Aerojunk Coromandel

In 2015, Gavin Dalglish put me in touch with Paul McKay, who had sent him designs for an aerojunk rig for the Coromandel. I’ve just managed to get back in touch with Paul, who’s given me permission to reproduce his drawings and documentation here. I thought it was timely given the discussion of Emmelène’s split rig, and the sudden burgeoning of aerojunk rigs by Pete Hill and others in the JRA Magazine issue 74. I’d much rather have this somewhere public and useful than sitting in my inbox!

Here is one of Paul’s drawings, over the top of the standard rigging of the Coromandel.

There’s more complete information in Paul’s document, AeroJunk Folio Interim 2.  In addition, Paul wrote to Gavin:

I have drawn a suggested AeroJunk sail plan for your boat. I have overdrawn it on an original line drawing from Newbridge for comparison. You can see it is semi-elliptical. The original ‘lead’ appears to be 7.5%. This design will give a ‘lead’ of 10.25%. If there is a problem with weather-helm or too small a rudder then this will help a lot. Hasler/McLeod allow for a lead up to 12%.

The position of the original C/E and the position of your mast determines that this AeroJunk design becomes ‘low-aspect’. (My mast is further aft and forces a high-aspect design) The new C/E will be lower than Newbridge’s, so although this sail is 199 ft2 or 18.4m2, you should be able to carry the extra sail without penalty. Because of the camber in both sails it should go like a train!

I have drawn a batten angle of 1.5% above the horizontal. This works nicely on my boat. The batten spacing is 3ft or 915mm. The batten width will be such that the main produces a 1:8 camber. I haven’t worked this out yet but the boom will be somewhere between 600 and 900mm wide at the mast. You will need a spreader yoke about 400mm wide hung just below the front mast top. The lazy-jacks will be fitted to eyelets at 350mm centres on this yoke. Although the jib looks narrow it is slightly larger than mine so will work well.

Because of the low-aspect, there will be no problems with jib/main balance. Finally I have drawn a deliberate roach at the top of the mainsail. I suggest you incorporate that by fitting short permanent battens to support the roach. If you do away with the roach you will increase the ‘lead’ slightly. Something you can try if you still have weather-helm problems.

Gavin was planning to build this rig, but I have not yet managed to get in touch with him to find out how it went.  The last I heard, Gavin was drying out his Coromandel for osmosis treatment somewhere near Vannes in Brittany.

Here is a picture of Paul’s Etap 23i with a similar rig. Note the different sheet arrangement.


Paul wrote to Gavin:

Having finished my batten remodelling I took the boat out for a sail on Tuesday. It was a perfect Force 3 wind and I got a broad reach from just outside the marina for two miles before I had to tack. I was getting between 5 and 5.5knots. The tack took me close hauled and I still got 5.5kn although I was well heeled over by this time. That close to the wind I have the rudder hauled towards me as the weather-helm naturally increases. But this demonstrates how efficient the AeroJunk can be. My waterline length is 19 feet compared to your 16 feet so my maximum hull speed is 5.66 knots but I have had the boat at 7.5kn downwind. This is with 208ft2 sail. (Well down on the supplied sail area although the official sail area is 196ft2)

In a later message to me, Paul wrote:

Because the top weight of this rig is lighter than a conventional junk I use a downhaul line fastened to the main halyard/sail cringle. I need this to get the last 2 panels down so a combination of pulling the mainsheet and the downhaul does the job.

As Gavin says the forward mounted cockpit sheet jammer and the sheet fastening to the tail of the halyard presses the battens in against the mast and helps to reduce twist in the sail. Because of the twist in the sail, in an Ocean-going boat, I would use heavier canvass and a flatter camber in the top panel that would double as a storm sail. My rig, now 204ft2 (18.95m2) is made from 5oz Dacron.

To keep the sail tidy and effective when reefed I use individual downhauls on battens 1 and 2 plus a combination downhaul fastened to the front of the boom, batten 1 and 2. These have been good enough for up to a Force 5 wind. The strongest wind I have sailed in was a F5 (forecast 19mph) You could have a downhaul for every batten if you had enough deck sail clutches.

I suffered a blue-sky knockdown last year when hit by a gust on a sunny day. I think I got to about 50 degrees heel. The gust spun the boat round in its length while I hung grimly on to the safety rail. The whole thing lasted about 20 seconds. I estimated later it to be a Force 7 with all sail standing. The only effect was to stretch 4 of the 50lb locking cable ties.

Today, Paul wrote to me:

I am just about to start [a folio on the Aerojunk] again. I have also just designed a new sail for Miranda, slightly larger at 20m2 and have made new battens from telescoping aluminium tubes. The sail is being made now and I expect to get it in a couple of weeks.

It was interesting to discover that Pete Hill had made AeroJunk sails for his new boat, Oryx. I believe he has now designed and made AeroJunk sails for 2 other boats in New Zealand. He has done this without any reference to me so must have got all his information from my original articles in the JRA Newsletters. […]

When I finish the folio I will hopefully publish it in the JRA.

So we can look forward to some very interesting updates from Paul. In the meantime, this article will I hope encourage and interest you all.


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4 responses to “Aerojunk Coromandel

  1. Antoine Maartens

    Paul sent me this drawing too. Very interesting! A bit more high tech than Pete Hill’s incarnation of Paul’s original idea I think. Great work and original thinking – I admire both of them.

    From what I read on Pete’s take on this idea, the sails are completely flat and make for easy sailmaking. Must say that I very much like the bulletproof workings of the mainsheet when reefing on the HM setup. Just pulling the sheet and thus locking the panels down makes perfect sense to me.

    Don’t know how that would work in this very beautiful setup. Paul’s setup clearly has looks on it’s side as far as I am concerned.

    • Robustness and maintainability are high on my list of requirements, but that doesn’t necessarily rule out wishbone battens. I’d definitely prefer flat cloth, though, because I can sew it myself.

      Paul made two drawings with different sheeting arrangements. The one above is similar to HM. The photo shows the other.

      • Antoine Maartens

        Really think this is the way forward on our boats – more so than Arne’s setup. Because of how far back the mast is. Wishbones don’t worry me at all. Flat sails – same thoughts here. That makes me prefer this over Slieve’s setup.

  2. Pingback: The Spitfire sail | Tammy Norie

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