Please visit our other sites at www.TriloBoats.com and TriloBoats.blogspot.com for plans, background and focused discussion.

21 January 2014

Rig o' Morale

Split Junk Rig Ketch
Rigging Approximate

Still, no one goes 'down to the sea in their proud simulators!'
From Down Periscope


Rig o' Morale

One of the downsides of sailing in SE Alaska is that its kinda lonely, cruiser-wise.

Despite numerous friends from many walks of life, our sailing friends are few and far between. One consequence is falling behind the times.

Our beloved junk rig has undergone some changes in the last couple of decades we've 'been away'.

First, Arne Kverneland's experience and writings inspired many to build camber (airfoil shape) into junk sail panels. Camber allows the ususally flat-cut junk rig - notoriously 'inefficient' to windward, though comparable to most workboats from the age of sail - to overtake the mid-range of bermudan rigged racer-cruisers.


Steve McGalliard's POPPY under SJR
Second, Slieve McGallister developed the Split Junk Rig (I'll call it SJR, from here on out). Fully cambered, it divides the fore area (called the 'balance' in junk and lug rig... the small sections are called 'jiblets' in SJR) from the main, aft area at roughly 1:2 by a narrow slot along the mast. This reduces turbulence at the mast and keeps it from cutting the camber. Some slot effect may be generated, as well.

To assess the rig, Slieve has been racing POPPY, a middle aged cruiser, against the big boys and girls of Great Britain. And finishing in the top 10% in a field of hundreds!

In other words, a sail with all the advantages of junk rig has achieved excellent windward performance!

Of course, one can't just run with a successful formula...

The rig Anke and I are likely to mount puts a crab-claw panel up top - we like its behavior as the last sail standing. The next panel down is 'transitional' purely for vanity... we like the looks. The rest drops straight down like venetian blinds. The leech has been slanted, a bit, to provide positive, aft 'stagger' (overlap) so the sheets don't foul one another.

That crab-claw serves another function... coming to a universal (rope) joint at the forward apex, the lower 'limb' acts as a strut to the yard. Normally, the pull of the halyard high on the yard would depress its forward end, spoiling sail shape. But with the strut, it's position fixed at the mast by a rope hoop, prevents it from dropping and therefore forcing the aft end up (good for sail set). This eliminates a 'yard hauling parrel' (don't ask), leaving one halyard and one sheet per sail.

Playing with someone else's genius calls for caution... we built a scale model (1:6), which works perfectly. But proof will be in the field, if anywhere. As far as I'm aware, it will be the first, full-size multi-masted rig with two SJR sails.

So we get to mount a LOT of sail on masts of manageable height, each with good bury (support). The foresail provides beautiful balance on and off the wind (without adjusting position), and the aft sail is in good position to manipulate the stern via backwinding. SJR helps fill the space over the big mid-deck without introducing long-boom weather helm.

The layout shown is a big rig totalling roughly 800ft2 (57m2). Both are extremely powerful, so we'll have a learning curve, especially since each sail generates power toward the ends of the hull. We may find ourselves accelerating into abrupt turns until we get the hang of things.

But junk rig is docile, and the large balance of both sails makes it even more so than usual. Speed generally gives good control. But we'll start slow and small, just to be sure!

And the payoff may be some true, windward sailing; not just the plodding we're used to. Our flat-cut sails have surprised more than a few folks on the water; these may astound!

Fire up them morale boosters, Matey!

9 comments:

  1. Nice choice on the SJ! I made a polytarp version for my dinghy and it is a rocket downwind. Upwind speed is good too, but I'll have to move the mast step farther aft to tack (kind of expected that though). I look forward to seeing your version.

    ReplyDelete
    Replies
    1. Hi Jeremy,

      We're excited, especially by the promise of increased windward ability (off the wind, JR is plenty adequate for our needs).

      Based on your experience, what do you think of that crabclaw/strut upper panel? Any objections leap to mind?

