thanks mike. very clear.

this is the first i've heard of light-wind steering problems. do any of the visionarrys lose control like this? is there something different about the shape of the 18m hulls or rudders that can explain?

rick: i'm very interested in the wrong-way polars. what software do you use to make them?

neutral helm seems very slow to me, as the rudders then don't counteract leeway. with independent rudders, one can use the aft one to counter weather helm, and the forward for lee helm. either way shifts the sideslip drag from the low-aspect inefficient hull to a high-aspect foil.

ben

--- In harryproa@yahoogroups.com.au, Mike Crawford <mcrawf@...> wrote:
>
> 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