“I'm reading this in the "scary" sense, as it's precisely what I experienced in Amiina. A light, over canvassed boat is at risk of being blown down, filling and sinking, though I guess Bert's boat should be safe enough.”

David, you really do yourself no credit in writing such emotional nonsense. It must be clear to everyone by now that you are determined to rubbish the split rig, from even before you had your single experience of it.

We sailed the rig that you had your one experience on in a boisterous Round the Island Race and achieved a creditable result despite not sailing it well, and at no stage was there any feeling of insecurity. We would have been fools to have done so if we had felt “at risk of being blown down, filling and sinking”.

“All I am saying is that is unsafe to go for the absolute maximum balance, with the risk of overbalance. That's all there is to discuss here - what figure to put on the amount of balance.“

It is not unsafe to use a balance that has been systematically tested and proven to be safe and without risk of overbalance. It is butterfly engineering for you to pluck a figure out of the air and suggest using it as a maximum when tested results are available. That is the amateur approach to an engineering problem which if generally used would still have us struggling to achieve powered flight. If you think Edward is being defensive he is only reacting to your continual uninformed criticism which I also find extremely tiresome.

It is clear that Bert's rig has not been built to the information I tried to make available, and the question has got to be what has gone wrong. It could be my writing and/or Bert's translation/interpretation, but certainly his resultant understanding and build is not what was intended. Unfortunately I have not had a chance to chat to him, but from the two photos that I have seen there clearly are problems. The first photo showed that the initial balance was not as intended, and the later one seems to suggest that the camber is also not as intended. We need more photos, and maybe even the drawing of the panel patterns to make a more informed assessment, but it appears that the jibs have a hooked or tight leech which is back-winding the main panels badly. Tight jib leeches will also have an effect on the rig's ability to freely feather into the wind, and will effect the overall stability. I suspect a fully flat sail would balance at around 25%, similar to a true symmetrical hard foil. We need to follow a systematic analysis of the problem and not make butterfly adjustments.

The comments in one paragraph about the rig feathering and in the next saying it won't feather is confusion, and broaching through 180° is also not very clear. What is the total sail area, and what is the the oiginal designed junk rig area? Was the designed rig a flat Hasler/ McLeod rig? Is the boat being overpowered with a potentially more powerful rig? There is at lest one case of a boat becoming unmanageable when simple camber was introduced, and with hindsight was probably due to the professional sailmaker getting the shape of the camber wrong.

Another question could be, is your mast vertical or leaning back a little with the boat in sailing trim and your weight in the cockpit? If the latter then gravity might tend to 'sheet' the sail in in light airs, which will fill the cambered sails and drive the boat. It is difficult to make an informed assessment until we know more about the build and set up, and pointless to simply speculate.

Cheers,  Slieve.

Arne Kverneland wrote:...

It appears that the sail of his Runa, has a labile balance. I can only speculate why it is so, but here is my armchair idea:

Could it be that the jiblets are cut so they effectively are ‘sheeted in’ closer than the main panels? My thinking is that, as the alpha is reduced, the main panels are losing drive before the jiblets do. That could destabilise the rig. The obvious solution is that Bert makes a new set of jiblets, which he cuts to have a ‘slacker sheeting’ than the ones he has now. In my head, from a stability point of view, it is it better that the jiblets luff a second before the main section, than the other way around.

Does that makes sense?

Arne

Hi, I have uploaded a photo of my sailing in calm weather with the new jiblets cut to 29% balance with main including slot.

You can see that they have a broadseem in the middle  which is unconvenient, but as the old jiblets were cut down from 110cm to 80 cm at the leach the camber had to be adjusted by those broadseems.

The jiblets have a sheeting angle of 8° degrees.

The small red rectangle at the top of the picture indicates the winddirection, sail seems to be sheeted in a little bit  too much (but as I said: the sail searches this position by itself, sheets are totally eased, 1-2bft). The main shows a belly to weather which indicates that too.

Sail is not set as it should (gap should be nearer to the mast). The battens still have their old length, will be cut to save weight and to avoid hazzle of lines wooling round them.