      Dave Z

      Dave Z

      Delete
    2. No objections whatsoever. In fact I might have to try it myself. I really like the strut eliminating the YHP. I've looked at some convoluted arrangements running to blocks fixed to the first batten, but your design is much cleaner.

      I won't say much for my experience. I made the sail over the winter last year, then suspended the project to do a bunch of work on the "real boat". I only got one test sail in at the end of the season, but that was enough for me to fall in love with the rig.

      As for the claws, I could speculate on effect of CE when reefed or tip vortices but I have no clue about that stuff. What I do know is: they look fantastic.

      Maybe I'll have to do a post on my rig. Some "don't do it like this" material there.

      Cheers,

      Jeremy

      Delete
    3. Hi Jeremy,

      We used the crabclaw upper panel on SLACKTIDE, but without the strut.

      It has behaved VERY well as a last sail... two of them drove the barge hull to windward in about 45kts sustained. The deep hollowed leech moves the CE forward/inboard, reducing weather helm, The greater SJR balance should be better yet.

      And yeah, we love the looks!

      Dave Z

      Delete
  2. Hi Dave,

    That's looking really interesting – fascinating article by Slieve. Question: is your ratio of 2:1, aft of the mast:forward of the mast horizontal dimension of sail, because you have two masts? In the photos in Slieve's article, the proportion looks more like something in the neighborhood of 3 or 4:1. Just curious!

    Still looking at the Reddish rig for AUKLET, because of the short mast situation. But it does make one fantasize about a taller mast in the future…

    Shemaya

    ReplyDelete
    Replies
    1. Hi Shemaya,

      Slieve's rig, shown above, was an early implementation that is indeed 25% balance (3:1 sail). Based on his experience he writes that 33% to 35% balance is preferable, being stable with reduced sheeting loads and weather helm.

      While it's aspect ratio (height to width) is recommended at 1.6 to 1.65, the vertical leech means that the aspect ratio falls as the sail is reefed. The Reddish Rig, in terms of aspect ratio, is similar to an SJR with two reefs in. If you implemented SJR on a shorter mast, I'm guessing you'll still have improved windward performance over an equivalent RR, but with a sail that's much easier to handle.

      All this is speculative on my part to date, however... I'd love to get a little fleet of PDR folks together and race various approaches against one another.

      May the best rig win!

      Dave Z

      Delete
    2. Hmm... reading over my answer, I note that I'm falling once again into the 'best is fastest' trap. 'Best' is actually the best fit to the needs of the owner, in my book.

      So again, we're prizing the inherent, large balance of the SJR (works well at 25% and seems to improve up to 35%), and possibly trading off speed under deep reef for crab-claw set, geometric and handling qualities.

      The latter may degrade speed, possibly on all points, but we value other aspects enough to take that risk.

      DZ

      Delete
  3. I've been meaning to write this up for a while. Thanks for the kick in the pants.

    http://jeremyulstad.com/2014/01/split_junk_part1.html

    ReplyDelete
    Replies
    1. Hi Jeremy,

      REALLY like your modified Agile Boatbuilding concept. Great write up, too.

      That GDA (GeoDesic Aerolite) looks like an agile platform for tryouts.

      One point I'd add is that a critical function of the jiblets is to blunt the leading edge of the airfoil to (I recall... Better check me) an efficient 9deg. A problem for fully cambered panels has been too sharp a leading edge.

      Dave Z

      Delete

About Me

My photo
Anke and I live aboard SLACKTIDE, our T26x7 ketch. We sail by wind, tide and muscle in the waters of mid- to northern Southeast Alaska. We try to maximize the joys of life, and minimize the chores. ........ We live between the communities of SE Alaska, but drop in to visit with friends. Lately, we've worked, every other winter, care-taking Baranof Wilderness Lodge in Warmsprings Bay. This has given us a window on Web. ........ We're working toward a subsistence lifestyle, somewhat impeded by addictions to coffee, chocolate and cheese. ........ We think TEOTWAWKI is looming, and while we won't be ready, we'd at least like comfortable seats.