River Rat - a Bradwell 18 conversion to split junk

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  • 17 Sep 2018 09:12
    Reply # 6672407 on 6661896

    ... and if the wind had stayed at Force 2, I would have done much better!

    The light conditions really suited my small light boat. 

    I did have some rigging issues - you can see from my current avatar photo, taken during the race, that the sail wasn't raising to the top of the mast, which meant that the yard angle wasn't right, and the bottom panel didn't set, as I'd also been monkeying around with mast lift and lazy jacks.  I think the problem was the halyard twisting.  I have swivel blocks at the mast and on the yard; I think I should change these to non-swivel.

    Despite this, the boat sailed very well.  I was pointing at least as well as the bermudian boats at my end of the fleet, and kept up very well untill the wind decided to strengthen and go very gusty.  River Rat is quie tender, but felt very controllable.

    I finished 6th out of a field of 10 starters on handicap, in what was entirely a windward race.  I regard that as very respectable, considering I was only 18feet and single handed, and the others were mainly 30feet plus, fully crewed; and also I'd only had one weekend sailing with the new rig, so totally untuned.

    But more importantly, she turned heads.  Apart from her appearance (The Cat in The Hat was mentioned...), club members were very impressed with the way she performed.  As one member said to me afterwards  "I only know one thing about junk rig, or at least I thought I did, and that's that junk boats don't go to windward".  I think I shattered that particular illusion!

  • 15 Sep 2018 06:19
    Reply # 6670026 on 6661896

    I don't know about collecting "everything" together, but yes, I do realise I owe the editor a magazine article.  There's a few oddities about my approach.

    But not today - I'm sailing her in her first race under new rig.  Force 2 on the nose, so my hopes aren't high!

    Last modified: 17 Sep 2018 08:57 | Anonymous member
  • 13 Sep 2018 21:05
    Reply # 6668200 on 6661896
    Can you collect everything together and send it to the editor for a magazine article?  It all sounds like the sort of stuff people love to read, and only a small portion of the membership regularly uses the website.

    Or, at the very least, send some pics and up to 500 words to the webmaster so that you River Rat can be considered for a well-deserved Boat of the Month :-)

  • 13 Sep 2018 02:41
    Reply # 6667034 on 6661896

    Beautiful, James. Thanks for sharing. It felt like I was right there with you while reading.

  • 12 Sep 2018 21:30
    Reply # 6666708 on 6661896

    It sounds as if you are having fun, James. Well done.

    Luff telltales are a great help to get the best performance out of a rig which will let them work. Keep up the good work.

    Cheers, Slieve.

  • 11 Sep 2018 17:23
    Reply # 6664581 on 6661896

    Ah yes - that's it!  I must have seen that in my wanderings, in which case huge thanks for the method.  Your diagram explains the overall idea very well.

    It's my own character defect that made me need to start again from scratch, though obviously inspired by your method, and possibly also by the way hinged battens only approximate a curve.  Without your experience on how sailcloth takes up the shape, I plucked four out of the air as a number of tucks that felt good to me.

    Putting the tucks in was a bit fiddly, but not too bad.  For the main panels, I was putting in 37mm at the first corner, and 19mm (OK 2cm!) at the others. 

    The tucks are there, but not very big.  I didn't extend them a huge way into the body of the panels.  It would be easier to do that with fewer, larger, tucks.

    I will say that trying to get my head around what was happening in three dimensions was challenging at times!

  • 11 Sep 2018 17:08
    Reply # 6664533 on 6661896

    Prepare to be impressed - yes, I can make sense of your description! But however hard I look at the video, I can't spot the tucks. It's the method I recommend where the whole panel is to be made from one cloth, and broad seam is not available. The only difference is that I work out the shape graphically, not with your friend Pythagoras. However, I would only design in two tucks in a small sail, and three tucks in a larger sail. I suppose it depends on the weight of the cloth, but it can be hard to make a good job of narrow tucks in a heavy cloth. Fewer, broader tucks are easier.

    Last modified: 11 Sep 2018 17:11 | Anonymous member
  • 11 Sep 2018 16:42
    Reply # 6664509 on 6661896

    Yes, the jiblets are made with angled shelf foot, to Slieve's design.

    The main panels are a bit harder to explain.  I had some difficulties fully understanding what was going on with the various alternative methods, so devised my own, which is probably an exact reconstruction of a well-known technique!  I decided that the model for what I wanted to do was effectively an airfoil section above & below the panel (this is probably Arne's barrel cut method so far).  But two questions - one, how to know how much gather at each point along the batten, and the other, how to loft it when I didn't have enough space to lay out a single panel.

    So I took a leaf out of the broadseam method, and went for a construction that could be made broadseamed, but without the actual seams.  I've seen that idea somewhere on the JRA forums.  I looked at the airfoil section, and found four points where I could put in a tuck - at 2.5%, 7.5%, 20% and 40% along.  Using the NACA 0015 offsets, I could plot out where those points would be, allowing for 10% batten rise.  So now instead of a nice curved airfoil, it was approximated by five straight-line sections.  I needed to put in a tuck at each corner.  Pythagoras told me how much longer those sections were compared to the batten, so that's how much material to take in at the tucks overall. Eyeballing it, I reckoned that the change in tangent of the airfoil was approximately the same at the 7.5%, 20% and 40% points, so the amount to take in would be the same at those points, and double at the 2.5% point where the curve is greater.

    So my horribly complex spreadsheet eventually gave me cartesian coordinates along the sailcloth for all those corners, and told me how much tuck to put in at each corner.  Although the main panels are 244cm long (plus seam allowance) I was able to mark and cut out on a lofting board of 155cm x 61cm balanced on a plastic garden table.

    If you can make sense of that description, without any diagrams, I'll be somewhat impressed! 

  • 11 Sep 2018 11:56
    Reply # 6664005 on 6661896

    Very inspiring. I am still plucking up courage to make a sail like that, and hope to hear more about how you did it. I can see the "shelf foot" tailoring in the fore part of the sail, but no clue from the video clip as to how you put camber in the main part. Anyway, well done, and thanks for the post.

  • 11 Sep 2018 08:38
    Reply # 6663804 on 6661896

    Thanks for your kind thoughts.

    I'm a bit dry for photos at the moment, but a friend did catch me leaving the pontoon on Saturday.  Just three panels up, and not yet trimmed, but here you go.

    I can't get a good photo of the rig sailing, but here is a 13 second video clip with the full sail up.  If you look carefully, you can spot the unsheeted batten. 

    Last modified: 11 Sep 2018 08:57 | Anonymous member
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