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Junk Rig for Finch

  • 18 Dec 2017 19:27
    Quote
    Reply # 5641549 on 5631596
    Anonymous member (Administrator)
      

    Doug.

    Now I imported and traced the profile of the hull mast and your JR. I also found a cutter-rigged version on the web, which showed the position of the combined CE, right aft of the fore cabin window.

    Then I printed it out and found the CLR and CE of your sail, the old way. CLR1 is with rudder and CLR 2 is without rudder. Your CLR seems to be a bit aft of the CLR1. However, I can have screwed up, so better double-check.

    My experience with long-keeled boats has told me to be generous with the lead, so in my suggested (Johanna-style) sail, the CE has moved around 20cm forward. I hope that is enough. Your mast has a little aft rake. I would rather have it plumb or with 1-2° forward rake, in this case.

    Now I have sent the QCAD-file over to David Tyler, to let him play around with it, and probably add a sort of Weaverbird-rig to it.

    Arne.

    (PS: I do anything to postpone Christmas preparations...)

     
  • 18 Dec 2017 19:13
    Quote
    Reply # 5641523 on 5631596
    Anonymous member

    Hi Doug,

    I got the 195 sq ft from the note on the side of your sketch. That must have been a part area noted during your calculations, possibly for the bottom parallel section of the sail??

    Anyway, best of luck with the conversion, David.
  • 18 Dec 2017 11:11
    Quote
    Reply # 5632198 on 5631596
    Anonymous member

    Hi Doug,

    Good to see that you're thinking of a Weaverbird-style sail. Yes, 250 sq ft is too little sail, but 411 may be a little too much to fit onto a 30ft LAP mast. I'd go for 350 sq ft which gives SA/D = 18.

    At first glance, it seems possible to get a recognisably weaverbird-style 350 sq ft sail, AR 1.8 with batten length 15ft 5in onto such a mast. I've had a try at sketching such a sail - it doesn't look much like your sketch, though, as I don't think you've adhered to the same design principles as I have. As Arne says, you would need a longer mast to accommodate the sail you've drawn.
  • 18 Dec 2017 09:59
    Quote
    Reply # 5632144 on 5631596
    Anonymous member (Administrator)

    Doug,

    as for the shown planform of the sail; with the little balance and low yard angle, you will need a 0.5-1.0m longer mast. This is necessary to have the halyard pointing no more than 30° aft from the mast top to the slingpoint on the middle of the yard. The junkrig is not like the western lug where the halyard is attached well forward of the middle.

    The remedy is either to draw the sail with a higher-peaking yard (which brings the slingpoint closer to the mast), or, as said, lengthen the mast.

    In the latter case, David Tyler is the man to ask with respect to slingpoint and halyard drift.

    Arne

    PS:
    Btw, have you checked the CE of the junksail, compared to that of the original rig? Is the shown CLR including the rudder?
  • 18 Dec 2017 07:24
    Quote
    Reply # 5632056 on 5631790
    Anonymous member
    Doug Webb wrote:

    Finch is a pacific seacraft 25. 


    Oooh, nice boat.  One of the best: lucky you.  She'll make a wonderful junk - not too dissimilar from Shirley's Speedwell of Hong Kong, but more roomy.
  • 18 Dec 2017 01:04
    Quote
    Reply # 5631828 on 5631596
    Deleted user

    Thanks David.  On the sail area, from my measurements I believe the proposed sail is around 411 sqft. I certainly want to increase the sail area as the original 250 was very conservative.  I probably had less than 250 as Finch was a MKI, so she was a sloop versus the cutter, which, I believe is where they got the 250 sq ft measurement.

     

    Last modified: 18 Dec 2017 01:06 | Deleted user
  • 18 Dec 2017 00:38
    Quote
    Reply # 5631804 on 5631596
    Anonymous member

    Hi Doug,

    she is a nice looking boat. I note from information I looked up on the web that the designed sail area is 250 sq. ft. and that you are only providing 195 sq. ft.  It is more common to add sail area when converting to junk rig as reefing is so easy. It is possible that a split junk may give you comparable or more area than that shown on the original design, as it can have a lower overall AR but a higher AR for the individual sail sections. Others may have some comments on this.

    David.
  • 18 Dec 2017 00:19
    Quote
    Reply # 5631795 on 5631596
    Deleted user

    oh geez sorry no scale.  The mast is 30 above partners.  She is 26 feet LOA.  21 foot water line. 
  • 18 Dec 2017 00:17
    Quote
    Reply # 5631790 on 5631596
    Deleted user

    Finch is a pacific seacraft 25. 
  • 18 Dec 2017 00:15
    Quote
    Reply # 5631788 on 5631596
    Anonymous member

    Hi Doug,

    what design is Finch? She looks a bit like an Allegra 24 but the transom angle is too much for that design. Is she a Fred or Bruce Bingham design or someone else?

    All the best with the conversion, David.

    P.S. It would help if you could add a scale to the drawing of Finch.

    Last modified: 18 Dec 2017 00:16 | Anonymous member
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