This thread has grown quite rapidly which suggests that it might be useful to give some background information. I can see where some are coming from, but would like to add a note of caution to some of the ideas which have appeared here.

The original Poppy rig, and the quite swift drift towards the Amiina Mk2 rig were no accident. They are out in the public domain and if anyone wants to modify them that is their own free choice, but the resultant rig will ideally have its own name/ label to identify it from the rest. The reason I suggest this is that experience has shown that those who have faithfully copied the original ideas have achieved results similar to the originals, and a number of those who have deviated any distance have later approached my off line to try and find out why the results have been poor.

A lot of thought went into the problem of improving the windward performance of the humble junk rig, even though the basic principle of obtaining a good Lift/ Drag (L/D) was fully understood. Lift was easy, but total drag is made up of a number of different elements, induced drag, form drag, skin friction and others, and the reduction of these may well be more important than the increasing of the lift. Poppy's rig was a 'proof of concept' effort, with no guiding light, and a big leap of faith. As it was being built many little problems had to be solved, and a lot was learned.

One aim was to use conventional sail-making techniques so that the design could be built by commercial sailmakers, hence the use of round and broadseam for the main panels, but it was clear that to get the envisaged camber shape into the jibs would require a seam running into the top and bottom front corners with well tailored taper included. The flat shelf foot was considered, and eventually developed into the new idea of the angled shelf foot to try to control the shape of the leech area at the same time. Even with this original idea I feel there is still work to be done to find the best camber shape. The 45º shelf made sense as the square root of 2 is instantly recalled.

As the rig was being built the problem of shaping the panels became clear. The shape of the clothes for a jib with different chords at head and foot, and with battens that are not parallel were calculated on a spreadsheet, but still required 'adjustment' as they were sew up. They are not an ideal challenge for a first time sail-maker. Working on my own I found it an interesting exercise, and the Poppy rig has may experiments sewn it, as part of my education.

I was confident that the rig would perform well, but even so, was surprised at some of its strengths. It took some time before I could understand where all the performance came from. When the first sailor with junk rig experience sailed it he went away with a silly grin on his face muttering, 'I must have it', and a week later phoned me to say that he had just bought a sewing machine, and could he have the design for his boat next week, at the latest! There was no way I could have talked him through the building of the Poppy rig over the phone, so I had to over draw the profile to make it a practical proposition. We worked well together over the phone, and he built a successful sloop rig to replace his previous 2 mast set up. Since then all the rigs I have drawn have followed the 'more angular' shape for the same reason.

The Amiina Mk1 rig was my first attempt to provide the design for a commercial sail-maker to build. Unfortunately we did not get the sail area right as the racing brigade would not admit how the Splinter 21 rig had shrunk. It was not helped by the efficiency of the SJR so a smaller rig was required. Even so, when I asked Edward to check some measurements on the Mk1 rig I found that the sail-maker had not accurately followed my numbers and had variations between identical panels. The Mk2 rig was therefore going to be home built to avoid this problem. I also wanted to simplify the design as by that time I was getting quite a few questions off-line from those trying to build the Poppy style rig and getting stuck. On the other hand, Edward reasoned that if the split added performance then why not split all panels. He got his split, but I still do not recommend it as apart from the camber shaping problems it introduces a potential problem with luff and leech lengths in the top tapering panel, where if the jib is moved fore or aft it can result in slack luff or leeches. The Mk2 rig was an attempt to make a practical rig for the average experienced sailor to build, and still retain all the key features that I believe effect the performance. Those who have copied it seem fairly happy with it. KISS refers to building as well as sailing and low stress.

Prettiness, which is in the eye of the beholder, comes at a price. The selected yard angle, aspect ratio and balance all have a reason. They have already been proven in practice. The angular shape simplifies construction. The reduced number of panels is no accident. Experience with the rig suggests that there is good flexibility in wind range for each step in sail area. On Poppy I always reefed in 2 panel steps, so why not simplify the build?

