Well, that looks like a delightful inshore cruising-camper with a very nicely proportioned rig. I will be interested to know what John Wellsford thinks, and Slieve. It looks really good to me.

Is that a shallow sail catcher you have rigged on the boom? I am not sure if it is, or if it is quite deep enough to fully muzzle the sail. If it is, then I think you could do away with that forward lazy jack which is interfering with the camber of the bottom jib panel.

(I found with my SJR that a sail catcher is worth having as lazyjacks don't muzzle the jibs properly, whereas a sail catcher does - and if you have a sail catcher then you don't need the lazy jacks - just lifts fore and aft, and the forward lifts can coincide with the slot.)

I thought your mast was going to be too short, but you seem to have got away with it.

Well done. Your boat looks a treat. 

It has been a while so I thought I would share an update on the SJR development for Cirrus.

To get myself into the method for making the sail I started of with building a few panels as a quarter scale model. This was a very useful exercise and helped my understand the material, required seam widths and how to get the sewing machine to do something like I wanted it to do. It also allowed me to do some "wind tunnel" tests in the alley down the side of my house with some interesting results. I had designed both the jiblets and the main panels with 10% camber. It was obvious from the model that air exiting the jiblets was flattening the leading edge of the main panels. So I went back to redo the design of the main panels and also discovered the thread on this site about catenary curves. I decided that a catenary curve was more representative of the shape that each panel would take. Using this approach a 10% camber turned out to be very similar to an 8% camber using the angeld shelf method. This turned out to be a long way round to get to the same conclusion others have reached that 10% camber on jiblets and 8% on the main panel is a good compromise.

This isn't a particularly big sail (15m2). I have used 3.8oz ripstop nylon which is very flexible and relatively easy to sew in a smallish space. My dinning room was kitted out as a sail loft with a few sheets of plywood. I created patterns for each panel on QCad and had these printed out full sized on A0 sheets (sometimes more than one and taped them togetehr) to be able to transfer the shapes to the material. I found that a fiber tipped water based pen was best for drawing around the patterns and markign out the various seam lines etc. Then there was a lot of sewing. It has taken me about 15 days to construct the sail. More than twice my initial estimate. The pressure was on to get it all finished and ready for the start of the season but Covid-19 did take the pressure off and making the sail provided a nice project to do indoors.

The sail is now on the boat, rigged and ready to take sailing once the lock-down is lifted. Note that in the photo the sail isn't fully raised or the sail bag dropped to its working position. It was a bit too windy.

I like your belayjng pins and partner arrangement.

Here's a sort of visual comparison between the 10% and 8% mains models. You can see the difference. (Jibs are 10% and 12 degrees.)

Also, here's Dave D's Wayfarer SJR sail, this looks to have a large camber in the mains, maybe equal to the jibs. It would be good to know how that particular detail worked out - Dave?  (Dave also has some good photos of making the sail in his public photo album.)

Robert, I'm looking forward to the write-up.

The thought and preparation you are putting into this project inspires me! I have created a “Cirrus” folder and look forward to more drawings and photos. Instead of paper models, I made a full size one out of plywood and used it as a “tailor’s dummy” when making the sail (did you see that here?) Slieve says that’s a waste of time, but does recommend the paper model.

I have a feeling you will have no problem making the sail, I found that part rather fun. I still say the challenge will be to get a set of running rigging which all fits, and works, and “folds up” easily between outings. The trailer sailer does seem to present its own special challenges in this regard, and I look forward to learning about your solutions. Enough from me on that subject, but do keep a little redundancy in the mast length, if you can.

Out of interest, would you please, when you get a moment, describe your mast (how it is made, how it was extended etc.)? And the bury, looks to be about 10%, is that right?

Moving on to the “Next Step” part of your thread. As Slieve developed his ideas, from Poppy through to Amiina’s second sail, he has progressively increased the jib cambers and sheeting angle, and he wrote: “As to whether it is better than the earlier figures we cannot be sure, but in theory it should be better and there are no stalling problems. Even with the 'blunter' entry the boat still points well so there must be more 'upwash' which is desirable, and there seems to be more drive into a seaway. If building another rig for myself I would certainly be looking at even increasing these numbers, but for the moment these numbers are known to work well.”

