Measuring junk sailing performance

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  • 09 Jun 2019 11:15
    Reply # 7568157 on 4913961

    Hi Arne,

    That is all clear now.

    You are correct that Blondie's lead might well be 17%. The idea of putting a plate on the bottom of the rudder is always on my mind when I haul out but usually I'm only out for 2 days and I never have enough time to do it properly - maybe next time.


  • 08 Jun 2019 10:05
    Reply # 7564995 on 4913961
    Anonymous member (Administrator)


    I expressed myself unclearly. What I meant, was that my range of Johanna-style sails can be set with a balance between 12 and 17% (with respect to mast), or even 10 to 17% on the sails with higher aspect ratio. The position of the slingpoint sets the final limit for the sail balance (we don't want it to touch the mast.). If you want to increase to 20-22% balance, then the yard angle must be reduced. However, changing from the present 10% to 16-17% should make a big difference to the helms balance.

    On the first two trips with Ingeborg, in 2016, the sail was set with about 12% balance. To trim away most of the weather helm, I increased the balance to 15-16%, by both lengthening the  standing tack parrel, TP (in harbour, before next trip), and then using the yard hauling parrel, YHP, to bring the halyard’s slingpoint closer to the mast.

    I don’t have a running TP, so I can only shift the top of the sail back and forth under way by playing with the YHP and the tack hauling parrel, THP. I generally don’t bother. To remove the last bit of weather helm on Ingeborg, I would have needed to lengthen the batten parrels and maybe even the fore batten pockets. I haven’t bothered. I need to reef in the middle of F4 and then the weather helm is reduced.

    I have been pondering the idea of making another sail for Ingeborg, very similar to the one I have, but with the camber increased from 8 to 10%. Any armchair speculations about the outcome of such a change is useless; only full-scale sailing will do. In case I go ahead and do it, I will reduce the batten length from 4.90m to 4.75m, and the batten parrels will be made long enough to allow a full 17% balance.

    Clear as mud, right?


    PS: Now I looked up your boat in your album. By measuring with a yardstick on the screen, it appears to me that your sail is already setting with 17% balance. How is your rudder? Could it be improved by simply gluing on an endplate?

    Last modified: 09 Jun 2019 16:18 | Anonymous member (Administrator)
  • 08 Jun 2019 02:54
    Reply # 7564680 on 4913961

    Interesting comments, Arne.

    You mention that Ingeborg has a balance of 12-17%. I know this is a basic question but why is there a range of balance percentages? Do you adjust it whilst sailing? Our boat Blondie with your cambered sail plan has a balance of 10% that was the recommended figure but she does have some weather helm. Is it possible to increase the balance and maybe reduce the weather helm? Is there a balance percentage maximum with your cambered sailplan? Is 20% possible? I am asking this in relation to our new boat rather than for Blondie.


    Last modified: 08 Jun 2019 02:55 | Anonymous member
  • 07 Jun 2019 13:52
    Reply # 7563441 on 4913961
    Anonymous member (Administrator)

    I find the shown pointing angles, 32-36°, to be good, but not spectacular. Only on my present boat have I fitted a simple wind-direction indicator. This has the vanes set at 32° from the centreline. I find that I can quite easily sail this close with my plain, single-ply, cambered panel sail.  My guess is therefore that the big, dominating gain in performance has been achieved by going from a flat to a cambered sail. The extra step up to Split JR or wing JR will only produce fine, subtle improvements, if any at all.

    (.. My present boat, the IF Ingeborg, is special. Her slim hull and big keel make very little leeway, so she is actually closer-winded than any boat I have owned before...)

    As for keeping my boats in the groove when close-hauled; I find that quite easy, as that groove is fairly wide, and the luff of the sail and telltales at the leach are easy to read.

    My motives for choosing a Split  JR would therefore be others than performance to windward:

    ·         The sheet forces of a SJR are clearly lighter than on a sail with lower balance in it, like mine (12-17%). That would be useful, in particular when day-sailing and racing with lots of manoeuvring.

    ·         Helms balance stays better when reaching and running, so no need to modify the rudder or arrange with adjustable sail balance.

    ·         The squared-out SJR sail should also have better clearance to the sea than my wide low-balance sails.

    ·         Its batten parrels cum downhauls appear to also act as active fan-up preventers. Good!

    ·         In some cases, the high-balance sail would let one step the mast further aft, which may better suit the deck layout and interior. In other cases a low-balance sail fits better.

    ·         The SJR could even be made by an amateur like me.

