Stacking the battens

Eric.
Hasler and McLeod focused quite a lot on this ‘batten stagger’  issue in PJR. With their standard sailplans with equal length battens, each panel was shaped so that the diagonal between the panel’s clew and its throat corner came out a bit shorter (50mm or so) than the sail along the battens below. This was to prevent any sheet-batten tangle when hoisting sail.
This worked just fine on my first flat sail on my Malena, even after I modified it with hinged battens.

Not so with baggy panels. I only noticed this in earnest when sailing Johanna for the first time. When the first reef was taken, the clew end of the boom ended up protruding about 20cm aft of the leech. More reefing went well as the batten parrels prevented the sail from moving further forward.
Even so, when hoisting sail, I had to bring the sheet bundle to the right side of the boom before starting hoisting the sail.
My simple horse-cure to the problem was to cut 25cm off the boom at the clew and then cut off  (wrapped, really) the clew of the lowest panel.

This practice has been adopted for all my sails after Johanna’s.
My present Ingeborg is a special case. I didn’t get the position of the CE right  in the first place, resulting in too much weather helm. The quick fix was to shift the sail forward, almost as far as the shortish batten parrels allowed. As a result, when dropping the first panel, the sail cannot shift forward, and the rest of the battens stack nicely (..well...) on top of each other.

This is shown on the photo below, taken yesterday, actually.

I reckon that this method, with shortened boom and shortish batten parrels works well enough on this sort of sail.

Arne

PS: Disregard the protruding boom. I don't remember now, but I probably cut it to the same length as most battens at 5.00m

Anonymous wrote:

The reason for angled battens is to keep the leach end of the sail out of the water when the boat rolls in a seaway, without having to hoist the sail to far above the deck. It also keeps the sail above the crews heads....  Boats that don't have to go off shore can likely have the battens at any angle they may care to have them.

Lastly, the surface of the water is a chaotic interface between the two mediums that has high turbulence, something our small boats cannot escape. I can see no reason to assume that the airflow is always parallel to the surface of the water. Likely it is anything but that.

There is an other explanation that I found in "Practical Junk rig".

In Chapter 2 : the geometry of the sail, it is explained that the battens had to have positive stagger in order to prevent the sheeting to be catch in the reefed sailed burden.

With the deck configuration of Jester it was essential to prevent the sheet system to foul .

As often the reason has been forgotten but the pratice is maintained.

With positive stagger, the sails is moving backwords while reefing mooving the geometrical sail center backwards when the sail is reefed. Aparently it doesn't create too much weather helm.

The triangular top panels have the same effect to move the sail center backwards.

If you have no stagger, you don't need anymore a yard parrel as the yard will stay longitudinally at the same place in regard to the mast. It should be possible to use a  traveller (?)- rocambeau in French- (A iron ring with a hook that runs along the mast on gaff sails).

On Mingming's wingsail, as I need a double sheeting sytem, I choosed to have no stagger at all. Trials will tell if it works...

Eric

Paul T., thank you for your excellent explanation! 

Some thoughts to...

... not wanting to touch neither the crews head nor the water when heeling: Wouldn't it be sufficient to only design the boom at such an angle, but use a more "airflow friendly" for the rest of the battens? Hypothetical, extreme example: boomrise angle at 12° for enough clearance, and batten angle at 6° for the sake of less drag. That would surely be an unfamiliar sight of a junk rig - for now I'm only brainstorming here :)

... chaotic airflow at sea. I understand your point, there will always be lots of change between more upwardy and more downwardy flow. No argue on this one. But the average of that chaos can only be parallel to the (calm) sea level - and wouldn't it make sense if the rig aligns at least with the average wind direction?

What do you think?

Cheers

Paul

Paul it is hard to determine where the wind is blowing from on your track, but of possible directions it indeed looks much better than I anticipated.

What I did mean in my last post is, that I understand your sketch as seen from behind and the wind coming in from the side.  Maybe you died not mean that? In that case for the Bermuda the flow over the top has negligible influence, since than only the apparent wind coming in from the front has any driving force.  If you meant the wind coming  in from behind (but why then should the sail heel?) The Bermuda has very poor results compared to a square sail, if not only for the small area exposed. I think what confuses is you showing wind going over the top when you probably did mean the boats are sailing upwind.

(Had to take a little break)

Regarding the battens of the junk, it seems to me that when they angle upward behind, they form the "nose" of an aerofoil and creating the turbulent vacuum behind. Higher up the angle is bigger, meaning the batten is more vertical and so coming closer to a full "aerofoil" with following bigger results.

That is OK. I would remark that with a Bermuda the wind flow over the top would not do anything in this situation since the camber is vertical and the drive comes from the low pressure after the camber. Since I have read that the junk rig performs poor in windward situations I can see how it works downwind. What I think is because of the many cambers you get firstly an increase in sail area and in addition a more complex vortex pattern which might possibly increases the vacuum on top of that.

Edit:

could it be that a vertical camber is formed at each panel in the front?