles and speed. On all points of sail, our speeds were equal. Amiina is a little shorter, so Weaverbird should have been faster by about 3.5%, but since Weaverbird cannot raise the outboard whereas Amiina can, and Weaverbird has twin keels whereas Amiina has a fin keel, I think this would account for it.

    However, the noticeable difference was that Weaverbird was able to point appreciably higher, by about 3 -5 degrees, while sailing as fast.

    David Harding, the photographer and boat tester who submits articles to PBO, YM and YW magazines, was with us in his RIB for both sessions, and there just might be an article appearing in one of the magazines in due course. He was very interested in both the performance measuring kit and the wing sail.

  • 08 May 2019 13:05
    Reply # 7329225 on 4913961

    Hi David, her mooring is on the Plym just off Oreston but she will not be there till late summer.


    Mark

  • 07 May 2019 08:39
    Reply # 7326633 on 4913961

    Thanks for volunteering, Mark. Whereabouts in Plymouth is Stalemate based? I'll be coming into Plymouth Yacht Haven at some stage, to visit relatives who live nearby.

  • 06 May 2019 12:16
    Reply # 7324645 on 4913961

    Hi,

    David Tyler wrote

    Who else? Boats that have a major rig upgrade in the offing are prime candidates, so that we can carry out "before and after" tests to see what difference the upgrade has made. Boats with new and unusual rigs are also candidates - Blossom, for example. But we also need to test mainstream flat sail, cambered panel and hinged batten rigs, to build up our base of knowledge, and to be able to compare them with such rigs as split rigs, aero junks, wing sails etc. Those of us who develop and improve our rigs should really be in possession of cost/benefit data - after spending more time, money and effort in trying to make a better rig, was it worthwhile? How much better, at how much extra cost? That's what we'd like to find out.

    I am just fitting a new flat sail to Stalemate (Westerly Konsort Bilge keel) for her return journey to Plymouth from France. Once she is back in the UK it would be a good comparison against Poppy, I believe their hulls are similar.


    Mark

  • 05 May 2019 12:23
    Reply # 7322903 on 4913961

    So here I am at Preston dock. I set up the kit yesterday afternoon, but was too tired to do a run, after having to fix the outboard in the morning. However, everything connected up properly.

    This morning it was flat calm and still water, and we did the calibration run. That went OK, except that at speed and horizontal, quite a lot of water was going over the top of the float. It seems to be best to tow it at 3˚ bows-up.

    Then I did a run with miniplex3 config recording a txt data file. Of course the actual figures are meaningless, but it will give you something to look at and process.

    It took a couple hours to set up the first time, but familiarity will improve on that. It took an hour to break down and stow the kit again.

    I don’t fancy my chances of doing any real testing until I reach Falmouth, unless I stop in Milford Haven and do a bit there. The wind looks turning fair on Wednesday and Thursday for the passage down to there.

    8 files
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

                                                              Site contents © the Junk Rig Association and/or individual authors

Powered by Wild Apricot Membership Software