    The Wing JR would never be my choice, simply because my ambition level with respect to VMG to windward  -  and my skills with GRP or epoxy  -  are not high enough. I rather choose a close-winded hull where the outboard’s leg can be swung up.

    Anyway, good luck!

    Last modified: 09 Jun 2019 09:56 | Anonymous member (Administrator)
  • 07 Jun 2019 10:34
    Reply # 7563211 on 7563190
      Edward wrote:

    Hi All,

    Yes Weaverbird did point higher, but more like 2° to 3°,  but that was, for me, not the main lesson. 

    What really impressed me was the ‘tolerance’ of the soft wingsail, when close hauled.  Amiina has quite a narrow ‘groove’, on the wind, between luffing and stalling.  The soft wingsail seemed to me to be more tolerant, with a wider groove. 

    Other points to note.  Weaverbird is in full cruising mode with lots of stores etc. onboard, and with her outboard down all the time.   On the other hand, she is a 25 year, or more(?) more modern hull design, with 2 foot longer waterline, and 22/25(?) sq. m. sail.  Amiina has only 173 sq. ft. (16.1sq.m).

    The Splinter was first built in 1963, the Sonata/Duette in 1976. The difference in LWL is 1.42 ft. Weaverbird has a 22 sq m sail. The displacements are very similar, but the Sonata has more beam.

    Yes, Slieve, it would be naive to read too much into the work we've done in the last few days, but equally, it would be a mistake to read too little or dismiss it as worthless, and it would also be a mistake not to try to gather data, however stumbling these initial efforts might appear to be. We have to start somewhere. Doing nothing won't help us to improve the breed.

    From the cruiser's point of view, it's the tolerance of the wing sail to inattentive helming, and steering by vane gear, which is one of the positive gains. A day racer, or an ocean racing helmsman who only takes an hour on the helm before being relieved, can afford to concentrate hard on staying in the groove. A cruiser who needs to round a headland before the tide turns, or make the anchorage before dark, also benefits from good performance, but it shouldn't be too hard to attain that performance. Good performance achieved with the least input of effort from the crew, is my principle aim.

    Last modified: 07 Jun 2019 13:25 | Anonymous member
  • 07 Jun 2019 09:58
    Reply # 7563190 on 4913961

    Hi All,

    Had a very interesting and illuminating day with David Tyler and Weaverbird here in Poole Harbour.  David Harding, noted journalist with PBO and Yachting Monthly, was watching closely.  There will be some good photos and maybe an article to come out of it. 

    Yes Weaverbird did point higher, but more like 2° to 3°,  but that was, for me, not the main lesson. 

    What really impressed me was the ‘tolerance’ of the soft wingsail, when close hauled.  Amiina has quite a narrow ‘groove’, on the wind, between luffing and stalling.  The soft wingsail seemed to me to be more tolerant, with a wider groove. 

    Other points to note.  Weaverbird is in full cruising mode with lots of stores etc. onboard, and with her outboard down all the time.   On the other hand, she is a 25 year, or more(?) more modern hull design, with 2 foot longer waterline, and 22/25(?) sq. m. sail.  Amiina has only 173 sq. ft. (16.1sq.m).

    The sea was pretty flat, in Poole Harbour Upper Triangle. Wind SW F3 to 4.  Fairly steady. , top of the tide, so little tidal effect.   Shows the importance of more like  to like trials, with same hulls and same sail areas. 

    Cheers, Edward

    ps. Whatever happened to our old title “ Junk Rig and Advanced Cruising Rig Association”. 

    With ever increasing commercial interest in soft wing sails, is it timely to resurrect our former mission?

  • 07 Jun 2019 09:39
    Reply # 7563164 on 4913961

    There would be something very wrong if a rounded luff wing sail with an enclosed mast did not beat any single surface rig with exposed mast in a pointing/ beating test, all other things being equal.

    Although they are around the same length, the hull forms of Weaverbird and Amiina are completely different, as are their appendages. The boat stats for each design are miles apart. Despite that, it would appear that, boat on boat, the only performance difference is really down to the differing opinions of the two skippers on pointing ability.

    Here we clearly see the weakness in this form of testing. Inevitably it will boil down to guestimates and fudge factors set by the testers to prove any point they want, which are totally unacceptable in a proper analytical test. This is similar to our politicians (mis)use of statistics

    Even with highly accurate computerised calculations and plotting, and results will be no better than the measurements with their associated calibration errors and which will not necessarily be the same on each boat tested. Sea state will be different for each test, and every hull shape will react differently to different sea states.

    It would be a grave mistake to read too much into these tests.

    Cheers, Slieve.

  • 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˚!

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

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

  • 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.

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