Ben,
The rounding-up issue, particularly on a rig with one sail, would
stem from two different forces:
1) The weather helm caused by the COE of the rig being aft of
the CLR created by the rudders/hulls.
2) The weather helm caused drag of the windward hull.
In really light wind, particularly with rudders that aren't that
deep, these two forces added together could require enough helm to
nearly stall the boat. There just isn't enough flow over the foils
to let them do their job without angles large enough to create a
stall.
But if you put the leeward hull to windward, the ww hull will try
to twist the boat off the wind, creating a lee helm, which will
counter the weather helm caused by the rig. As a result, the
rudders could be almost at neutral, which could be quite significant
at low speeds where flow over the rudders isn't that great.
I never would have thought of this on my own, and when Rick first
described the effect, it didn't make sense. But as Todd is fond of
saying, experience is worth at least as much as theory.
It looks like this is a nice way to balance things out at low
speeds.
- Mike
bjarthur123 wrote:
rick,
i think what you're trying to say is that the polar for light winds might be such that the best VMG to weather is made for less than 2.5 kts boat speed, and if you try to go that slow with the rig to lee then you'll go into irons.
it seems to me, however, that if the rudders are ineffective at slow speeds, they will be ineffective no matter which way the wind blows over the boat. if the rig is to lee you'll go into irons; if it's to weather you'll bear away. either way, you won't be able to maintain the best upwind VMG speed or angle. no?
sure, you'll be able to temporarily pinch with the rig to weather. but it's only faster because you reduce the likelihood that minutes will be added to your finish time while idling in irons. not because you're able to sail a better VMG.
ben_