Downwind in Light Air
The questions are many:
Should I sail by-the-lee like a Laser?
Should I broad reach?
What angle should I sail off the rhumb line?
Should I S-Turn?
How much should I heel the boat to weather?
How can I get comfortable and remain mobile?
How can I stop the lurch to windward?
How should I sail an Aero downwind in light air?
We're all learning how to sail an Aero and our experience base is pretty small at this stage. So these comments will definitely need to evolve as we gain more experience. So if you discover that something different that works, then you are probably right too.
For this posting, I'll define light air as under 8-9 knots and I'll assume the water is relatively flat with little or no waves.
What Course to Sail?
You have a choice downwind: you can sail straight downwind, sail at a slight broad reach, or sail by the lee with the flow reversed across the sail from the leach to the mast. Sailing straight downwind is pretty slow. You have poor flow over the sail. Sailing by the lee or a slight broad reach is faster.
I've found that sailing by the lee seems faster than broad reaching in light air, but balancing the boat is a bit trickier. Broad reaching seems to work better when the wind is up a little more — so if there are gusts above 8-10 knots, then broad reaching can work well. And, you can switch from by the lee in the lulls to broad reaching in the gusts.
Be a Smooth Operator
It is imperative that you be smooth in all your movements. Shaking the sail and the boat is definitely slow.
If you need to gybe, make sure you do a roll gybe that will pop the top batten as part of the maneuver. If you have to pop the batten after gybing, that will shake the sail and boat and can be quite slow.
Don't Drag Your Butt
While sitting in the center of the cockpit may be comfortable, it drags the stern and is slow. You need to be forward, right next to the centerboard. In light air, move as far forward in the cockpit as you can. In fact, it is better if you can get your front knee forward of the cockpit beside the centerboard.
Here is a posture that I find comfortable and stable:
No, not that posture, this one:
I'm right at the front of the cockpit and my front knee is beside the centerboard. I'm seated inside the cockpit and not on the deck topsides. That is essential otherwise you have too much weight to weather and the boat can (and will) lurch / death-roll to weather.
My back knee is well to leeward so I can press down to flatten the boat when required. From this position I can quickly move to leeward. Even in light air, you can get a small gust that will initiate a roll to weather. If you cannot quickly move to leeward, you may capsize to weather. Unlike a Laser, where you can correct a death-roll by steering into it (deeper by the lee), in the Aero, this technique does not work due to the hard chine. You must move your weight, like this:
Play the Sheet
The wind is never constant and varies in speed and direction constantly. When the wind is light, these changes up and down 1-4 knots in strength can easily double the wind speed. So you cannot just sit still with the mainsheet cleated. You should be constantly moving, feeling the pressure in the sail and adjusting your course and trim.
Trim from the Boom
Because the Aero has a center mainsheet, you can grab the aft two lines and have a direct 1-1 control over the mainsheet.
You can gently trim the main in response to the pressure. Be careful not to move the sheet too much. A 1-1 control requires a delicate hand. Ease the main to let the pressure build and then trim in.
If it is really light, just grab the single line from the boom to the mainsheet block as it will allow more gentle adjustment.
Play the Waves
Often there are tiny waves you can use in light air. This is the key to downwind speed in light air. If you can get a little push from these waves, you will be much faster.
The technique is very similar to that of a Laser. Let the boat heel a little more and bear away a few degrees to go deeper by the lee. This will then accelerate the boat, but you are going further from the mark. When you see a wave that may give you a push, use that speed and gently flatten the boat, trim in a little and head more downwind. This will help to accelerate the boat and get you a bigger push from the wave. You need to be careful that you are not just rocking the boat, that will break Rule 42. You need to use slow, gentle movements and turning. Note: you don't cross dead downwind, so you can think of this as a slow, gentle half-S turn.
Active Sail Leach
If you have the main trimmed correctly, the leach should flick and pump in response to the changing wind speed. As a gust hits, or a wave causes the boat to move, the leach will flex and then snap back into position. This is very fast and is a totally legal automatic pump by the rules. If you have too little vang, or too much, the leach won't flick. Watch the 2nd top batten and it should be very active. The video at the end of the post demonstrates this.
Reach in the Gusts
If you sail mostly by the lee, you will gradually get to one side of the course. Eventually you will need to get back to the mark. You can either gybe over and go by the lee again to the mark, you you can look for opportunities to broad reach.
In spots of increased pressure or if the wind shifts more to the windward side, then you can effectively transition to broad reach for while. If timed right, this can be very fast.
To transition from by the lee, roll the boat to leeward by pressing down on your leeward knee. The boat will start to turn without you having to use much or any rudder. Then trim in and flatten the boat when on your desired broad reach course. This gives you a legal pump as you turn. The Aero accelerates very quickly in a bit more pressure and the little stints of broad reaching can gain you distance and center your course at the same time.
If the wind is very light, stay sailing by the lee. Do not broad reach if the wind is square from behind. The reasons is that crossing dead-down-wind on your way to a broad reach is very slow. It is better to do a gentle oscillation from deep by the lee to build speed, and then shallow by the lee, to drive to the mark.
Putting It All Together
Respond to the conditions and constantly play the mainsheet
Catch small waves and do slow, gentle half S-turns on waves
Have an active leach
Broad Reach in the gusts
Here is a short clip sailing downwind at Shilshole Bay in Seattle. I'm sailing in a 7 rig chasing a 9 rig. The wind was about 8-9 knots, at the top end of the "light" wind spectrum, but the technique is the same. You'll see the leach of the sail is very active around 1:30 in the video.