David,

Comparing your mk1 Weaverbird rig to Annie’s I see that there are quite a few subtle differences.  (Please correct me if I am not right.)

• Higher aspect ratio.
• Hinge point.  Annie’s seems a long way aft.  Though I recall you may have had two hinges.
• Tapered panels.  Yours don’t change that much from the ones below.  Annie’s much more so.  
• The hinge point on Annie’s top panel is proportionally further aft.
• Annie has a concave luff, yours looks straight.

It would be good to hear your comments, and of course Annie’s. 

My uneducated thought, would it help if the top panels were not tapered, just shorter?  Accepted it would not look so pretty.

(Should this be a separate thread?)

Discussion in a circle...

This sort of discussion around the cambered panel sails seems to erupt on irregular basis since the first JRA rally in Stavanger, back in 2004 (See JRA Mag #44). It mostly goes in ring: The cambered Stavanger sails started with being regarded as very baggy (8%)  -  and probably unfit for offshore work. Later, when they started up in New Zealand, and Paul Thompson rigged his La Chica with 10 and 12% camber, the camber of my sails suddenly moved back to being normal and even ‘moderate’ (“Hooray, I am normal!”). Now my sails again seem to move up in the very baggy league  -  still with the same 8% camber.

Stress in the sailcloth of a cambered panel sail.
I like to think of the sailcloth I use as being very weak, just as the original Chinese cloth. Instead of beefing it up in the corners, as western sailmakers tend to do, I let the stiff battens, the boltrope, and the Hong Kong parrels act as a stiff frame. This frees the sailcloth from doing any other job than catching the wind and transferring the force from each panel to the surrounding battens and boltropes. Job done. My baggy sails, with no patches anywhere, have proved to work well and last well.

Stress in the yard, battens and boom.
When shifting from a flat to a cambered sail in Malena (See NL30), I didn’t anticipate the increased load on the yard, but it proved to be strong enough anyway. Later, with bigger sails, I had to make that yard stronger, in particular in the vertical plane. The longer batten 2 (from top) on Johanna also needed to be made stronger than the others. In Johanna’s rig the THP and YHP also was under quite some load. This has been solved on my last two rigs (Frøken Sørensen and Ingeborg), by increasing halyard drift, shifting the halyard 5% aft of the middle of the yard, and the YHP 2/3 up the yard. Small, simple changes resulting in much reduced tension in the THP and YHP.

The flat-topped, high-balance sails that many use now, have most probably even lighter loads on the control lines than mine, in particular the SJR. Slieve’s alternative to HK parrels are his very clever batten parrels cum downhauls  -  a real Columbie Egg. Still, my THP and YHP are not anywhere near needing a winch or extra purchase these days, just a moderate tug. In addition, I don’t touch them when under way.

I wish I could bust this myth about the high stress in the ‘high-peaked’ Johanna sails. Anyway, I stick to it, as it gives the tallest sail on the shortest mast. Handling the stress  -  both in the mast and in the moving bits  -  is a simple matter of engineering.

Arne

Oh dear, it is not desirable to get involved in these rig design discussions but when misleading information is being offered then it seems a good idea to try to correct a few points.

This all started because Annie reported a structural failure in her rig in what would appear to be in relatively benign conditions and on a fairly low stressed point of sail which should not raise problems in a well found rig.

Looking at the posts so far Arne has made the point that by taking some elements of his cambered rig design but not following all the elements then it is probably that the resultant rig will not replicate the consistent performance that his rig achieves. David Tyler states, “The SJR also offers high performance with low stress. It gets it in a different way, but there is still this commonality with my rig: low yard angle, no HPs, just downhauls, and panels that are not so extremely baggy as yours”. This would appear to be suggesting that the SJR is copying from his rig. The expression, “Cart before the horse” comes to mind as initially DT heavily criticized the SJR and it is only in recent years that he has started to adopt the low yard angle downhaul features, but as Arne has commented above, David has not included all the features required to make it a low stress rig.

In the article 'Some Thoughts' I pointed out that to reduce the stresses in a rig any taper or change of angle of the leeches between panels should be balanced by an equivalent change of angle between the luffs panels. As drawn for Annie's SibLim, the rig has a straight luff from Yard to bottom batten/ boom but has taper in the chord of the top three panels. This means that luff haul parrels are required to push the top battens back against the forward thrust of the leech which places the battens under compression even before there is any wind pressure in the sail. The rig does not simply hang stress free in shape from the halyard as the SJR does.

Marconi found it necessary to provide stays and spreaders to keep his tall masts in column to prevent bending under the gravitational compression loads, but with battens we do not have that luxury. To withstand compression loads the battens should ideally be kept dead straight and be of a stiff light material. The SibLim rig has hinges in the battens which A) allow the battens to get out of column over their length and therefore suffer bending loads, and B) concentrates these bending loads at high stress points such as the ends of the tubes at the hinges, or the ends of the joining cones in the hinges.

Unless particularly strongly engineered the battens in the tapered panels with the enforced straight luff are vulnerable to failure, and it would appear that that is what has happened in Annie's case. Hinges battens will always have this weakness when under compression loads, and it is easy to see why Arne stopped using them as soon as he had found another method of introducing the camber required to get respectable performance out of a junk rig.

A structurally sound junk rig with a torn sail can continue to sail, but a sound sail with a broken structure could be a death trap.

Voyages have been successfully made with hinges battens, but that does not make them safe. It does not make sense to push your luck and set out with a rig with known weak structural features when the same or better performance can be obtained from rigs with simpler and stronger setups.

Thank goodness that Annie is an experienced sailor, but even so she found it desirable to resort to engine assistance to get into a safe haven. A less experienced sailor might have made bad press for the JRA if presented with the same situation.

By the way, the SJR may be thought to be less 'baggy' than Arne's rig, but aerodynamically it is probably more baggy.

Cheers, Slieve.

Anonymous wrote:

Martin having succesfully cruised Tystie (flat hinged main, cambered panel mizzen) from NZ to New Caledonia; and now having cruised Taiko (baggy panels) from Mexico to Nuku Hiva and not having enjoyed the rig one little bit, to the extent of talking of scrapping it (new sails, old yards and battens) and asking me what I would make to replace it, to get away from the problems that he's had. And my answer is lower angled yards, hinges, a little bit of barrel camber forward of the hinges, flat sail aft of the hinges.

By all means check with him first David but it would be great if we could all read the specific issues Martin had with the Arne type sails on Taiko during their Pacific crossing.

This debate remains fascinating: It will be enlightening to see how SV Rosie G gets on at scale (26ft!), although I suspect the variation in the high tech solid carbon battens will perhaps give some "hinge" effect. Having had experience of Barry Spanier's windsurf sail-making genius I cannot imagine it will be anything but superb, but I know next-to-nothing compared to the expertise on this forum:

https://reddogyachts.com/red-dog-yachts-blog/f/how-big-is-this-sail