Regarding the mains cambers, he wrote: “… , it is normal practice for the main to have less camber than the jibs…”

This suggests to me that there may be room for some further development, and Slieve is the person I would go to with ideas. Maybe Slieve or Scott D will chime in here. Or, Robert S. and others who also have been developing this rig.

Slot width, as you say, is rather easily altered on these sails, if you allow for it when you make the battens. Don’t forget though, if you alter slot width you are also altering the geometric so-called "balance" of the sail. In fact, any of the changes you might make, are likely to affect that elusive actual aerodynamic centre of pressure of the sail as a whole – whatever you do, that has to stay aft of the mast (axis of rotation of the rig), sail balance being exactly what we don't want.

Your "37%" point of maximum camber: I guess there are people with theoretical knowledge who can comment on that. (see "aerofoil shapes and entry angles" including a delightful post from Arne on 25th April). I drew my aerofoil more or less freehand and I think that the maximum point was about there - by the time I had made the pattern and sewed the sail I am not quite sure if it was still there though! You realise, of course, your soft fabric sail when inflated will not end up looking exactly like the stiff paper model.

We should also probably at this point remind ourselves of a common sense statement made by Arne in the thread referred to above, to the effect that this is not rocket science and people should not be put off making their own sails, from these hypothetical discussions which are so interesting to some people and maybe not so to others.

You are at the cutting edge Robert. The beauty of these little home-made sails is that we can afford to “suck it and see.”

And down in the garden where you have set up your model - I expect you will be planting a row of runner beans there next spring?

I think most people will agree with Scott in all his reasons given - and bearing in mind this little junk rig is scaled down from the diagrams we are normally used to looking at, your latest version looks to me to be a much more practical and workmanlike arrangement for a small boat. Well done.

Have you made your mast yet? If not then you might want to allow a little extra height - either that or shorten your sail plan a little. I did the same thing as you are doing and designed a mast and sail with a view to trying to get every square inch of sail possible onto a mast which was as long as I dared to make it. The result was, just not quite enough room up there between yard and masthead. As it happened the mast was a  bit longer than planned and buried deeply in a sunk tabernacle, and I had not quite got around to cutting it shorter - so I had a way out. I have now a rig which is perhaps a little too big, we will see - but luckily at least it works. 

You say that there is 0.6m of mast above the yard - but it doesn't seem to look quite right - and putting a ruler on the computer screen makes me think it is a little bit less than that, and at best, barely enough. The sail is almost brushing the deck, and if it turns out you do need a bit more halyard drift, then you have cut things so fine you might have nowhere to go. (I was previously thinking to myself that you always had the option of cutting off the bottom panel later, but with your improved sail you no longer have that available as a plan B.)

Here is a thread from a few months ago that might be useful for you if you haven't already noticed it (minimum preferred mast height) and look especially at David T.'s typically lucid advice on this, which he posted on 27th March. His final comment: "But if possible, it's better to go for more than the absolute minimum drift that the blocks can tolerate." If you want to cut things fine, I will add that drift is not measured from the mast head. David's words again: "that drift being measured between the attachment points on yard and mast."

Here is where I came unstuck: on a small boat you also need to remember to allow for the sail to be able to hang in the lazy jacks with the halyard released, with good clearance remaining for the sail to swing clear of the deck and/or tabernacle. With your boom just clearing the foredeck, your proposed sail plan is therefore showing the sail in taut lazyjacks (if they are the standing variety), and needs the potential to be hoisted a little higher with the halyard. You might have to try out a few different arrangements before you are satisfied with your halyard and lazyjacks. If you want running lazyjacks (as suggested by Dave D.) there is a couple more blocks and I haven't properly figured out a yard hauling parrel for mine yet, so there's another block which might have to fit in there somewhere too. There is not much room up there on a small mast, and the whole contraption has got to be able to rotate easily as well as just be hoisted.

I suppose this is all so obvious to experienced junk sailors that it seems hardly worth mentioning. But not having done it before, and thinking I knew more than I really did, it was a trap I fell into. So, give yourself just a little bit more wriggle room is my suggestion. Your Pathfinder is going to be a great little conversion.