Wow Mauro,

that was indeed quick testing and reporting! I like that spirit.

My thoughts were also, that such a 5 part pulley would be terribly hard to hoist...

Good idea, anyways! More learned on the way.

Cheers,

Paul

Anonymous wrote:

Today Toni and me are just lazy, mooring at a beautiful rock in the swedish wilderness, so I got plenty of time for some brain-itching thoughts. One of those goes like this:

______________________________________

Recently I was reading through some older threads in this forum, especially this one about Aerofoil shapes and entry angles. Reading through this, I stumbled upon Martin B. interesting blog. He wrote three technical articles about jiblet design for the SJR (here, here and here).

Somewhere within those lines it was described, that a slack luff decreases the camber from its designed value. Also the other way around: a fastened, straight luff increases the camber to its designed value. If I uncomfortably stretch my brain coils, and try to comprehend how a 2D canvas takes a 3D form using the barrel cut method, this even makes sense!

Now, if I look at this foto of one of Ilvy's panels, I can spot the obvious: the slack, round luff flattens the camber of the panel significantly - at least in the forward region, where its counts most, (and at least on this tack). This camber flattening is even further supported by the mast lift, cutting into the camber in the lower panels.

That's when I started thinking: A downhaul would tighten the luff, thus increase camber. If we introduce an uphaul (attached at the same position of the batten as a downhaul), which slackens the luff, would this decrease camber?

Could this be a way to trim the camber of the panels while sailing, by just adding uphauls and downhauls? Would be one less argument against the junk rig!

Cheers,

Paul

_________________________________________________________

(Yes, I know, this is against the 80/20 rule. Junks sail just fine without these further complications. However, there are also simple bermudan rigs and then there are those complicated, highly trimmable ones onboard IMOCAs, VO60s, etc... Each can choose according to their needs. And wouldn't it be great, if some day we would be able to advertise the junk rig without mentioning the restriction that it is a cruising rig, not a racing rig? Might be utopian... )

Hi Paul,

 I have an unsplit cambered sail with low balance (70% yard angle) on my kingfisher 20+. 
the looks beautiful with her yard pointing fiercely high to the sky and works well too.
Anyway as I set for the first the rig, the downhaul was too far  afterwards and the effect was a strong bend of the boom. Since I moved it forwards the things go better and the luff is taught without any noticeable boom bending. My little boat is quite stiff but I didn’t noticed any significant bending of the battens even when it blows a bit and the entire sail is up…actually in these conditions the only thing that bends is the mast…
As I reef, the luff gets slack and the sail looks not setting well.  
I don’t like this and was thinking to set a 5 part block on the forward end of the boom, a bloc on the forward ends of battens 3 to 6 and organize a pulley starting from batten 2 (counting the battens from the  top to the bottom). The line (4mm dyneema) would run from the 5 part block along the boom back to the mast and than down to the deck and back to the cockpit…

I don’t know if this makes any  sense at all….

Congratulations for boat, sail, ideas and voyage!!!

Mauro

Today Toni and me are just lazy, mooring at a beautiful rock in the swedish wilderness, so I got plenty of time for some brain-itching thoughts. One of those goes like this:

______________________________________

Recently I was reading through some older threads in this forum, especially this one about Aerofoil shapes and entry angles. Reading through this, I stumbled upon Martin B. interesting blog. He wrote three technical articles about jiblet design for the SJR (here, here and here).

Somewhere within those lines it was described, that a slack luff decreases the camber from its designed value. Also the other way around: a fastened, straight luff increases the camber to its designed value. If I uncomfortably stretch my brain coils, and try to comprehend how a 2D canvas takes a 3D form using the barrel cut method, this even makes sense!

Now, if I look at this foto of one of Ilvy's panels, I can spot the obvious: the slack, round luff flattens the camber of the panel significantly - at least in the forward region, where its counts most, (and at least on this tack). This camber flattening is even further supported by the mast lift, cutting into the camber in the lower panels.

That's when I started thinking: A downhaul would tighten the luff, thus increase camber. If we introduce an uphaul (attached at the same position of the batten as a downhaul), which slackens the luff, would this decrease camber?

Could this be a way to trim the camber of the panels while sailing, by just adding uphauls and downhauls? Would be one less argument against the junk rig!

