Freedom 40 Cat Ketch Junk Rig Conversion

  • 14 Sep 2017 20:54
    Reply # 5261203 on 1424184
    Deleted user

    David:  Great instructions and I will draft both the halyard and topping lifts now.


    Batten Parallels  - I seem to recall the advice of having a 30 degree angle between the batten and the mast.  At 15% overlap, this angle to the forward end of the batten is more acute, can I do 30 deg or larger (more preferred if it helps in keeping the battens from going forward).   


    This being a double masted rig, I don't see a need to move the sail when sailing downwind to balance things since I can go wing-on-wing.  I could see the parallel tension going more slack if the angle is not 30 degrees as the batten has to move from the 250mm diameter mast at the base (and that diameter up some 7 meters) to somewhere higher and skinnier.  In order to help tension the BPs on the upper battens, I was wondering if I can utilize the throat parallel.  The BP, rather than being fixed at the end of the batten would go through a small block tethered to the end of the batten,  and then terminate a single, free floating block.  The THP would go through this last block.  Tension on the THP would then tension the BP.  Stopper knots could moderate the amount of travel in the BP.  When the sail is dropped, the THP goes slack and the BP could "lengthen" to accommodate the larger diameter mast.  See drawing to aid the description.




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  • 14 Sep 2017 19:58
    Reply # 5261073 on 1424184

    The halyard tackle, fixed as usual to the middle of the yard, must have enough drift such that when the yard goes to +/- 90 degrees, the rope doesn't make too great an angle with the sheaves of the blocks, otherwise damage will result. When a span is used at the yard end of the tackle, some extra freedom is allowed the lower block, as the span itself can twist a bit, as well as whatever rotational freedom there may be in the shackle and thimble. This means that the block to block distance when a span is used can be somewhat shorter than when a direct yard connection is used.

    When making the design, I would first mark the points at the one third and two thirds points of the yard, and also at the centre. I would then draw a line from the two thirds point to intersect with a line from the masthead block to the centre of the yard, such that the  angle between the yard and this first line is 30 degrees. Then draw another line from the one thirds point to this intersection, and this will be the shape of the span that you are aiming for. Then allow let's say five times the length of the halyard block for the tackle - two blocks plus the length of three blocks between them. I have found this to be enough drift.

    I tie an alpine butterfly knot (which can take a load in two directions) in the 6mm Dyneema at the intersection point, large enough that a full turn can be taken around the bow of the shackle on the lower halyard block. I tried a stainless steel thimble here, but it soon failed due to fatigue. The 6mm Dyneema should be tied right around the yard at the one third and two thirds points, with a strong eye just to keep them from sliding, not to carry the load.

    I use Dyneema for my lifts as well. I would use 6mm for yours. I tie two forward lift lines halfway down the topping lifts (to an alpine butterfly again) one on each side and lead the line on the mast side to the bottom batten/boom at the after end of the batten parrel, and the line line on the other side to a point level with the mast line. Actually, a span at the bottom of this latter line will help with gathering the bunt of cloth here.

    The reason for doing the forward lifts in this way is twofold. It stops the annoying clatter from a lift that is parallel to and close to the mast; and more importantly, it brings the line of the topping lifts further forward. With the weaverbird planform of sail, I have found that a gybe with three panels up is safe enough without this form of forward lift, but a gybe with two panels up risks getting the yard trapped behind the topping lifts. This planform of sail seems to be much less prone to misbehaving during a wild weather gybe than the HM kind; but there is still a risk, even when the yard has a light extension to bring it to the same length as the lower battens (essential). Moving the topping lifts forward is the cure.

    Last modified: 14 Sep 2017 20:01 | Anonymous member
  • 14 Sep 2017 19:08
    Reply # 5260935 on 1424184
    Deleted user

    Thanks for the input David.  Since my sail is of the Weaverbird type (seem appropriate for a boat called "Raven")  and the bridal is possibly an option, do you have some input on halyard drift and lifting point on the yard? I have plenty tall masts at present, but would like to come up with a realistic number - 0.3B is suggested in PJR, but the yard is significantly shorter and at a lower angle than the "classic" rig.  This would then help lock in the lazy jacks.

    Speaking of the latter - Is it correct that some people are doing away with the mast lift and relying on the topping lift with one line further forward to gather the sail and balance the bundle.  Pros and cons?

    e

    headed out today to look at battens and yards :)

    Last modified: 14 Sep 2017 19:54 | Deleted user
  • 14 Sep 2017 08:27
    Reply # 5202953 on 1424184

    How traumatic is a yard breakage? Very. You can break a batten, mid-ocean, and lash it to the next one and carry on. If you break a yard, you have to fix it.

    Does a bridle or span help to spread the load? Yes. I've done it, using 6mm Dyneema.

