Anonymous wrote:

Yes, Jes, I think you are overthinking a bit.
The odd-looking number 1.98, has nothing to do with me being particularly accurate or bright. The number is just there to point you to the corresponding master sailplan

Ten years ago I produced a string of master sails, called the Johanna style master sails, with AR rising from 1.80 to 2.25 with 0.05 increments, and all with 70° yard angle. Only recently did I design a string of master sails with yard angles at 65 and 60°.

To make them, I started with the ‘Johanna 70’ master sails.
I kept the four lower panels and made new 3-panel top sections, doing my best to make the area of these top panels almost the same as in the lower panels.

I stick with the method in PJR for finding the AR: AR= h/chord, where h is the vertical height from peak to boom. In your case, this Johanna 60sail with AR=1.98 is thus a result of the Johanna 70 master’s  with AR = 2.00.

This is how I go about to find a suitable rig for a boat like yours.

• ·         I start with drawing a vertical mast line where the mast is supposed to go.
• ·         Then I draw a long boom line with 10° rise.
• ·         Then I play with this formula to find a possible combination of batten length and AR which gives the wanted sail area and a usable mast balance.
  SA = B x B x AR x 0.78. This formula hits within one sqm, but remember to, in this case, put AR = 2.00 into the formula.
• ·         In your case I end up with a 60° yard to allow a hi-balance sail to sit.
• ·         Then I go to the string of Johanna 60 master sails (found und MASTER SAILPLANS here: The Junk Rig Association - Arne Kverneland ) and pick the one with AR= 1.98. A quick check with the calculator make sure that the area will be right.
• ·         From the two sheets of that master sailplans you can decide how much camber you want (I use 8%) and by reading Chapter 4, find the right numbers for the needed Round, R.

Clear as mud, right?

Arne

Arne that's great thanks, it will be clear once I've gone through it all!!  I've just bought a sewing machine off ebay and sent off for some sailcloth samples and a roll of paper for llofting .  Will probably make a start sometime in the new year.

Anonymous wrote:

This summer JRA member Paul Schnabel has successfully cruised his Maxi 77 with his junkrig set with up to 27% mast balance.
I have therefore made use of his findings and drawn a hi-balance sail for the Corribee, shown below.

The mast was put through the hatch, with its centre about 200mm aft of its forward edge.

I don’t think the sail will ever need to be moved forward of the shown position. If anything, it rather needs to be shifted aft a little to trim away any lee helm. There will be plenty of room for that.

The Corribee has a smallish rudder. This hi-balance JR brings its CE quite close to the JR mast, which again means that the CE will sit close to the boat’s centreline when sailing downwind. This should help the rudder to cope.

Just an idea.

Arne

PS:
It looks to me that the superstructure of the Mk 2 and 3 are very similar, so I used a Mk 3 version here.

(Hi-res diagram in Arne's sketches, section 8, photo11)

Hi Arne, can you explain to me why you chose an AR of 1.98 for this sail.  I am working my way through understanding the sail design. I have printed off Chaptre 5, Making the Sail.  For convenience sake I could use the AR 1.95 drawing and scale down the dimensions of that design to draw my sail but I would lose about 1sqm of sail area, or I could go up to the AR 2.00.  I don't suppose it would make that much difference. May be I'm overthinking it, certainly doing a lot of thinking!!

Anonymous wrote:

Anonymous wrote:

What about having a closed pocket at the luff and just tensioning at the leech, or vice versa?  Is it better to make plugs for the batten ends or just use ring bolts or similar to tie into?

I have these closed pockets at the leech of my sail, to prevent the battens to catch the sheetlets. They are closed  with webbing, and I have used wooden plugs at each end of the aluminium battens. At the luff I have webbings with velcro to tension the sail. So far I'm pleased with that system.

Thanks, that's interesting. What sailcloth did you use for your sail?

With the mast ordered I have started to look at yard, battens and boom. I am planning to use aluminium tube, From PJR there is an example of batten size of 22mm x 3,2mm used for Pilmer which I have used as a guide. I have chosen a bigger dia tube for the yard in view of the weight it carries, and a slightly bigger dia tube for the boom so that it doesn't bend with the pull of the tackline.   I am thinking of:

Yard      40mm x 5 or 3mm wall thickness

Battens  22mm x  3.25mm wall thickness

Boom     28.5 x 3.25mm wall thickness

Do these sizes seem about right?

I am interested to understand how the battens are tied into the sail. It seems they are often tied/tensioned at both ends. What about having a closed pocket at the luff and just tensioning at the leech, or vice versa?  Is it better to make plugs for the batten ends or just use ring bolts or similar to tie into?

Thanks for any comments/suggestions, Jes

.  

Anonymous wrote:

I've found this...looks like it could work.  It's 7m tall in total, 3mm wall thickness, tapered starting 2.8 m from the bottom, from 145 to 76mm dia, so would need a small extension according to Arne's sketch, which I think is 7.7m in total. I don't know how the access door would affect strength.  I could weld it to seal it and strengthen that area.

- Jes

Jes, it would be a pitty to buy a mast weakened by any holes. Even if welded shut, those areas will be where fatigue appears first.

It might work for you to directly contact that supplier, and ask them if they would sell you the raw mast - of a production stage, where they did not cut any holes yet. At least, that worked out when I bought the mast for Ilvy. It was cheaper, too.

Cheers,

Paul

So the exciting news is that I've managed to get the company to supply this pole with no cut outs or holes, just a plain tapered tube!  Delivery will be in the new year.