I noticed this over-balancing phenomenon on Edward Hooper's Amiina, when I sailed on her from Poole to Lymington, and I recommended to Edward that the rig be moved further aft on the mast. I felt it to be most unsafe on a boat of that size that I would let go the sheet in a gust, and the sail would not feather to the wind.

Hi Thierry, no. In all cases the mainsail remains at 160ft2. This next combination will have a 46ft2 jib so my total sail area will have dropped to 206ft2. The odd thing is that the boat goes well without the extra area. Perhaps it only needs more sail if you want to go racing.

AeroJunk Update

I could not have chosen a better year to develop a new rig. Here on the West of Scotland we have been blessed with weeks of sunny weather and mostly S/W winds, Force 1-3.

I got Miranda kitted out and launched then tried the first sail in a Force 1. My rig measured 246 ft 2, exactly the same as the original Etap 23 rig of Main and Genoa. My jib equalled 34% of the area of the whole rig. The sail set to near perfection with the ideal aero-foil profiles. We were the only boat sailing, all the Bermudans were motoring and we were getting 2.5knots. Then the wind gusted to 2/3. Instead of weathercocking the sail swung broadside to the wind and the boat heeled sharply. I panicked and dropped the rig by 2 of the 7 panels. We spent the rest of the afternoon with 5 panels and the boat sailing itself with the sheet hanging slack so all I had to do was steer. This was fascinating but weird. After all, I had lost one of the natural fail-safes. It appears that my 34% jib was producing as much power as my 66% main.

This puzzled me and I needed a boat that was safe to sail so I made a temporary smaller jib from PolyTarp which measured 26% of the total area. I subsequently tried it in a Force 2/3 wind. Once again the rig performed perfectly getting 5.1Kn downwind and 4.5 on a broad reach. However when the wind gusted to 4 the whole rig turned broadside and the boat lurched over again. My jib was obviously still too large.

I based my sail percentages on the original AeroRig and split junks that seem to balance with 30-33% in the Jib. I puzzled over this for a week or so before coming the following conclusion.
If you observe a split-junk from behind the 'slot' or vent between jiblet and main forms part of a circle. If you observe the AeroJunk from behind the 'slot' is a rectangle. By rough calculation my rectangle is 25% larger than the part/circle vent. Ergo, my jib is 25% more efficient than the jiblets on split junks, ergo I need to reduce the ratio of my jib/main by 25% of the whole to 22.5/77.5%.

So I have re-cut my temporary jib again down to 22.5% and will fit it later this week and try again. I also have other experiments with halyard, sheeting and downhauls to try but the main thing is the rig works, and works well and I now know it is just a matter of balance.

Watch this space!

Paul McKay