Kittiwake 23 JR Conversion

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  • 01 Aug 2019 12:56
    Reply # 7807228 on 7804871

    Arne,
    That's tremendous, overlaying the two of those. What do you think about the two different CE positions, for this boat? One better than the other? That's so sweet of you, drawing this up!
    Shemaya

  • 31 Jul 2019 20:44
    Reply # 7806259 on 7806089
    Anonymous member (Administrator)
    Janine wrote:

    Arne & David, Thank you so much for your replies! 

    We (Shemaya and I) asked the flagpole manufacturer about the weight given and are waiting for a response. Will let you know when we hear back from them. 

    Arne, thank you SO much for drawing the Johanna type rig! I started out with that one but got lost early on trying to figure out the total area. Your work has put it back into the 'possible list'. Thanks again!






    Hi again, Janine.

    Now I have done my best to superimpose the Reddish rig onto my first drawing to see how they compare.

    Arne

    To scale one of my Johanna style master sails up or down, it is best to use a calculator, as described in The Cambered Panel Junk Rig (TCPJR), Chapter 4.

    Arne


    Last modified: 31 Jul 2019 20:45 | Anonymous member (Administrator)
  • 31 Jul 2019 20:32
    Reply # 7806233 on 7804871

    I think that the mast weight given might be including the other flagpole mounting bits, one of which is a 2 foot steel sleeve for below the ground. With luck we'll hear back soon about that. Thanks for picking up on that, David!

    Shemaya

  • 31 Jul 2019 20:03
    Reply # 7806160 on 7804871

    Now I'm sure the mast weight is too high. I calculated the weight of a parallel 8.23m tube, 15.2cm diameter  and 5mm wall, and it comes to 51.3kg. But the tube is tapered, so the weight has to be less than that. I guess it's in the same region as mine, around 40kg, which is perfectly acceptable.

    Last modified: 31 Jul 2019 20:04 | Anonymous member
  • 31 Jul 2019 19:20
    Reply # 7806089 on 7804871

    Arne & David, Thank you so much for your replies! 

    We (Shemaya and I) asked the flagpole manufacturer about the weight given and are waiting for a response. Will let you know when we hear back from them. 

    Arne, thank you SO much for drawing the Johanna type rig! I started out with that one but got lost early on trying to figure out the total area. Your work has put it back into the 'possible list'. Thanks again!





  • 31 Jul 2019 16:22
    Reply # 7805709 on 7804871
    Anonymous member (Administrator)

    Now, I couldn’t resist trying how such a Kittiwake 23 would look like with one of my standard Johanna-style junkrigs on it.
    I drew up a mast, reaching 8.00m above the waterline, and then tried a couple of sails, scaled down to B=4.00m. Its balance of 15% with respect to the mast gives a bit room for shifting it forward or aft to fine-tune the steering balance.

    The tallest sail which could be used with that mast, was the one with AR=1.90. That one happens to be the same as I use on my Ingeborg (except B=4.90m on Ingeborg). As can be seen, this sail gives a respectable sail area and luff length with a not too tall mast.

    As for the control lines, sheet, etc, I use those shown on Junk Rig For Beginners, plus a Fan-up preventer.

    The advantage with the sails with an upright leech is that one avoids having any sheet-batten tangle. Several identical panels also speed up the construction of the sail.

    Just a thought

    Arne



    Last modified: 31 Jul 2019 19:16 | Anonymous member (Administrator)
  • 31 Jul 2019 12:53
    Reply # 7805353 on 7804871

    I'm a little surprised at the quoted mast weight, and I'm wondering whether it's correct? My flagpole mast tube is 9.2m long, 17.7cm diameter at the base, 7.6cm diameter at the top, 3.2mm wall thickness, and only weighs 36kg. Add in the top and bottom fittings, and the conduit, and it's still under 40kg. I do like a mast to be stiff, and this means greater diameter and less wall thickness, for a given weight. Is there an option with a .125" wall thickness?

    Onto that, I can put a reasonably high AR sail of 22 sq m, with battens about 3.375m long. The low AR fanned sails such as the Reddish, and the ones that we made for Fantail, Tystie and Footprints, look nice and are reasonably efficient, but now, I've come to prefer the higher AR planform for its greater efficiency and greater ease of handling. The Reddish planform will certainly look well on your boat, Janine, but have you checked that the sheet blocks can be rigged far enough aft? The curved leech will mean that they have to be further aft than for a sail with a straight leech.

  • 31 Jul 2019 09:29
    Reply # 7805240 on 7804871
    Anonymous member (Administrator)

    Janine,
    that looks like an elegant little boat for a JR!
    Now, I have looked on the numbers, and it seems to me that the mast is a bit on the strong (read: heavy) side. It will add about 5% to the weight of the boat. It is not extreme, but it is a bit heavy. If I had that pole and could not find an alternative, I would use it, but if I had a chance, I would look for one with a bit smaller section. I know 6-inch masts have been used on boat in the 2.5 ton class. The 6063-T6 alloy is also very strong, so that is another reason for stepping down one size.

    Anyway, if you have to use the pole you have, and are to cut off some excess length from it, I suggest you cut at the thick end.

    That hull is probably very easily driven (similar to my Marieholm IF), and to keep the mast as short as possible, I would just use that 6-panel sail as it is.

    However, I suggest you build some camber (bagginess) into each panel, in particular in the four lowers, and also make use of Vincent Reddish’s method of inducing twist in the sail, to add (and control) camber higher up.

    Good luck!

    Arne


    Last modified: 31 Jul 2019 09:36 | Anonymous member (Administrator)
  • 31 Jul 2019 00:40
    Message # 7804871

    Miraculously, I'm actually getting to work on a JR conversion for a Kittiwake 23. Attached is a version of how this could go, with a Reddish rig. Thoughts?

    Information about the boat is HERE.

    Original sail area is 247 ft.² [22.95 m²]
    Reddish junk sail with 15 foot [4.57 m] battens, as shown in picture,
    is about 240 ft.² [22.30 m²] – an extra panel added to the bottom
    would bring this to about 270 ft.² [25.08 m²]

    Mast is 27 feet [8.23 m]
    6063-T6 aluminum flagpole 6 inch [15.2 cm] outside diameter, tapering
    (starting at 12.7 feet [3.87 m] from butt) to 3.5 inches [8.9 cm] at
    the top wall thickness: 3/16 inch (0.188 inch) [about 5 mm]
    weight: 186 pounds [84.4 kg]

    All of these measurements are "proposed" – nothing has yet been built.

    Thanks so much!
    Janine

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