The Aerojunk

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  • 23 Jun 2013 14:15
    Reply # 1325092 on 1152568
    Dear Arne, I was asked a couple of interesting questions yesterday from John Hess of the Yahoo Junk Forum. This is the reply I gave him which crystallises what I have been thinking for years.

Would you mind refreshing my memory what the rationale for your design is? If you take a flat piece of cloth and fit straight battens you have a flat sail and the Up Wind Performance of a Chinese Junk Sail.

                       If you take a flat piece of cloth and fit it inside wishbone battens you have a cambered sail and the UWP of a Lugsail.

                       If you take 2 flat pieces of cloth and fit them inside wishbone battens you have 2 cambered sails + the 'slot effect' and the UWP of a Bermudan Rig. Also my design needs between 25 and 34% of the total sail area in the jib. This means the mast has to go further back than a normal Junksail. So for many boats, the mast can go in or beside the same position as the Bermudan mast.

    Why is the forward end of the battens separated by a spreader, but not the aft end?

    The forward spreader allows the jib more room to develop a camber whose strongest curve is close to the leading edge, just like an aircraft wing. This is what gives my sail plan its great light weather performance and lesser tendency to stall. The aft end does not need such a spreader.

    Regards, Paul

  • 22 Jun 2013 14:47
    Reply # 1324612 on 1152568
    Thanks again Arne. My cunning plan is to fit tell-tales as soon as I get a windless day. My boat is in the marina now and I need to raise full sail before I can stick them on. So far the wind has been behind my berth!
  • 22 Jun 2013 14:43
    Reply # 1324611 on 1152568
    Dear Arne and others, I will publish full details of my experience with this rig in the next newsletter but if anyone wants to experiment over the summer these are my batten details.
    The battens are made from 1"x1/2" rectangular aluminium tube. These come in 5 metre lengths and weigh 0.3 kilos/metre. I bought mine from Richard Austin Alloys. Bought singly they cost £25 each including VAT. Bought as a bundle of 14 they cost £10.80 each inc vat.
    The cross-rods are cut from 8 mm 316 grade Stainless Steel rod also form Richard Austin. These come in 3 metre lengths and cost about £16.20 each including vat.
    The tubes are marked and drilled for the jib and main luff and leech eyelets. Each tube is drilled right through for the main luff and leech and the jib luff. The jib leech is drilled on the insides only. The main leech is positioned then a 7.6 mm cable tie is threaded through it and both tubes and pulled loosely to start with. The cross-rod is inserted through the jib leech and the rod ends inserted into the socket holes. Next the jib luff is threaded with 2 cable-ties, centred then pulled tight through both tubes forming the wishbone. Finally the main luff is threaded with 2 or 3 cable ties, centred then pulled tight through both holes. Lastly the aft battens ends are closed with a small riveted alloy plate, a bull's eye block screwed on and the aft cable tie finally tensioned.
    7.6 mm cable ties can hold a pull of 50 lbs (22.6 kilos). Where the sides of the battens touch the mast they are cushioned with pieces of 15 mm plastic plumbing pipe.
    The wishbone battens get their shape from the S/S rod pushing the sides out against the tension of the fore and aft cable ties and are prevented from falling out by the tension of the main luff cable ties. This means that the tubes do not need to be bent first. I have a gap of 150 mm (6") between the jib leech and the main luff to allow room for the mast.
    Happy experimenting! 
  • 22 Jun 2013 12:26
    Reply # 1324546 on 1152568
    Anonymous member (Administrator)

    Good Paul. Now I had another look at the photos and surely like the camber of the sail, not least close to the luffs.

    One thing: I cannot see any telltales - is there a cunning plan behind that? Personally I feel more or less blindfolded when sailing boats without any telltales. It is sooo easy to over-sheet a sail and stall it...

    Cheers, Arne

  • 22 Jun 2013 11:41
    Reply # 1324533 on 1152568
    Yes Arne, one halyard with a 3:1 purchase, one sheet with a simple clamcleat and one fixed downhaul fastened to the boom by the mast. However I am going to fit adjustable downhauls to battens 1 and 2. This means I should have a properly tensioned sail with 5,6 or all 7 panels.
    This I hope will give me performance with comfort and relatively upright sailing.

  • 22 Jun 2013 10:21
    Reply # 1324508 on 1152568
    Anonymous member (Administrator)

                                                                    Stavanger, Saturday

    I always take a closer look when you present an idea, Paul. Your article in PBO in 1989 about your "Fever" with a wishbone junk, told me one important lesson: From an aerodynamic point of view a junk sail is just another sail - well that was how I understood it. This encouraged me to search for ways of adding camber in Malena ’s first sail when I found it to lack upwind performance in flat mode.

    Thanks for your answers. I can well see that you get away with a single sheet, just as with the Aero Rigs (Bermudian style). My second question was because I didn’t see that the jib was controlled with more than one clew. Now it appears that you have several "intermediate clews" to control the sheeting of the jib even when reefed. This looks good.

    Does it mean that you now only need one halyard and one sheet and no other running lines at all? No downhauls?


    Last modified: 22 Jun 2013 10:25 | Anonymous member (Administrator)
  • 22 Jun 2013 01:08
    Reply # 1324311 on 1152568
    Dear Kurt and Arne, thanks for your very kind comments. To answer Arne, the sailplan is so balanced that I only need to use a single line sheet. It runs through bull's eyes on the batten ends. I have tried it all the way to the top batten and also to batten 5 (last horizontal) Both work. When reefed the sail stays put so no need to use sheetlets. Also I have been able to use the original sheet-track in front of the cabin hatch so no more miles of rope round your head on each tack!
    The jib leech at each batten runs on a S/S slide rod so the jib is self tacking even when reefed. ( It is the jib slide rod that spaces and tensions the two halves of the batten so no need to prebend anything.) The sail works well in very light winds. My next test is to be in stronger weather.

    Regards, Paul

  • 21 Jun 2013 19:12
    Reply # 1324074 on 1152568
    Well done, Paul!

    So many concepts don't get the benefit of such hard work and investment.
    Promising potential. Thanks for the photos.

  • 21 Jun 2013 16:50
    Reply # 1323961 on 1152568
    Anonymous member (Administrator)

    Paul, this looks pretty aerodynamic!

    Two questions:

    • Do you plan to use JR sheeting?
    • What happens to the sheeting of the jib if you reef?


    Last modified: 21 Jun 2013 16:51 | Anonymous member (Administrator)
  • 20 Jun 2013 21:23
    Reply # 1323263 on 1152568
    Greetings, fellow members, the AeroJunk has gone from theory to practise. After 2 weeks of experiment and adjustment, I had my first successful sail today in the very light winds I designed it for. I have uploaded 5 photos in the gallery. I will be interested to hear your comments, good and bad.
    Regards, Paul
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