Sadler 25 conversion..

<< First  < Prev   1   2   3   4   5   ...   Next >  Last >> 
  • 24 Sep 2020 10:22
    Reply # 9261659 on 8800878
    Anonymous member (Administrator)

    I choose to answer on this thread, as I don't want to hijack this one...

    Arne

  • 23 Sep 2020 20:16
    Reply # 9260271 on 8800878

    I remember standing on the deck of Johanna with Nils Myklebust viewing along a panel from luff to leech while I tried to measure the depth of camber from his direct view and the sail material. This way we were measuring the max depth of camber from luff to leech. If you measure from batten to batten as it Arne's photo you have to make allowances for the thickness of the batten  and possibly measure both sides of the sail if the battens are fastened to one side of the sail, which is often the case.

    Maximum camber is not necessarily going to give the best information. A lot depends on the shape of the camber from batten to batten, whether it is a 'V' shape or a broad flat 'U' shape. The cross sectional area of the camber might be as important or even more so. 

    Think of a tinplate horizontal shelf foot panel where the camber would be at maximum depth over the full height of the panel, and compare that to a simple soft material with an arc of a circle cross section. There would be quite a difference in the area of the camber shape and therefore it would seem a difference in resultant performance.

    This suggests that the different methods of camber construction could have perhaps as much effect on the performance as the maximum depth of camber. The flat shelf foot would probably have the biggest cross sectional area for a given maximum camber depth, the 45° angled shelf foot might come next, but that might depend on how the broadseam was designed and how many seams were used in a 'round and broadseam' panel. The simpler to construct round only panels might have the lowest cross sectional area for the same maximum camber, but with a simple increase in maximum camber could have equal camber area.

    What I'm suggesting is that simple camber numbers might give misleading impressions, and that maximum camber and camber construction would probably be needed to form a realistic comparison. I dreamt up the angled shelf foot as a means of getting as flat a cross section camber right from the luff of the jib panels, and of course the leech ends become  more like the arc of a circle, and this is why I am still struggling to find the ideal shape for the jib panel camber. What we are now using is not my ideal, but it seems to work well and until someone finds better it is well worth using.

    Cheers, Slieve.

    Last modified: 23 Sep 2020 20:20 | Anonymous member
  • 22 Sep 2020 23:20
    Reply # 9257999 on 8800878

    Ah! Thanks Arne that's the photo I was looking for (couldn't find it)


    When making comparisons between SJR rigs, as these rigs develop and evolve, I hope we can keep a record of the design paramaters (mains camber, jibs camber, top panel camber and sheeting angle.) It makes sense in this case to record the designed camber of the shelf-cut components.

    However, as Arne is suggesting, the designed camber of  a shelf constructed panel might turn out to be different from the actual camber, as measured by Arne's method. I am not sure if anyone has checked this. My guess is that the actual camber will turn out to be a little bit greater than the designed camber.

    Anyway, for the purpose of comparing camber between the panels of a shelf-cut sail, and the panels of a broad-seamed sail or a barrel-cut sail (should one wish to do that) the camber ought to be measured using Arne's method as illustrated in his photo above, if we wish to "compare apples with apples".

    (PS just a leg-pull here Arne: for the problem of black oxide staining at the mast, one possible solution is to put a slot in your sail at that point.)

    (PPS Paul, while I share and agree with your admiration of Slieve's concept and creation, the calculated camber of a shelf-cut panel is not the result of a round and broadseam calculator but the result of simple trigonometry -  in the case of a 45 degree shelf it is simply the camber given to the shelf, divided by 1.4142)

    Last modified: 23 Sep 2020 02:49 | Anonymous member
  • 22 Sep 2020 22:47
    Reply # 9257929 on 8800878

    Hey Thanks Arne, 

    and thanks for the album tip- yes my IT skills are non existent,I’ll try and sort them in due course.

    The camber is calculated camber, and arrived at by magic- using Slieve’s fabulous Round and Broadseam calculator.

    I just entered the parameters supplied by Slieve and it spewed out all the relevant measurements..

    Slieve felt that a slightly flatter main panel at 7% was worth trying (I think many of the previous incarnations used 8%), as he believes most of the drive comes from the Jiblets. Knowing nothing of these matters I simply followed all of his suggestions to the letter- it was a good feeling, Slieve was actually building my sail via remote control, all I had to do was put the hours in!

    If it would be of interest to you or others, I’d be happy to measure the actual camber next time I’m out.


    BTW - my Arne Yard looks great on top of my rig.

    So thinking about it my conversion is quite a melange..

    I’ve got a -

    David Tyler Masthead Unit (and I think the sheeting arrangement sent me by Edward Hooper may be David’s as well)

    Arne Kverneland Yard and Mast Step

    Slieve McGalliard Split Junk sail

    .....talk about standing on the shoulders of giants.


    Cheers

    Paul

    Ps there’s even a bit of me in it too- I did the Mast Partners..

  • 22 Sep 2020 13:10
    Reply # 9256304 on 8800878
    Anonymous member (Administrator)

    Congratulations, Paul,

    and welcome in the club of efficient JRs! Your description of your first sail, the super easy tacking and manoeuvres, and also of your downwind speed, sounds like a copy of my own experiences. I still, after almost 30 years with cambered JR, haven’t got 100% used to it. It happens that I crew in Bermuda-rigged boats, and then I quietly congratulate myself for not ‘being there’.

    I have looked through your albums. Lots of fine work to be seen. I realise that I should paint or varnish the aluminium mast (..next time...), and maybe even the batten ends. The black oxide on the untreated aluminium begins to show on the sail at the mast. In addition, I wonder if a varnished mast has lower friction in it.

    One little member’s album trick:
    The photos there are being sorted according to the original file names they had in your computer. To keep control of the position of the photos in the album, I make a ‘ghost album’ in my computer, and give the file names a prefix, starting with z1000000 01, z1000000 02, etc. I can even insert in a photo between others, by calling it z1000000 02.5, for instance.

    Cheers, Arne

    PS: You mention that the main sail panels have 7% camber. Is that calculated camber or actual, measured camber?


    Last modified: 22 Sep 2020 21:59 | Anonymous member (Administrator)
  • 22 Sep 2020 09:40
    Reply # 9255934 on 8800878

    Thanks guys,

    congrats to you too Jami on your beautiful yellow sail..

    Ed, I’ve gone initially with the sheeting as per the diagram you sent me, will also try your split sheet system in due course.


  • 22 Sep 2020 03:47
    Reply # 9255476 on 8800878

    Wonderful, congrats!

  • 21 Sep 2020 17:23
    Reply # 9254102 on 8800878

    Bloody marvelous Paul.

    I agree the picture of your feet and the mast and sail says it all.

  • 21 Sep 2020 09:13
    Reply # 9252498 on 8800878

    Congratulations Paul. 

    What a super addition to the SJR fleet. Now for the fun part. 

    Enjoy. Ed. 

  • 20 Sep 2020 18:02
    Reply # 9250933 on 8800878

    Thanks Guys,

    courage? That’s why I bought cheap cloth haha

    knowhow? Me neither, but I know a man that does..

<< First  < Prev   1   2   3   4   5   ...   Next >  Last >> 
       " ...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