Kurt Jon Ulmer wrote:Arne & David,

But gentlemen, they are not flat - they are Flat Enough.

Kurt

Dear Kurt, When I look at your photos of mehitabel's sails I get a peculiar feeling.  My psychiatrist tells me I am suffering from an acute case of panel envy.  Your sails looks so predictable.  My sail is a bit like Jim Carrey's face, it can do wonderful things, but you never know what it is going to look like next time.  Or more to the point what it is going to do.  I have tamed it with Arne's throat hauling parrel but it needs to be tamed every time I lower it.  Once it is up it sets very nicely and sails like a witch.  Sometimes, when hoisting it in a swell and it is not restrained by the yard hauling and throat parrels, it flops all over the place, within the restraints of its fixed parrels.  Perhaps if I had it set up like Arne's sail, with a full length yard, a vertical or possibly aft raking mast, short fixed batten parrels, a shortened boom and rubber hose extensions on the leech end of the battens to hold out the sheetlets, then I might become confident enough to sail with this sail at night.  Right now, it is strictly a daysailing rig.  But, oh, what a wonderful daysailing rig it is too.  Arion is turbo charged, possibly sailing better that I did under the bermudian rig. I only had a working jib on a roller furler and my cambered sail gives a performance equivalent to a genoa I think.  I am not very good with engines so I do like a rig that performs.  But I also need a rig that I can handle with confidence on a dark, windy, squally night, when what keeps you safe is gear you know and trust.  I cannot see this sail ever passing that test but I am still working on it.  The flat Dacron sail I have has four fanned panels in the head which do give some camber, and the bottom two panels are in the form of a separate bonnet.  I could build a bonnet with camber which will give me some light air performance.  Once I have reefed the first two panels I will be back to a flat sail for heavy weather.  This sail would be very similar to a flattish Fantail sail which I suspect offers the best compromise for offshore boats.  If I had a bigger boat that needed a split rig, I would make it a schooner, with a large Fantail mainsail and a smallish, more conventional foresail, with flatish panels of course.  I love the look of my black sail and am not planning to remove it just yet, it's just that, when I look at mehitabel I get this strange feeling, kind of painful but pleasant, it's confusing...

Gary King wrote:Graham, there's a Tom Thumb file in the "your files" section which I assumed is the plan for your bottom panels, which I looked at because I'm using the same tuck method for our panels. Anyway, the particular panel drawing in question would give a camber 334mm or 7.4% (using Arnes formula). 

Arion seems to be able to sail up the wall with that camber so I'd be happy with it.

That's very interesting Gary. Yes that drawing is the one that was used by my sailmaker as far as I know.  My understanding was that the bottom 4 panels were only to have 184mm camber, which is 4%. It certainly looks more like 8%, and yes it does seem to suit the boat.  Serendipity.  I am happy with the sail for my current purposes, sailing inshore, but if I ever go offshore again (which is uncertain because of my health) I would want to reduce it, or build a new flatish sail, or more likely just bend on the flat Dacron sail I carry as a spare.

I have just added four new photos to my first member album of Arion sailing which may be of interest.  The first two show the sail while beating to windward at sea without Hong Kong parrels and one in particular shows the amount of camber in the sail, which seems, upon reflection, to be more than 4%.  I have not measured it yet (I will soon).  Whatever it may be, for inshore sailing at least it produces a very powerful sail as the third picture demonstrates very well.  This photo was taken by Andrew Bray, father of Chris Bray of NW Passage fame.  Andrew and his wife Vicky are sailing around Australia on their aluminium cutter, Starship (which Chris circumnavigated on as a boy), and they are spending the cyclone season in Cairns.  I am hoping to catch up with Chris next week when he visits for a few days.  Andrew took this photo as I was tacking through the anchorage, zig zagging among the moorings like an overblown dinghy.  It created quite a stir - lots of people on deck, some with cameras, others watching anxiously.  I think they were all a bit shocked that a junk rigged boat could perform like this.  Andrew said afterwards that he assumed i had my engine on until I sailed across his stern.  Arion has always been fast and close winded in flat water (at sea I need to crack off to keep the fat, heavy hull moving), but I seldom sailed singlehanded through the fleet like this under bermudian rig, as it was too much work tending the jib sheets and keeping watch.  Now all I have to do is calmly put the tiller down and hand over the mainsheet, which has fallen in love with my wind vane and tries to embrace it at every opportunity.  The boat also accelerates rapidly out of each tack and tacks through less than 90 degrees.  That allows me to sail a lot closer to other boats and make longer tacks.  The sail looks a bit messy (its shape is very dependent on the tension applied to the running parrels and I am a lazy sailor) but that does not seem to detract from its performance.

Arne Kverneland wrote:

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                                                               Stavanger, Friday

Graham, I bet that some of the negative-stagger problems you got when changing to cambered panels stems from the forward-raking mast. With the mast raking forward, the mast top, where the halyard goes, will be well forward of the base. Ergo increased negative batten stagger when reefing. Conversely, with an aft-raking mast any tendency to negative batten stagger will be more or less reduced.

When watching photos of Chinese junks, I never find main or mizzen masts with forward rake, only on some (not all) fore masts. Quite the contrary; several main and mizzen masts can be seen with a slight aft rake.

Quote from Brian Platt:

All the masts have a forward rake which, with the high poop, give the vessel the appearance of "slipping downhill". This creates the impression that the junk would bury her bows in a head sea, but I found it to be quite illusory. Some helicopters create the same impression that they are flying into the ground! The reason for the forward rake of the masts is probably to cause the sails to swing outboard in light winds. The rake of the foremast is much more pronounced than that of the others. Acting half as a mast, half as a bowsprit, it increases the sail area and brings the centre of effort forward. Another effect is to cause the foresail to "goosewing" of its own accord when running before the wind.

You know what they say, Arne: "Never say 'never'"! ;-0

Gary King wrote:Just compared the theoretical camber between Zebedee's and ours using the numbers Alan supplied. Using Arne's new formula  (R=0.55 x camber),  Zebedee's would be 9.1% versus ours of 8.7%. Little too baggy for comfort.

Yes David, I have slight concave in the aft curves, tabling only on the leech (no bolt rope planned), and may add webbing to the luff though (on top of tabling).

                                                                Stavanger, Saturday

Gary, even with cutting the panels with dead straight round the last 40% I have also noticed a slight convex curve in the resulting camber, but I wouldn’t call it a hooked leech, so I don’t think it is such a big deal. Still the use of a bit concave rounding to straighten the aft part of the camber sounds very interesting. I guess I will have to make a full size test panel and take it out for a dry-sail before sewing up a sail for my new boat.

However, I fear that it is easy to overdo this concave curve. I once saw photos of the schooner Taz, owned by De Clarke, and there the camber appeared to go negative in the aft part.

Regarding tabling and webbing; as I see it, the leech is under harder strain than the luff, in particular if the throat h. parrel is being used (which off-loads the luff a good deal).

Arne