Vo and Oana of Madam Wong took this interesting photo of Arion recently (among others).  Click on the image for the full-sized photo.

It clearly shows how the short yard allows the top, unsheeted batten to fall outwards, creating a distinct cambered shape to the top fanned panels.  20mm of broadseaming in the top three panels also contributes a little to the shape.  The overall effect is that the top panels, like a gaffer's topsail, are very powerful and really get the boat moving.  In flat water I can ghost with steerage way when one can scarcely feel the breeze across the deck.

During my next summer layover (yes us tropical sailors lay over in the summer and cruise in the winter!), I am going to put double-cone hinges in the lower two or three battens and set the sail loose footed (only the tack and clew attached to my over-strong boom) which should give me a nice cambered sail, with the camber reducing as you go up the sail, or reef, giving me a full sail for light winds and a flattish one for strong breezes.

Scott Dufour wrote:

Graham,

I looked but probably missed it in the post - how much hollow (% of vertical panel length) did you put into the leach to get this flat aft effect?  Was it a catenary or was that not necessary?

I didn't quantify it, which is why you missed it, Scott.  There is 100mm of hollow in panels that are 1200mm wide, which according to my calculation is 8.33%.  I asked my sailmaker to put in some hollow, to avoid fluttering, as my spare sail, which has a straight leach and a light tabling (unlike Arne's webbing "boltrope") flutters badly in fresh winds.  The sailmaker, Ian Markovitch, of Redhead sails in NSW, is a former world-champion Paper Tiger catamaran sailor, who came 5th last year at the age of 70 in the Australian National Titles.  His racing sails have a reputation for being very fast and unbreakable.  In his youth, he did a long voyage in a 16ft open boat, and had also read Practical Junk Rig, so I decided he was the perfect sailmaker for my project.  We had a lot of discussion when designing the details.  His argument for a larger than usual hollow was to counteract the scalloping effect of a junk sail, given that it just hangs off its halyard and does not have the luff cranked up tight like a bermudian sail.  A webbing boltrope would have stopped flutter too, but the large hollow gives a superior set to the panels.  I didn't realize it would create some slight  camber in the panels, but Ian probably did.   It is a wonderful sail.

Arne Kverneland wrote:

Good, Graham.

Another question: What has been done to prevent the luff and leech from stretching?

I ask because if stretch of the luff or leech is eliminated, then any stretch in the canvas will lead to a little bagginess, or camber...

Arne

Hi Arne.  The leach has a very heavy tabling, 4 layers of 7oz Dacron.  The first 2 layers are  300mm wide, and the top 2 layers are 150mm wide.  That's 5 layers including the sail.  Triple stitched.  The luff tabling has 2 layers, 150mm wide, (plus sail), also triple stitched.  The cloth of the tabling was cut with a vertical orientation.  I don't think it can stretch much, if at all.  Like all flat-cut junk sails, the battens lift slightly, especially since my tack line is always slack, causing the panels to scallop slightly.  But the deeply hollowed leach between battens pulls the back of each panel completely flat, like an ironing board, then it gradually eases into a bit of belly, before coming in again at the straight-cut luff, but not as much as at the leach.  This results in a slight curve from luff to leach, with the maximum belly well forward of the middle.  It's not much, couldn't be more than 1%, and the shape of the fan, which twists off like the head of a Reddish sail, probably provides most of the drive.  It's just a fluke it performs so well, but I'm delighted.  I was willing to trade performance for simplicity, given my sailing style (mostly downwind cruising) but don't seem to have lost much after all.  A sail with 6-8% camber would have a lot more power to windward, but Arion complains bitterly if I try to sail too close to the wind in the open sea. (And so does the skipper.)

Arne Kverneland wrote:

Graham,

could I suggest that you fit a telltale at the leech of each batten panel?  If you can make them stream aft, then there must at least be enough camber to establish some attached airflow on the leeside of the sail. In that case, you should expect some improved performance over a dead flat sail.

Arne

Thanks, Arne.  I recently took an old JRA member, Gordon Evans, for a sail on Arion and he suggested the same thing.  He sails a Sabot dinghy with junk rig and uses telltales on it.  He was impressed with the shape of my new sail and confirmed that the flat-cut panels actually develop some camber due the the cut of the leach.  I had been wondering if it was just wishful thinking!

Yes, it is pretty rough sailing against the trades, especially inside the Great Barrier Reefs, where the shallow water makes the seas short and steep.  If I can average 2-3 knots to windward, I do 4-5 knots on a run, and in fresher winds, when I am averaging 3-4 knots to windward, Arion sits happily on 5-6 knots homeward bound.  So my speed to windward is half that of downwind averages, but of course I am tacking through 90 to 100 degrees, so sailing a lot further through the water when outward bound.  Even with my bermudian rig, I didn't do much better to windward (and was slower downwind!). 

I'm happy with my new sail but I'm still a fan of camber.  I chose a flat-cut sail because I mostly sail downwind and also because it was easier to get a professional sailmaker to build it.  My spare sail is also flat cut and sets as flat as a board.  I've sailed with it last summer while waiting for my new sail, and once before while waiting for the black sail to arrive.  It had very modest windward performance and Arion was often difficult to tack.  The new sail has surprised me with its power to windward and it has to be attributed to the shape it presents to the wind, ie camber, albeit not very much.

If I build another sail I will probably try and put a modest amount of camber in it, but it won't be made out of black Odyssey material that's for sure.  I like Dacron, despite the need for sailcovers, however Topgun has served mehitabel well for more than 10 years without sailcovers, which is impressive.  It may be some time, if ever, before I need to replace my new sail.  I am just mooching along the east coast of Aus, due to ongoing health issues, and have the sailcover on 80% of the time.