It seems to me that the aim should be to have battens that are strong enough to allow the boat to be driven hard, and to survive squalls, no matter what type of hull you have.  Once you have achieved this, then it is just a matter of reducing sail area, whether on or off the wind, to keep control of the vessel, and this will indeed depend on hull type.

They all have their advantages.  I've surfed downwind for long periods in light-displacement boats, which was huge fun.  They were easy to steer, but required constant attention to the helm. Displacement hulls obviously won't surf, and if you drive them too hard, are liable to broach, whereupon you may well start breaking things.

The displacement hull is easier set up for self-steering in my opinion, but there are always exceptions to the rule.  People do use autopilots successfully when surfing downwind on light boats, but if the autopilot fails on the face of a large wave, chaos may ensue.  A few of the round-the-world racing yachts have capsized when their autopilots broke while surfing.  I would not choose a light-displacement flyer for solo ocean cruising, but others have.  John Guzzwell's Trekka was light, and he surfed at times.  More recently, Webb Chiles circumnavigated solo in his light-displacement Moore 24, Gannet, regularly replacing autopilots along the way, and says it is the best offshore yacht he has ever owned.

I drove my 24' (7.3m), 5-ton, junk sloop, Arion, very hard downwind.  We were never likely to surf, but surged on the crests of waves for long periods at times.  That boat never showed any sign of broaching, even under its previous bermudan rig.  With the junk rig, I eased the sheet right out until the upper sheeted batten was athwartships, and the unsheeted batten above it, plus the yard, were beyond athwartships.

How you sail your boat will depend on many factors, including design and personal preferences, but the yard and battens should be stout enough not to break except under exceptional circumstances.  It should not be determined by the amount of sail you carry.  The only consideration for reducing sail should be the control of the vessel.  It will also depend on the sort of cruising you do.  For inshore or coastal cruising, I'm quite happy to drive the boat hard, but for offshore passages I subscribe to Roger Taylor's philosophy of easing along.

Paul S wrote at 31th May:

As for tacking angle in light winds, there are two possible reasons for that:

• Tacking angle on the chart will always be worse in light winds than in strong winds, since the headwind (boat speed) component is relatively stronger than in stronger winds. We don't sail twice as fast in 12kts winds as in 6kts.
• Some fine keels may lose grip in lighter winds. My former boat, Johanna was not so good in that respect.

Arne

 Ah, this is not what I meant. I mean sailing with too less sail area for a given wind, i.e. reefeing too much and thus being "too" slow.

This is after all not rocket science.

As you reef the sail, the mast and the boat’s superstructure will still be there in full size to produce parasitic wind drag. Thus, the speed to windward will drop, and the pointing angle will be wider and wider the smaller sail you set.

To give an idea of how much wind drag there is in the boat and rig, drop the whole sail in a good breeze, and then measure your downwind speed. You will be surprised...

Arne

Paul wrote:

I have been warned, that one shall reef early when running, as there would be a danger of "batten breaking". However, I don't quite understand, if for example I lower two panels, why the battens of the upper panels should then have less load... Sure, with two panels down the boom and lower two battens have way less load. But this does not affect the upper ones, does it?

Paul,
Your logical thinking about this is good, but there is another factor (or two). When I deep-reef my sails, the lee topping lift appears to support the yard and the remaining battens at work. Therefore, it appears to me that these see little load, even in a strong blow (photo). Of course, it depends on how the lazyjacks are arranged. I use a pair of stout, nearly straight topping lifts and then just add (non-structural) sail catcher to these.

Arne

PS: another reason for warning against driving hard with the sail squared out, is that the battens see increased compression load in this position. This may make wooden battens snap almost without warning. Aluminium battens bend more under load, and give you a discrete hint...

PPS: yes, and the two top battens are stouter than the others...

(see my member's album, photo section 8, photo 20)

I find that one of the unusual aspects of sailing junk rig, rather than gaff or bermudian, is that I tend to reef when I turn off the wind and shake the reefs out as I sail closer to the wind.  

You might still be in the mindset where shaking out the reef as the wind comes forward of the beam is the opposite of what feels right.  When in doubt, shake it out: it's easier enough to put back in if you've been too enthusiastic!

As for tacking angle in light winds, there are two possible reasons for that:

• Tacking angle on the chart will always be worse in light winds than in strong winds, since the headwind (boat speed) component is relatively stronger than in stronger winds. We don't sail twice as fast in 12kts winds as in 6kts.
• Some fine keels may lose grip in lighter winds. My former boat, Johanna was not so good in that respect.

Arne

 Ah, this is not what I meant. I mean sailing with too less sail area for a given wind, i.e. reefeing too much and thus being "too" slow.