Cheers,

Paul

_________________________________________________________

(Yes, I know, this is against the 80/20 rule. Junks sail just fine without these further complications. However, there are also simple bermudan rigs and then there are those complicated, highly trimmable ones onboard IMOCAs, VO60s, etc... Each can choose according to their needs. And wouldn't it be great, if some day we would be able to advertise the junk rig without mentioning the restriction that it is a cruising rig, not a racing rig? Might be utopian... )

Oh Paul,

You are pressing me to admit how lazy and cheap I really am. I like the KISS system as it suits my lazy nature, and I avoid all stresses of any kind. So here is how I made my junk rigs extremely cheaply.

I went directly, in person, to the main wholesale supplier who supplied all the local sailmakers, and initially I talked them into giving me a trade account (huge reduction) as I was technical secretary of the JRA at that time, but in the end I only bought thread, basting tape and sail numbers that way.

When it came to sail material I discovered that they had lots of what they called ‘ends of rolls’ which were too short for them to supply their big customers. The rolls were marked with cloth weight and length remaining in the roll so I simply took my time and selected a few rolls of the weight I wanted and more than enough to build whatever I was working at. The rolls might not have been identical weaves, but they were good enough for me to experiment with and were all quality material. The big point was that they cost even less than trade price.

I used 5 or 6 oz for Poppy as I had no idea what I really needed, I handling it I reckoned it would do, but with experience of how light the pressures on the cloth was in practice I then used lighter materials. For the Amiina Mk2 rig I got what was marked as heavy weight spinnaker cloth which felt like Terylene and marked at 2.5 oz and was priced in pennies rather than pounds so I bought what they had. Yes, I bought different material for the top panel. It was the same weight, felt the same but was in red to try to make the rig stand out, but here my laziness got the better of me and I just made the split top panel with the white cloth. By the way I don’t recommend making a tapered top panel split because it is a great fiddle and I doubt if it makes any difference to the overall performance.

I have photos of Edward thrashing about in ridiculous extreme weather for such a small boat with only 3 panels up and there was no mention of the material not being strong enough.

The leech lines on both Poppy and Ammina Mk2 were simply 3mm pre-stretch polyester, but you’re right, the luff lines were stronger. On Poppy they were 5 or 6 mm, and a right pain as the knots at each batten were big and lumpy, and got in the way, so for Amiina I did buy 3 or 4mm Dyneema and sewed the tails of the knots into the sail luff.

In practice there isn’t really any ‘downhaul load’ pulling the battens apart as each batten has its own DBP holding it to the mast and no slack to let it rise up the mast. The rig just hangs from the halyard.

I hope this helps,

Cheers, Slieve.

Hi Slieve, Graeme,

I do not want to advocate against downhauls, not at all. I want to adress the challenge of using downhauls with an unsplit, cambered junk rig with high mast balance, and how to solve it.

I have no practical experience with the SJR, only read about it and I readily admit, that I derived my description of strong downhaul forces on the battens by the DBPs from my own experiences of my boom downhaul on Ilvy (cambered, unsplit junk, high mast balance). Thanks for pointing me to the right direction: how you describe it, the downward forces of the DBPs are very low. Thanks a lot for clearing up!

However, you both describe the reinforcement of the luffs by adding a small line (4 mm or dyneema), which, in my opinion, should be strong enough to take more load than one could possibly tighten any line manually without using a winch. Thus, I would regard these luffs as being substantially reinforced. Enough to carry any manual downhaul forces, either high or low (regarding junks! I am not talking of those high forces of a bermudan rig). As I described in my post below, even the canvas of a flat cut junk should be able to carry downhaul loads to the next batten above - however, in a unsplit, cambered junk with high mast balance, there just isn't anything but thin air in between the battens to carry on that downhaul load from batten to batten. Only the bending resistance of the battens work against the downhaul forces, which is applied at about 1/3 of chord length, and thus is weak.

Cheers,

Paul

PS: I am strongly driven to try, build and experience my own SJR for Ilvy this winter with Slieve's design. Hopefully I can arrange my priorities accordingly! Slieve, did you also only use that 70g Spinnaker for the upper panels? If so, that's truely exciting!