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Gybing a junk

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  • 09 Sep 2014 23:51
    Quote
    Reply # 3096061 on 3093866
    Anonymous member
    Arne Kverneland wrote:

    Graham, what you described sounds rather to be a "Chinese gybe" than a partial fan-up: With much twist in the sail (Chinese, gaff or Bermuda), the gybe starts in the lower half and this gives a strong lifting effect of the boom. I have seen massive gaff booms lifting alarmingly when this happens. Again, I think the best remedy against this is to avoid much twist when sailing downwind in some breeze. Actually "negative" twist would be the best!

     

    Arne 

    Yes, I think you are probably right Arne.  I say probably as I didn't really see it, too much happening at once.  I was trying to adjust the course as the wind suddenly shifted, the boat was rolling violently in 3m seas and also I was trying not to get flung overboard.  Given how unsteady I am on my feet these days, it was quite a challenge!  I also suspect I didn't have the vang set up tight enough as I was worried about the strength of the boom.  I have now put a 2m sleeve inside the boom where the vang attaches.  Also, reviewing how I had my FUP set up, I think the angle of the vang was too shallow, maybe only 30 degrees to the boom, because I attached the block to an existing saddle on the boom (too far aft).  I am about to re-rig the FUP the way yours is set up and make sure the angle of the vang is 45 degrees. 

    I will also overhaul the sheet to reduce twist.  I can almost eliminate it, pulling the upper span back in a bit and feeding the sheet gained through to the lower span.  Accidental or flying (slack sheet) gybes are going to happen occasionally.  When you are running through a reef-strewn pass with no room to manouvre, and a shifting wind right up the stern, as I was last Saturday, you just have to take them.  I had the battens tied down to the boom that day so it was ok.  But tying the battens down is a pain, both to do it and to untie them again later when you want to rehoist sail (you have to bring the boom far enough inboard so you can reach the clew while standing on the side deck - the only time I leave the cockpit these days - and usually you have to round up to do that).  Your FUP should be a lot more convenient.
  • 06 Sep 2014 09:35
    Quote
    Reply # 3093866 on 1201045
    Anonymous member (Administrator)

    Graham, what you described sounds rather to be a "Chinese gybe" than a partial fan-up: With much twist in the sail (Chinese, gaff or Bermuda), the gybe starts in the lower half and this gives a strong lifting effect of the boom. I have seen massive gaff booms lifting alarmingly when this happens. Again, I think the best remedy against this is to avoid much twist when sailing downwind in some breeze. Actually "negative" twist would be the best!

     

    Arne 
  • 05 Sep 2014 22:54
    Quote
    Reply # 3093729 on 3092712
    Anonymous member
    Arne Kverneland wrote:

    Graham, it is funny that your present vang doesn't work. If your boom is resting in a mast lift and with a tack parrel keeping it from moving forward, then a vang at 45- 50deg angle aft should give a decent kicking-strap effect. Sounds mysterious...

    Arne


    It's a mystery to me too, Arne.  The conditions were extreme when it happened, rolling heavily in very steep 3m seas with squally winds but that's when you want it to work the most!  It seemed fine in milder weather trials.  Perhaps I did not have the preventer tight enough as my current boom is very light and takes a bend easily.  Also the geometry of my set up might have been less effective than yours, as the FUP line was attached only 40% back from the luff, came straight down to the boom then to the foot of the mast.  If it is a bit slack, the moment the boom starts to lift, the line goes even slacker.  I am off to Magnetic island, about 200 miles up the coast today and when I get there I intend to rig my FUP like yours and fit a strong boom.
  • 05 Sep 2014 22:35
    Quote
    Reply # 3093715 on 1201045
    Anonymous member

    Barny has alloy yard and boom with grp battens supplied by Sunbird Marine.The yard has an 'extension' which to date has ensured it stays on the right side of the mast. I have an adjustable kicking strap from boom to a block at the bottom of the  mast .The kickingstrap has prevented any flare-ups and also serves to 'pull' the sail across the mast when running. When gybing I try and haul the mainsheet in as much as possible to reduce the amount of loose sheet which sweeps across the cockpit and have done so  successfully in a variety of conditions.I believe a hoop across the cockpit is an essential safety feature to protect anyone in the cockpit.-having   said that  I admit I do regularly head butt it when not concentrating. All the rigging is as advised by Sunbird  Marine.

