Many thanks for your ideas. By lifting/flapping/fluttering I mean that instead of the luff and the adjacent part of the sail being taught and filled, it goes slack, same as if you point too high. With stronger winds this part of the sail flaps. The foresail is always perfect. My bolt rope is very stiff, but the main sail was attached with the rope so tight that there is some puckering of the cloth. I'll alter this first, but it's very interesting about the aspect ratio. I think single sail rigs would be faster than schooners etc. The thing that surprised me was the difference between the fore and main sails. There must be some interference of the airflow over the main by the foresail. This doesn't happen at low wind speeds, only at F4 and above. I've just done 500M dead against F4-6 winds so I've had time to observe!

Hi Alan,

Arion has a 7 panel sail with a distance of 1.22m between the parallel battens which are 4.6m long.  It is a reasonably high aspect ratio sail, with about 8% camber in the lower four panels, about 4% in the transitional panel and about 2% in the top two panels.  I have a 100mm tabling up the luff and leech, both of which were cut with slight hollows between the battens.  My luff shows no sign of lifting or flapping.  If I point too close to the wind, the cambered panel will shiver slightly (and boat speed drop off) but the luff itself remains taut. My luff is quite flat, the camber only appears further back in the panel and then disappears again by the time you get to the leech.  I'd probably choose a flattish sail for a boat that mostly cruises offshore but without a doubt, my sail sets well and is very powerful, especially against the wind in flattish seas (otherwise the fat little hull stops play!)

PS It's still much better than the flat sails. On an ocean passage against the wind in F4 and above I used to make 25nm made good. It's now 40nm!

Alan,

the difference between the sails you have and mine is that yours have a much higher aspect ratio (around 2.5?). In addition, on the only schooner (Samson) I have designed a JR for, I gave the foresail 10% camber, and the mainsail only  8%.

I can think of one or two possible reasons for your problem:

• The high AR leads to a very long batten distance (p). This makes the luff more vulnerable to flapping.

• A second possible reason could be that the boltrope has gone slack. Have you had this problem with the cambered sail from day one, or has it developed over time?

Arne

PS: If you by 'lifting' mean that the airflow from the close-hauled foresail blows into the mainsail, I guess the only remedy is to ease the sheet of the foresail a bit and point a bit lower. After all, a cambered junk sail is just another cambered sail, and this lifting in the mainsail of a Bm sloop is quite normal. I checked the drawing of Samson's sails. On both of them the max camber point is as far aft as 40% from the luff. This, in combination with the flatter 8% camber in the main could be the reason why his mainsail does not lift. Another reason could be that the owner does not point his ship that close to the wind.

PPS: Have you tried some sort of downhaul to keep the luff of the main taut?