    If I remember correctly, Footprints has had a yard of 100mm dia, and this wasn't enough - but the length was much greater than your proposed yards, and it was probably T5 temper. My guess is that 4" dia T6 with a span to spread the load will be more than adequate.

  • 14 Sep 2017 00:28
    Reply # 5164767 on 1424184
    Deleted user

    Formatting of the last post looks off on my screen.  Sorry about that

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    Webmaster Edit: Table realigned in last post.

    Chris

    Last modified: 14 Sep 2017 07:22 | Anonymous
  • 14 Sep 2017 00:27
    Reply # 5164666 on 1424184
    Deleted user

    Arne and Paul - thanks so much for the input.  My yards are at 45 deg and the sails are high aspect with a typical ketch (steep) sheeting angle.  The sail on Edmund Dante is similarly sized, but the yard at 70 deg. and at 6 meter length about twice that of mine - 3.2m on the main and 2.7m on the foresail.  I don't know conceptually how the loads will differ in these two plan forms.  

    Some numbers comparing sections (cross sectional area would indicate relative weight, Iy and Ix stiffness/strength in the vertical and horizontal).


    Cross Sec.
    A  mm^2
    Iy mm^4 Ix  mm^4
    A. 150mm x 3 mm 1,385  3,738,888  3,738,888
    B. 80mm x 5mm +
    50mm x 1.5mm
    1,406 1,751,154 569,347
    C. 127mm x 3.175mm 1,244 2,382,815 2,382,815
    D. 100mm x 3.175mm 965 1,131,518 1,131,518

    (A) is the workhorse and can take the largest loads.  (B), the combination of two tubes, is the most narrow and would have the least windage.  (C) and (D) are 5" x 1/8" and 4" x 1/8" (yes, this is the US) and are easily available.   

    If one were to assume that (B) has adequate properties, then (C) would be plenty strong and lighter.  The gamble is whether (D) would work.  Would using a bridal to spread the halyard loads help.  

    So the question is - How traumatic is a yard brakeage?  :)

    Cloth is coming on the 15th.

    Erik


    Last modified: 14 Sep 2017 07:20 | Anonymous
  • 09 Sep 2017 09:42
    Reply # 5071620 on 1424184
    Anonymous member (Administrator)

    Erik,

    If you look up part 2 of the story about making a new sail for Edmond Dantes, you will see that we made the yard from two tubes, one of 80 x 5mm and one of 50 x 1.5mm. This held up very well ,even at a length of almost 6m. The sail was 48sqm and the displacement of ED is about 4 tons.

    I think your Freedom 40, at 9 tons, and with two masts and much shorter yards, will do fine and be safe with the same scantlings as on used on ED. I have used this two-tube way of building yards on three boats now without problems, but you could also have the upper tube welded on as a brace, as done on my Johanna. 

    Arne


  • 09 Sep 2017 01:07
    Reply # 5071265 on 5069722
    Erik and Evi Menzel Ivey wrote:

    Some questions regarding battens...

    I think previously folks have recommended that the boom and battens could be 50mm x 1.6mm.  When counted from the bottoms, the transition battens for Panels 5 and 6 would be same diameter but 3mm wall.  What about the yard - single tube, 100mmx3mm wall?


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    150 x 3 would be safer, and please note all tubes Battens and yards must be T6 temper else you'll have bending problems.
  • 08 Sep 2017 05:25
    Reply # 5069722 on 1424184
    Deleted user

    Some questions regarding battens...

    I think previously folks have recommended that the boom and battens could be 50mm x 1.6mm.  When counted from the bottoms, the transition battens for Panels 5 and 6 would be same diameter but 3mm wall.  What about the yard - single tube, 100mmx3mm wall?


    e

  • 08 Sep 2017 05:16
    Reply # 5069719 on 5052868
    Deleted user
    Arne Kverneland wrote:

    Erik...

      -  it's about time now, don't you think?

    Cheers, 
    Arne


    Progress maybe....    The foresail design is (somewhat) finished (till I change my mind) in 3D and laid out flat in QCad.  Actually this has been enough of an effort that I am not going back.  :)

    Originally I kept the same profile at the battens along each panel - max draft at the second seam, flat section from the 3rd seam to the luff, but reducing the amount of camber from 8% to 4 and then 2 in Panel 5, 6, 7.  This resulted an adequate shape for Panels 1-4 (as counted from the bottom).  But for Panel 5-7, when looking at a horizontal cross-section, the effective draft was too far back.  The solution was to have max camber at the first broad seam for these panel, which got the draft - looking in a horizontal cross-section - forward of 50%.  Some pictures, to make sense of my less than adequate description have been uploaded in this album  .  


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       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
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