I hope this is of some help.

Cheers, Slieve.

Anonymous wrote:

Hey Paul G. - I meant to add (I'll put it at the top) - your boat does look beautiful, you should feel proud - and I bet you are loving the sail too!

Marcus

The prize for “suggestion of the week” should be duly awarded to Len. I don’t agree with making do with a 9m above partners mast (unless you opt for a 2-masted rig) – I think you would regret it. However, Len’s brilliant afterthought suggestion of a tabernacle could well give you an extra 2m of mast height. If you look at Annie’s blog, you will see that she

I am not sure I think 9M is appropriate. My main point is that: as soon as you set one dimension in stone (11M spar), you have to follow the rest of the steps from there and decide if that makes sense. It appears that boom/batten length and ease of playing with them drive a higher AR as well as other factors. A low AR is a reefed high AR sail.

I also agree with more battens being better. I have always though _some_ of the SJR sails looked like they needed more battens but, as they seemed to work out just fine, thought it not worth mentioning.

My wife and I are hoping to look at a Columbia 36 when we get our car back. So I have been looking at what kind of rig I could put on it. I have come to the conclusion that a SJR sloop with a high enough mast would be easiest. My concern would be weight for raising the sail. With a schooner/ketch (yawl would be possible too I guess) the foremast would have to move forward with the most practical position being just behind the chain locker. The SJR may work there if the mizzen was big enough but a foresail with less balance would probably be better all around. Fully rigged (three sails) would allow the mast to remain where it is but would probably require the mizzen mast to be quite far back with the problems of dealing with sheets that entails. (aside from expense and complexity) For those interested, the under water center of area (sans rudder) is very close to the keel bulkhead just behind the mast step.

All that to say that this thread has been quite useful to me as well. While I really like the simplicity of the SJR, it is clear that drawing up all the options I can think of is in order. If the sails and rigging it has are usable, we will run with that for a bit, otherwise motor this summer I think. So I have some time to think about it.

For what it's worth, I've gone back to my SibLim 10m design, adjusted the LAP to 11.4m, and then put Poppy's 50.8sqm SJR on to it such that the foot of the sail is 1.14m above deck, so that a tabernacle can be used with ~10% mast bury. The angle between halyard and mast is then 21˚. Looks good to me.

Hey Paul G. - I meant to add (I'll put it at the top) - your boat does look beautiful, you should feel proud - and I bet you are loving the sail too!

Marcus

The prize for “suggestion of the week” should be duly awarded to Len. I don’t agree with making do with a 9m above partners mast (unless you opt for a 2-masted rig) – I think you would regret it. However, Len’s brilliant afterthought suggestion of a tabernacle could well give you an extra 2m of mast height. If you look at Annie’s blog, you will see that she installed a tabernacle, arranged so that the heel of the mast is at deck level. The lower tabernacle, which will extend down to the keel, can be regarded as a lower mast extension. It won’t help in any way with interior accommodation – but it does give you some extra mast height. The advantage Annie sought was not needing to have a hole in the deck to keep watertight, as the mast is entirely above deck. I would consider forgoing this advantage in order to sink the mast a little deeper, ie get a little extra “bury”, as I will explain in a minute – but if all the rest of the engineering is sound, it’s a matter you can decide for yourself. (I am planning a "sunk tabernacle" for my own project, to allow a tallish mast - and a "secret weapon" which has been brewing in my mind ever since I put a sunk tabernacle into my little trailer boat.) A tabernacle extending 1 m above deck looks a little prominent on paper, but when you look at the beautiful Fanshi, you can put any concerns about that aside.

Now, from an engineering point of view (and I am assuming the specs of your two tubes pass muster, you can check those details anyway) an 11 metre mast in a 1 metre tabernacle meets the “10% bury” rule – just – with nothing to spare. So that gets you to 11m “above partners” with the tack of the sail a little higher than 1m. That gives plenty of room for parrel-downhaul spans if you follow Slieve’s system – and it also allows plenty of height at the aft end for sheeting. The only problem is, its still not enough height at the mast head to give you the full area of sail you should carry.

