Whoa! Before going any further let’s start being a bit careful with the use of the word "balance".

The last three posts, taken together, are going to be confusing. Stop right there. There too many different meanings given to “balance” – a weakness of the English language perhaps.

Bert Many thanks for chiming in. It was very good of you to bring your experience to the attention of all of us, so we could all learn from it. I would be glad to know that everything is OK now on your beautiful little keel boat.

Now,

• (1)   lets leave out of the discussion any notion about “helm balance” – ie lee helm or weather helm. Its not part of this discussion anyway – I just want to get that out of the way first.
• (2)   Next, lets get rid of Bert’s reference to “balance between jiblets and main”. There is no such thing, and even thinking about it makes me nervous. Forget it. That’s where the troubles started.
• (3)   Next, the all-important proportioning of a lug sail: the proportion of the sail outline which is in front of the mast centre-line. Actually, it is near enough, accurate enough, and much, much easier, if we forget about the sail altogether here, and just consider the proportion of a lower batten which is in front of the mast centre line. Exactly as Arne has done it if you look closely at his recent diagram.

I have heard this referred to as “sail balance”, “aerodynamic balance” – and in his recent post, Arne has referred to it as “mast balance”. I guess any of these terms would do.

• (4)   Now Arne has created a new use of the term “balance” by referring to the distance from the CE to the mast – and then in the next sentence talking again about “balance” and now it is unclear which “balance” he means. Arne, please belay that use of the word “balance” and find another word for it. Actually, because these posts are permanently circulating on the web, I am wondering if you would mind editing that recent post in some way….eg …
• “There is even one more balance factor to consider here, the distance from the CE to the mast.

• The sail with the shortest “CE to mast” distance will be the easiest to sheet in.
• In addition, a shorter CE to mast distance will ensure easier steering on a dead run. The Amiina-style sail is probably the closest we get to a square-sail for running before.”

I presume this is what you mean Arne. (Forgive me if this sounds a  bit “bossy” but I really sincerely to want to make sure this thread doesn’t result in the water becoming even more muddy).

OK, back to Arne’s creation.

For anyone who wants to keep on the conservative side regarding mast balance [actually, in his most recent diagram, Arne has matched the 33% mast balance of Amiina2] it looks to me as though Arne has once again come up with an alternative development pathway which is worth trialling. That low halyard angle, and that very low angle of the line from mast crane to CoE kind of suggests to me that the sail ought to drape nicely enough and require only the spanned parrel-downhauls to hold it to the mast. Provided the mast is kept vertical. (If other running parrels are required, I personally would reject it, because I think running downhauls are needed on SJR panels, regardless). I am not sure though, and would be keen to hear the opinions of anyone else who is familiar with the McGalliard running parrel downhaul system which I think is properly an integral part of the SJR. (Also, I believe I know of at least two SJR variants which are probably unable to use the spanned parrel downhaul system and it would be very interesting to know how they operate. I might be proved wrong here.)

Also, the jib proportions don‘t look too bad to me, now, comparing them with Poppy. You’ve got your six speed gearbox, smaller panels, finer reefing steps, and an extra bit of sail area up there where it will do the most good. Its wonderful to see that on the shorter mast – is there enough halyard span there to allow the sail to freely rotate? I think I’d give it a few more inches – but anyway, it beats the Amiina2 sail on that score. A bit more area for a bit less mast. Well done.

I have my doubts if it is a better performing sail than Amiina 2 – aerodynamically a step backwards in my opinion – but I can not see any reason why it would not work quite well enough that we may never really know. Now I suppose someone needs to try it. Will it prove to be the best of both worlds - or the worst of both worlds? It ought to be tried on something small, but size matters, and this sail might be at a disadvantage at small scale. There is no doubt whatsoever that for a smaller sail, less panels will be more efficient. However, a small-scale trial of this 7-panel sail would still prove whether or not it is a practical proposition.

