The meaning of art is in the eye of the beholder.
OK OK I’m a terrible tease. I made a bunch of sail sketches recently, just to see what kinds of sailplans I could squeeze on to Tammy. You can take a look here https://www.flickr.com/photos/rptb1/albums/72157686474634343
This is just the result of me enjoying fiddling with the prettiest one.
It has 4.5m battens in the main section — about the longest I can get away with — and 1m panels because sailcloth I’ve seen comes in 114cm widths. The yard is at 40° rather than 60° on the original rig, as suggested by David Tyler to bring the rig and CE forward. But that also allows me to shorten the top two battens and keep the total height of the rig the same as the original, to reduce weight aloft. That naturally produced a curved shape, which is just aesthetically pleasing and may not be practical.
The rig is about 20-25% forward of the mast, which is quite a lot, but not too much as far as I can tell so far. Split rigs have up to 33% ahead, and I could split some of the panels.
The main panels are parallel, so this is really just an H-R sail in disguise. That allows me to use, for example, Roger Taylor’s HHH system for camber, or my tied alternative, and have replaceable panels (some split, some not).
But mostly, I just like the look of it!
Actually I mean “shorten the yard and top batten”.
Also, the curved shape is a tribute to Jester.
Makes sense to me!
Nice work Richard! You are way ahead.
Here are a few additional queries:
Sheet to the upper batten?
Double check Van Loan?
To split or not to split?
But certainly no aero / wishbones?
Angle of lower batten bit > 110 degrees?
How about sailcloth from upper batten to mast tip instead of yard?
Please elaborate some more.
Even art deserves elaboration!
I should probably experiment with a long upper batten and sheet. With the smaller upper panels it may not make much of a difference.
Thanks for reminding me about Van Loan. I will look for people who advocate his sailplan, and also read about the Reddish rig with a short yard.
I’m definitely going to try out splitting. The compromise is this: once you split you can’t move the whole sail fore and aft. The luff of the main panel needs to be tight against the mast (or so I understand). With a low AR sail like this, fore-and-aft adjustment might be very important. You might be wondering why I have such low AR. Well, I really want the area for light winds, which are Tammy’s main weakness at the moment.
I think the aero junk is really good thinking, and I’m looking forward to reading Paul’s new article about it and studying Pete Hill’s design too. Right now I think it’s a big jump from where I am and what I have learned, so I want to play with conventional battens first.
I’m not sure what you mean about the lower batten. The angle in the picture allows me to get sail area forward while still being able to tack standing up — something I find very valuable.
The sailcloth yard triangle idea might not work so well with this plan, where the yard is already very high. The shorter yard might not need so much strength. There’s an interesting discussion about yard forces and breakage going on at the JRA forums: http://junkrigassociation.org/technical_forum/5276531
Thanks for the questions — they’re very useful for getting me to write down my thoughts, no matter how good or bad!
For an off the wall idea could you have 2 up haul lines either side if the mast through turning blocks at the top attached to the bottom 4 battens i.e one line for each batten, the bottom batten being the boom. These lines could be tensioned in turn to induce camber in the bottom 4 panels. Think of it as a Cunningham in reverse. This way you could keep the existing rig and sail etc. If this would work you could adjust each line to give differing levels of camber in each panel and also reduce the camber as the wind strength increased by letting the lines down. This would possibly give you a mini reefing system prior to dropping panels.
Most junk rigs already have lines a bit like that — the topping lifts and mast lift. It’s already very easy to induce vertical camber in the sail, but in my experience this is bad news and reduces performance upwind. In fact, I sometimes re-tie my boom downhaul to a batten when reefed to get the sail tight.
The desirable camber is horizontal, to get a more wing-like shape and extra sail lift. In other words, like the belly in a Bermudan main. I summarized the techniques for getting that shape in https://tammynorie.wordpress.com/2014/08/15/new-sails-for-tammy-norie-background/ but to that list we must now add wishbone battens and the aero junk rig.
Upward reefing does exist on some Chinese rigs and it’s mentioned in Practical Junk Rig. If I build this very large sail it might make some sense for me too. I think of this as my studding sail system!