Now to the fact of depowering the sail:

I will try to loosen the downhaul, and I will loosen the sailcatcher (lazy). Sail should move then more freely.

As my mistake shows, there is clearly a limitation of sailbalance, mine was 37%, which was without doubt too much.

Bert

robert self wrote:

I think one thing can be said for sure: a 33% balanced rig will, on average, have a (slightly) longer response time than a 10% balanced rig 'cause the sail's turning moment is a function of wind force and turning arm (equals distance betwn axis of rotation (the mast) and horizontal cntr of area of sail). Geometry dictates a 33% balanced rig has a smaller turning arm. Sometimes that's a positive and others a negative. One man's response time is just too slow for comfort, perhaps?

But the same can be said of a high-aspect-ratio sail versus a low-aspect-ratio sail. Everything else being equal, the turning arm of the high-aspect-ratio rig is less than the turning arm of the low-aspect-ratio rig.

All you can really do is pick your compromises and adapt.

robert self

I'm confused on your physics here.  A longer turning arm also means a much longer trek to get around the compass points.  What keeps a sail from instantaneously assuming the new position is inertia. And our rigs tend to have more mass further from the axis than a Bermudian, due to the squareness of it all.   In order to turn faster, what with the conservation of momentum thing, a smaller radius is usually best, no? 

Hello Bert,  

I've been following this thread with interest as I am still in the process of getting a split junk dinghy onto the water.  Other things keep getting in the way and I have a bermudan rigged dinghy to sail so less pressure to get it on the water.  

I too took the 33% balance as "Sail Area" and not total profile forward of the mast and will either have to build a new jib or cheat for the moment and shorten the leech by an appropriate amount increasing camber but decreasing actual sail area until I do build a new jib.  

Bert, I think that both Arne and Alain Herter may have both identified part of your problem.  I took another look at the photo of the rig in your album.  

I'm wondering what are the camber percentages for the jib and main?  In the photo they both look almost flat to me.  And what is your sheeting angle for the jib panel? and the panels do look to be very stretched and flat on the photo.  

In the photo, the jib sheeting angle looks to be non or almost non-existent.  This would have the same effect as a "backed" jib on a conventional Bermudan rig and be more inclined to pull the bow of the boat to lee.  On my bermudan dinghy, I measured the sheeting angle of the jib to the centreline as approx 23 degrees to leeward.  Forgot to measure the midsail jib camber unfortunately.  It wasn't very much though. 

So Arne may be right,  not enough sheeting angle may be pulling the jib to leeward and not allowing the whole sail to feather fully into the wind.  Or it may be that you still have too much camber too far forward on the battens as well, generating too much lift, though it doesn't look that way from the photo.  

Also in your photo, Alain Herter mentions that you may simply have too much tension on the downhauls and again, looking at the photo,  the panels do look very stretched which may make them less inclined to rotate around the mast. 

With that sort of tension, is it easy to push the sail around the mast with the tips of your fingers.  Easing the tensions of the batten parrels/downhauls could be part of the solution to the non-feathering of the sail.  

With regards to the "Scary" comment,  I'm with David on this one.  A boat whose sail won't feather is not confidence inspiring, though Edward and Slieve have since sorted out what seems to have been a teething problem on Edward's rig at that point in time.    

Hope you come up with a solution, Dave

Hi Edward

I don’t doubt for a second that your present rig behaves well, as you describe. On the other hand, Bert seems to be a resourceful chap who understands his boat quite well, so I don’t doubt on his report either.

It appears that the sail of his Runa, has a labile balance. I can only speculate why it is so, but here is my armchair idea:

Could it be that the jiblets are cut so they effectively are ‘sheeted in’ closer than the main panels? My thinking is that, as the alpha is reduced, the main panels are losing drive before the jiblets do. That could destabilise the rig. The obvious solution is that Bert makes a new set of jiblets, which he cuts to have a ‘slacker sheeting’ than the ones he has now. In my head, from a stability point of view, it is it better that the jiblets luff a second before the main section, than the other way around.

Does that makes sense?

Arne