Marcus, if you want to be the guinea pig, why not do what I did: knock up a quick small version of it in light weight material, and try it out for a season on a trailer boat. It’s a good way to get confidence with the sewing machine too, won’t take long – and for the learning you will get, may well save you time and money in the long run, especially if you will make the sail for your larger boat. I think that is what David has already advised, too.

My opinion? I still think it’s a step sideways rather than a step forwards. It may widen the range of possibilities for the SJR, which is a good thing. However I still hold to the idea that SJR is not worth it unless you get the best value from it - and to get the best value from SJR means putting as much emphasis as possible on those jibs, which is where the real work is done when going to windward. This means not going back to a lower mast balance, and not diminishing the size of the jibs. So I will be sticking to Amiina 2, still the simplest too.

Well, there you go –maybe it once more comes back to “horses for courses”.

PS Arne - I'm chewing on it. Funny you should use that expression - right now I am suffering from toothache and don't feel like going outside, which is why I am malingering at the keyboard instead of working on my project.

By the way, what is the meaning of "swinging the casseroles" ? It sounds intriguing, I have no idea of the meaning. I don't think we have that expression in English.

Anonymous wrote:

Balance, and then some more balance

When I drew up that first HM-style SJR master sail, it was based on Poppy’s sail. This sail has 10° boom rise and only 30% mast balance.

Now I tried to do the same based on the Amiina-style sail SJR. This sail has 5° boom rise and 33.4% mast balance.

The result can be seen below.
As can be seen, the halyard almost goes vertical and the line from the mast crane to CE only angles 10° out from the mast (vertical).

There is even one more balance factor shown here  -  the distance from the CE to the mast. This tells us two things:

• 1.      The high-balance sail will be easier to sheet than the low-balance sail (split or un-split).
• 2.      In addition, a hi-balance sail will ensure easier steering on a dead run. The Amiina-style sail is probably the closest we get to a square-sail for running before.

Now, chew on that!
Arne

(..time for swinging the casseroles here...)

This is really interesting to follow!

A few questions from my kitchen sofa,

- Would the balance of the HM/SJR be enough to not need the parrels (other from the one Slieve uses) for keeping the sail in place, how is the “draping” (as Graeme mentions)?

- The proportions of the jiblets of the HM/SJR differ quite a bit from the Amiina, what would this mean in regards to performance/functionality? I think Slieve had a thought about those (the proportions), one of the reasons for not adding more panels to the sail. 

If these points check out fine, I would really consider the HM/SJR for my own project, maybe guinea pig it ;). It looks like the mast position would be the same on both of these types, but the HM/SJR can pack a bit more sail on the same mast length.

/Marcus

I quite agree Arne, and I had hinted at that when I wrote "A true force diagram would look at the centre of gravity of the sail bundle, actually, not the yard slingpoint".

I didn't realise how much further ahead than me you were in your thinking. (Silly me).

I think the halyard angle with respect to yard slingpoint (as opposed to a line from the halyard crane at the masthead, through the centre of gravity) is probably still worth adopting as a design parameter, because neither actually paints the true full picture, but the former is simpler and pretty much nails the issue, its simple to calculate and display, and its something you can "get your hands on" so to speak.

For this reason I still think your expression "Keep the halyard angle  low" is a powerful and useful motto, which unifies so much of the theory about yard angle, balance, mast height etc etc" and I thought it was a very good summary which goes near enough to the heart of the matter.

Provided we agree on a definition (otherwise just more talk and confusion). 

I take it you agree that halyard angle is the angle between the yard and the vertical?

Edit: Why not have both in the tool box? I looked again at your drawings and using the C of E of the sail as an approximation of the CoG - which you would display anway - its easy enough to draw a line from the masthead and add in that "gravitational offset angle" or whatever you want to call it - and that angle does help to understand something about the way the sail would drape. 

Halyard angle has a lot to do with the ease or difficulty of hauling up that last panel. Your suggested "offset angle" is probably closer to the question of drape, and parrels etc. although both play a part.