Why not (if the aluminium tube specs allow it) add an extra 3 m to the top of the mast, in the form of a wood, aluminium tube or carbon fibre, or glass fibre extension? Give the mast an extra 0.5m bury into the tabernacle (in which case you lose the advantage of a 100% sealed deck) and put on a decent sail, along the lines suggested by Slieve – or any other you like – and aim to match at least the working sail area you had before. This would give you a 1.5m bury and a 13.5m LAP (length above partners) mast.

Edit: You could optimise those numbers a smidgeon and reduce the length of topmast extension by a few cm if you want to go to exactly 10% bury - and as David has pointed out while I was writing this - you can squeeze another 0.4m from your two 6m tubes as well - this further reduces the length of the suggested topmast extension, down to 2.5m perhaps, or thereabouts.

Or, if you want to stay 100% above deck, scale down the top mast extension, raise the tabernacle slightly, and see how much you can get, allowing 10% bury – I think you might still squeeze in with 13m LAP and a 1.3m above deck tabernacle – and a slightly reduced potential sail area. Again, slightly better than that actually, following David's suggestion. You might need something like that anyway, to clear the deckhouse, depending on how much rise of batten you eventually decide on and where the sheeting goes - without a drawing its a bit hard to say, but you can look into that anyway.

I think Len’s suggestion plus a short topmast extension opens the possibility of a fairly decent a sloop rig, if that is what you would prefer. Do not skimp on mast height (as I think you have done in your most recent drawing). You need as much halyard drift as you can get, for a number of reasons, and if you try to cram too much sail onto a mast which is a smidgeon too short, you will regret it.

Summary: If you want a sloop rig, your first concern must be to get the tallest mast you can.

After that, you can look at the various forms of junk rig and see what gives you the best out of the mast that you have. The choice of which type of junk rig will also have some effect on where the mast (tabernacle base) is placed, don’t forget – but otherwise I think the choice of sail type is of less importance than first organising a high enough point for the halyard, and getting on as much sail area as you can, since you are struggling to match what your current rig gives you.

In the bigger scheme of things, you need sail area, camber and a means of managing it. The rest is detail. All the modern junk rig types have their advantages and disadvantages, they are all good.

(When choosing the sail type – as you have realised - with a higher yard angle you can get a little bit more sail area onto your chosen mast. This might influence you a little towards Arne’s Johanna rig. The difference is not that great that it’s a game changer, but it’s definitely a thought. First and foremost – decide if you want a sloop or not, and if you want a sloop – you’ve got to get that masthead up to 13m+ in my opinion, so start from there).

Step 1: run your proposed aluminium mast tubes past the people who have expertise in this area. They will want to know outside diameters, wall thickness and grade of aluminium. In addition, I would suggest length  of proposed topmast extension (if you are going for a sloop) - and some idea whether you are thinking of inshore cruising or whether you plan a trip around Cape Horn.

Step 2: decide where you want the mast to be placed and accordingly what type of junk sail will fit best -  and then you can start worrying about scaling up batten lengths and all those other secondary details.

Anonymous wrote:

Thanks for the numbers Marcus. It all makes sense.

High-cut and staysail at 33 sq.m, and almost the same as the Genoa is a fairly typical rig. A SJR of 54-55 sq.m set with the 50% overall chord (Jib luff to Main leech) at the same longitudinal position as the centre of area of the original rig should be fine. Scaling the Amiina Mk2 rig by 1.82 would appear to give 54.5sq.m, and a jib luff to main leech of 5911mm, and 5933mm along the batten at 5º rise. Then if you place the mast at 33.3% overall chord you will have the mast position.

How does that look?

Cheers, Slieve.

I don’t really know which figures to scale (other than the battens). What are the original measuring of the Amiina MK2?

/Marcus