I hope I’ve understood you correctly.
I was thinking that by lifting the battens and boom they would be encouraged to induce horizontal camber in the panels in that the sail would no longer hang or be pulled flat. If the existing sail is tensioned between its halyard and some kind of down haul with the down haul loosened and these additional lines tensioned they would create a “bagging” effect in the sail. The re tensioned down haul would pull against the “reverse Cunningham lines instead of the main halyard. I’m not sure what would happen at the main sheet end of the boom/battens though.
I may be missing something, but I’ve never noticed any horizontal camber being induced by vertical slack. Bear in mind that the sail is suspended between very stiff near-horizontal battens. You get “scalloping” (i.e. vertical camber) but nothing in the other direction. I tried inducing more slope in my battens to see if I could get some horizontal camber, but it was negligible.
There are stories of the Chinese pre-stretching their panels to make them baggy to get horizontal camber. Tammy Norie’s original sail is made of terylene (Dacron) sailcloth and so hasn’t stretched.
There are some claims that highly fanned sails (with battens at widely varying angles) develop some wing-section horizontal camber. I built a model sail with highly fanned battens to see if I could induce this, and I don’t really believe it.
I may still not be seeing what you’re imagining. Perhaps we need to get together with a pencil and paper 🙂
It is likely a mix up in the use of horizontal and vertical in this context. I suppose my idea is like creating an adjustable version of the Chinese pre-stretch approach. Much like creating a vertical concertina effect. Producing camber like a Bermudan main, i.e wing like along its horizontal width with the fixed stiff battens is obviously a challenge. Could each panel be separate and in essence loose footed on the battens so the battens could act like a Bermudan boom with an outhaul adjustment/attachment point at the batten ends? Incidentally I did consider converting MAI to a junk rig at the start of the re-build as there was no rig with the boat. The simplicity of the junk rig really appealed to me but I elected to stay with the Bermudan rig as I always seem to be sailing to windward in my sailing area.
Yes, you can treat each panel like an individual sail. I talk about this a bit in my post about the tied hybrid idea https://tammynorie.wordpress.com/2015/06/22/presenting-the-tied-hybrid-system/
One of the problems of a simple loose-foot approach is how to get the belly of the camber forward to get a good wing section. If you just make the panel loose it will tend to form a belly in the middle, losing lift, creating drag, and shifting the CE back inducing weather helm.
On a Bermudan main you can shift the belly forward using the mainsheet and kicker to tension the leech. That’s a basic trimming method I’m sure you’re aware of. The junk rig is low tension and we don’t use long axes of tension to change sail shape. It’s be very hard to do that and retain all the advantages of the rig.
So camber systems for junk rigs tend to focus on how to pre-shape the panels or battens to get the camber in the right place. Hinged battens and barrel-cut panels are the most common methods. I like Roger Taylor’s HHH system for simplicity and flexibility. My tied hybrid is merely a thought experiment.
Aero junks use a flat sail that leans against the inside of wishbone battens to get a wing shape.
We do go upwind you know! In a river I often beat Bermudan boats upwind because of my superior tacking ability. But a Bermudan will have a better VMG upwind in open water.
You’d be very welcome to come for a sail with me and try it out.
You raise some very good points. How about a Bermudan style batten pocket in the middle of each panel. You could then add a fibre glass long batten, thicker at the mast end and tapering towards the leach into each panel. Thanks for the offer of a sail.
Ahahaha I love the idea of adding *more* battens! I’ll have a think about that one.
If you look closely at the video of pictures of Amiina from the August bank holiday (earlier in the blog) you can see little battens in the centre of the jiblets. That may be a related idea. I’ll have to ask Edward Hooper.
I think it looks very pretty, but am not sufficient of a technical junkie to comment on its possible merits. I leave that to others in the JRA
I think you have a good grip on the most important aspect there.
In fact, there probably isn’t much to say about this sail shape. It’s quite conservative. It’s not much more than a fattened-up version of my H-M sail. The real difference will come in the flexible rigging.
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