The actual force diagram is a bit more complex than first meets the eye, but I am too lazy to go any deeper into it, no need, I think.

Good one, Arne.

Amiina’s sail certainly was the most balanced of them all

I guess that's because it is because of its perimeter shape and because it has the highest balance in the other respect (33% sail balance) which in turn is allowed by the split in the sail, and which also dicates a lower yard angle - it goes on and on. Once one parameter changes there is a cascading effect, and other things have to change too, or the concept behaves unpredictably. Which is why it is best to leave these things to people like you, who have design experience, and not tinker with a known good design (which, after-all, is just a collection of well-harmonised parameters).

Which brings me to an earlier question - you haven't yet explained what kind of system you would design for holding a HM/Poppy hybrid to the mast, while at the same time keeping the luffs straight in every configuration of reef. Neither has David. I suspect there is no simple way - especially in David's short raked mast Poppy/Siblim variant. I'd love to be proved wrong, because I love the handsome look of David's concept drawing, and I like that your idea crams on a little more sail area. But would they work in practice? The more I think about it, the more I marvel at the exquisite simplicity of Amiina Mk2.

To be precise...

Yes. Keep the halyard angle low.

That's a perfect summary Arne, which unifies many different approaches to what is essentially the same goal.

Let us now define precisely what we mean by "halyard angle" as there is still room for ambiguity.

Please note that the Kelt 8.5 in Arne's drawing has been given a vertical mast and therefore represents a special case, not a general one.

The purpose of the halyard is to overcome gravity (a vertical force) so that the sail can be made to rise up. Because the lug rig lifts from a slingpoint on the yard which is not directly below the halyard crane, the halyard (the force vector) is necessarily at an angle from the vertical, and it is the horizontal component of this force vector which we must fight against with various types of parrel - and which it is desirable to minimise.

Minimise the halyard angle - and you have minimised that pesky horizontal component.

(A true force diagram would look at the centre of gravity of the sail bundle, actually, not the yard slingpoint. But the yard slingpoint diagram is near enough for discussion purposes. Furthermore, sheeting forces come into play once the vessel is under way, and a whole series of dynamics come into the picture, so the above simple diagram is far from a complete picture of reality. However, nothing is served by bringing in further complications. There is a simple principle which needs to be understood here, and the above diagram is near enough for that.)

To get to the point: the halyard angle should be defined as:

"the angle between the halyard and the vertical"

and I would like to see that, together with a sketch, added to the junk rig vocabulary.

Now the same principle applies to a forward raking mast arrangement, but the forward rake changes one's perception of things, though it does not actually change the force vector diagram one liittle bit, and this potentially confuses things if we are not careful. People may wish to measure their halyard angle - perhaps compare notes. To compare apples with apples, the term "halyard angle" must mean the same thing to everyone, regardless of mast rake. Also, gravity remains vertical even if the mast is raked, and it is on this that we must focus. Halyard angle is not the angle between the halyard and the mast, it is the angle between the halyard and vertical.

It just so happens that on Arne's Kelt 8..5 drawing - and on Slieve's SJR designs the masts are vertical and this small but important point risks being overlooked.

Precision of meaning can be important. Here is an example: The definition of "balance" is a little vague and since Slieve and others first introduced split rigs and aerojunks etc, it has become open to misunderstanding. Lack of precise understanding of what Slieve meant by "balance" led to at least one documented example of a split junk rig being built which was over-balanced.  (with consequences).

Halyard angle is associated with mast height, among other things, and I can envisage a similar mistake being made if that parameter too is ambiguous. In fact I think I know of one. Can we agree on the above definition? I think it also strikes at the engineering heart of the matter, which is: what is left over when you cancel out the gravitational force. We all understand that in our Newtonian world, gravity acts vertically.

Now, if any one is further interested - how many ways can you think of, to achieve minimum halyard angle? There are many.

Thank you very much everyone involved in this discussion, I learned a lot.

I think this final conclusion from Arne is a very important one.

Rudolf