That's some list of questions, Tony! But I did invite them.
Yes, I'll try to do some more pics, including (if I can) how the yard and luff parrels work. Action shots etc will have to wait until next season. Video? - good grief! The other thing I must do is to get my youngest to show me (again!) how to scan documents into the computer so that I can do some diagrams.
As this attempt to explain proceeds, I am very aware that it would be MUCH easier to demonstrate than it is to describe. I'll do my best...
Your other queries -
Down haul - under full sail, no down haul. I have a tack line which tethers the boom down, and the luff is tensioned against the up-pull of the halyard. When I reef, there is a downhaul for each of the bottom three battens: one on its own for the first batten, and a second one which cleverly does for both the second and third battens (NB any mentions of cleverness here and hereinafter refer to the innate cunning of the rig (down to the Chinese, essentially), not to yours truly). These tension the reefed panels downwards against the upward pull of the halyard.
If you let go of the sheet on a dead run, the sail would try to lie fore-and-aft and weather cock 'the wrong way round' (ie 180 degrees round from 'normal'). I think you would wring the masthead, halyard etc in the process. For this to happen, the sheet would have to unreeve itself through at least some of the blocks in the sheeting system or be bloomin' long! - it's long enough already. There are, of course, no shrouds to get in the way. It is, incidentally, acceptable to sail by the lee with junk rig, and gybing is less fraught - the sail somehow behaves with much more decorum. There is a (largely theoretical) potential catastrophe in JR sailing called 'fan-up'. This can occur when gybing in very strong winds, if the boom and lower battens try to go one way and the upper battens the other. There are some good drawings of this in 'Practical Junk Rig'. It could only happen if the clew can rise up a long way (boom up to 45% or more), and can be prevented by fitting a simple line below the boom, like a kicking strap but kept a bit slack. (Memo to self - fit one!!) Actually, fan-up can only occur anyway if one is sailing in 'adventurous' weather, say F6+.
In theory you could drop the sails down into the lazy jacks on any point of sail. There would be resistance from the lazy jack system itself, particularly on the lee side of the sail, and bear in mind that the commonest reason for dropping the sail, apart from furling, is to reef when, by definition, the wind is getting up. Best is to come up into the wind to reef (which is very quick anyway), but it's usually feasible to reef close hauled.
Cambers etc. This is territory where I accept that it is so because People Who Know tell me it is. My comments will probably get a B- at very best. The sail is like an aircraft wing on end, so that instead of vertical lift you get horizontal lift which is translated into forward motion by Wonderful Geometry which I scarcely understand. To get lift, you need an aerofoil shape, hence the need for camber. Slieve McGalliard talks about an optimum of somewhere around 15% camber: I take that to mean the max distance away from a straight line expressed as a percentage of the length of the aerofoil, so that's quite a lot. (There's also the vexed question of the point along the aerofoil at which this max camber should be). I think that one of the reasons a cambered panel battened sail is a good idea is that you have a stack of aerofoils, all under pretty close control because the back ends of the aerofoils, collectively the leach, are kept in line to the wind by the sheeting: thus they all work reasonably effectively. Contrast that with either a gaff or even bermudan sail, where the higher up the sail, and away from the direct control of the boom/sheet, the more the shape and direction of the aerofoil is different from the 'optimum' set in the lowest bit of the sail.
With immense and genuine respect, Tony, I'm not sure that received wisdom is quite as you describe, and if it is it partly reflects the inherent inefficiency of traditional sails. The flatter the luff, the closer you can get to the wind before the luff stalls, so in that sense you will sail closer, but the aerofoil behind that flat luff may not be very efficient in terms of (horizontal) lift. I think there is also some confusion, in strong wind situations, between on-wind efficiency on the one hand and being able to stall the sail easily (ie luff up) to avoid heeling on the other. In the process of the latter you sail closer, and if the wind is strong you may not be aware of the extent to which aerofoil efficiency is reduced - and it may not matter in the sense that the stronger wind 'gets you there' anyway.
I strongly suspect that most of what I have said is b*********cks, and if anyone wishes to SHOOT ME DOWN IN FLAMES (metaphorically speaking) with undiluted science, please feel free to do so.
Weight aloft - I don't think it need be an issue, with aluminium battens in particular. I think quite a lot
of modern JR yachts use aluminium for the yard as well. I've gone for CF mast for ease of stepping /unstepping and because I am getting doddery-er. I note that Robin Blain has done the same for his JR BC20. With the exception of the halyard and sheet which need to be normally chunky, all the running rigging can be quite lightweight because it is relatively unstressed. Fine dyneema is handy (eg for sheet spans). Most blocks can be correspondingly small, and I doubt whether there are many more of them than with other rigs. In a rig of the size of mine, small s/s thimbles can be used instead of blocks, especially making use of the inherent slippiness of dyneema (eg sheet spans again). So overall, no I don't think weight is a problem. It certainly isn't on my boat. However, for bigger than my tiddly rig, you should consult Robin Blain.
It may not have occurred to you, Tony, that your egging me on about all this JR stuff is helping me towards achieving 'hero' status on this forum. What an incentive! What an impending honour, to join such an elite! Almost makes up for my receding Olympic medal dreams.
Michael