     
  • 04 Sep 2014 23:13
    Quote
    Reply # 3092712 on 1201045
    Anonymous member (Administrator)

    Graham, it is funny that your present vang doesn't work. If your boom is resting in a mast lift and with a tack parrel keeping it from moving forward, then a vang at 45- 50deg angle aft should give a decent kicking-strap effect. Sounds mysterious...

    Arne

    Last modified: 04 Sep 2014 23:13 | Anonymous member (Administrator)
  • 04 Sep 2014 23:04
    Quote
    Reply # 3092709 on 3092680
    Anonymous member
    Robert Burgess wrote:

    I read an article in a bulletin that written some years ago by Bunny Smith about what he had done to improve the windward performance on his sadler 26  whilst he had a forward raked mast, he credited a kicking strap for reducing the severity and incidents of gybes.  Have any of you any experience with a junk with a kicking strap?


    Your kicking strap is what Arne and I are calling a vang, I think.  The problem with most junk rig booms is that they are very light and you cannot set them up with a tackle as you would usually.  My boom kicked up in a partial accidental gybe recently in strong winds when the sail was reefed, despite the single-part vang being tensioned, though only hand tight. As I said in my earlier post, one problem is that the forward end of the boom is not attached to a gooseneck and can pivot down, reducing the effectiveness of the vang.  If the vang was further aft on the boom and tensioned with a multi-part purchase, like a real vang/kicking strap, it might be more effective but you'd have to have a stronger boom.  My friend, Gary Allen on the junk schooner, Grace Ellen, has fitted heavy booms and uses a 4 part tackle on the vang/kicking straps, which is what made me start thinking about heavier booms (see my post elsewhere on booms).  Gary uses the vangs to control sail shape to windward, because his sail has traditional camber and hinged battens, but I assume it helps in gybes as well.
    Last modified: 04 Sep 2014 23:06 | Anonymous member
  • 04 Sep 2014 23:03
    Quote
    Reply # 3092708 on 1201045
    Anonymous member (Administrator)

    Robert,
    If you bother with reading the note  here,  which started this last discussion, you will see that some use of a kicking strap (modified tack line) and a slightly beefed up boom is a part of the fan-up preventer which I describe there.

    Cheers, Arne 

    Last modified: 16 Jun 2017 22:18 | Anonymous member (Administrator)
  • 04 Sep 2014 22:10
    Quote
    Reply # 3092680 on 1201045
    Deleted user

    I read an article in a bulletin that written some years ago by Bunny Smith about what he had done to improve the windward performance on his sadler 26  whilst he had a forward raked mast, he credited a kicking strap for reducing the severity and incidents of gybes.  Have any of you any experience with a junk with a kicking strap?
  • 04 Sep 2014 12:42
    Quote
    Reply # 3092222 on 3092162
    Anonymous member
    Arne Kverneland wrote:

    Graham, to avoid the incidence you describe above, I think it is quite essential to have as little twist as possible in the sail when running before. Then, when a gybe occurs, the wind will gybe the whole sail from bottom to top simultaneously.  When doing planned long gybes, I turn the boat as fast as I can over the gybing point for the same reason.

    Arne

     


    Ah, most interesting, Arne. I do have a bit of twist in my sail, only having a standard six part, three sister-block sheeting system.  I can usually reduce some of the twist, after cleating the sheet, by hauling in on the top span and easing out the lower but it does not eliminate it.  Perhaps I will have to experiment with an anti-twist sheeting system such as the one you describe in your files.  I also think I will go for a heavier boom.  If I was going offshore I might make the boom the same size as the yard, so that if the worst came to the worst I'd have a spare yard, but that's another topic I should post elsewhere.
  • 04 Sep 2014 11:35
    Quote
    Reply # 3092162 on 1201045
    Anonymous member (Administrator)

    Graham, to avoid the incidence you describe above, I think it is quite essential to have as little twist as possible in the sail when running before. Then, when a gybe occurs, the wind will gybe the whole sail from bottom to top simultaneously.  When doing planned long gybes, I turn the boat as fast as I can over the gybing point for the same reason.

    Arne

     
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