When I designed the AeroJunk I discovered (the hard way) that 33% of the whole sail area in the jib was the limit for tall rigs. (Size of Jib compared with the Main). Lower aspect sails can be a little more. 

You can calculate the ratio between the jib and the main for Split Rigs.

measure between the C/E of the Jib and the mast centreline in Millimetres. Multiply by the area of the jib to give a factor. 

Do the same for the main sail to give another factor. Divide the smaller number by the larger number to give the ratio. Expect answers to be between 0.10 and 0.20.

0.16 - 0.195 is good. Anything more than 0.2 reduce the width of the jib. Anything smaller than 0.15 increase the area of the mainsail. Otherwise the whole sail will turn broadside in winds of Force 4 and above. 

Thomas wrote:

Arne, I was on board the other day and checked the forepeak situation with the berth. My Seal does seem to have a slightly different layout where it uses all the space for the bunk, and doesn't have the cut out space shown on the original plans that could fit a mast. So looks like a high balance rig is required for a sloop.

Thomas,

remember that you will also have to redo the L-sofa if you choose the SJR. Anyway, that is a small task compared to the whole conversion project.

You have the choice between my ‘ordinary’ cambered panel sail, a SJR, an Aero Junk or a soft wing sail. The last three sails may perform better for a given area than the Johanna-style sail (never verified).

However, the first, the last and the most important part of the rig is the mast. You have to decide how tall and heavy mast your vessel is to carry, regardless of the sail type. When that is done, it is time for choosing the rig. From what I have seen, there is no other rig which can set a bigger sail area than the Johanna style HM rig. Big is beautiful.

Moreover, these days, after the two Pauls (Thompson in NZ and Schnabel in Germany) have shown that the mast balance can be increased from my initial max. 17% to well up into the twenties, there will not be any steering issues downwind with my suggested 64sqm Johanna 60 style sail (25% mast balance)

Yes, and again, the mast height (14.15m) is probably as low as you can get away with for carrying a 64sqm sail (..yes, I rub it in...).

For a less biased opinion than mine, I suggest you look up JRA Magazine 93 and read Pete Hill’s verdict from sailing their ‘Kokachin’ (p.3).

Anyway, good luck; your Van de Stadt vessel will do fine with any rig!

Arne

Thanks everyone for their input, wonderful! More than I could have hoped for.

No pressure Slieve, I cant start doing any actual work until my house is finished and tiny house sold to fund the boat refit, probably 9 months away. There is plenty of time to do the thinking and planning.

Arne, I was on board the other day and checked the forepeak situation with the berth. My Seal does seem to have a slightly different layout where it uses all the space for the bunk, and doesn't have the cut out space shown on the original plans that could fit a mast. So looks like a high balance rig is required for a sloop.

I'm too interested in the rigid parrals of some sort. The Aero Junk solution is intriguing and I wonder if any hybrid solution like on Serenity could work at this size. I also like the look of dividing the top panel into two, especially for its use in high wind conditions, I feel (from my armchair) that the added batten would make that section more stable/supported.

The hybrid HM-SJR

I have never sailed with a SJR. However, I can read, and from a sailing point of view, it appears to work very well.

My only reason for taking the trouble and make a SJR would be that the mast position forces me to make the sail with mast balance up in the thirties.
However; I feel that the low angle yards which come with the SJR waste a good deal of sail area for a given mast height.

I have therefore rebuilt the top section of the already modified Amiina type SJR.

First step was to decide on the yard angle.
This depends on four factors:

• ·         Yard length; here it is the same as the boom and battens.
• ·         Halyard’s position on the yard, here 5% aft of the middle.
• ·         Halyard angle, here 10°.
• ·         Gross halyard drift, here 0.18 B

The resulting yard angle came out at about 48°.

From there I built up the two top panels so that batten one divides the angle between the yard and lower battens on the middle.

Finally, I removed the two upper panels from David’s 6-panel sail and moved my new section in place.

This sail will need a YHP and THP, and maybe even one or two HK parrels. Still, with more than two panels set and with these running parrels set up correctly, I see no reason why the SJR lower section should not work.

The advantage with the setup is, as said, to have more sail area for a given mast height, and, in addition, less friction due to reduced halyard angle.

NOTE: I will not recommend this big and untried rig until someone has actually built and tested it.

Regards from my armchair,
Arne

PS: I still hope to actually get to sail my Ingeborg within mid-summer. I have been on board three times; twice for coffee and a yarn, and one for firing up the outboard engine. Mr. Tohatsu delivers!

(full size diagram in Arne's sketches, section 9)

Arne wrote:

I liked David T.’s  gentle modification to the Amiina Mk.2 SJR, so now I have scaled it up and plonked onto that poor Seal 36. This puts the mast even further away from the bow.
I am unsure of where the exact fore-aft position of the sail should be. Same with mast length. Tell me what halyard angle is acceptable.

Btw. I just had a look at Martin Brown’s Custard; the latest Boat of the Month. By raising the yard angle, he has in my view solved the halyard angle issue. I guess I have to make another mod to David’s SJR...

Cheers,
Arne

Arne,

Without long-term experience of sailing with SJR, I for one am reluctant to change the yard angle and length by very much, as this was Slieve's starting point in designing low stress into the rig. I note that Poppy has a yard angle of 40˚, though, and perhaps the mk2 top panel should be split into two smaller panels, for a large rig, so as to make their leech lengths shorter. So here’s a sail that I'd be happy to take to sea. Yard angle 36˚ from the horizontal, halyard angle 15˚ and two top panels that have the same leech length as the lower panels and would be reassuringly well-behaved as mid-ocean storm canvas.