thanks for the info rick.

i understand how sailing with the rig to windward keeps the boat keep out of irons when the rudders are on the verge of stalling in light air. the drag of the ama counterbalances the weather helm caused by the aft COE of the sail instead of adding to it.

it seems to me though that, even if VMG is not better sailing with the rig to windward, that there is another benefit to having a boat which can sail the wrong way around, specifically in (1) short-course W/L buoy racing and (2) long narrow channels.

in light or heavy winds you don't have a choice, and would generally want to always sail with the rig to windward and leeward, respectively, and hence shunt. but in moderate winds one could tack/gybe ones way up/down the course/channel instead. i would have to think that that would be faster, as one doesn't completely lose all forward momentum during a tack or gybe as one does during a shunt.

does it make sense then to design the boat from the start to be able to sail in light to moderate winds with the rig to windward? and if so, how would the design be different from a boat that was meant to always sail with the rig to lee, if at all?

ben

--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
>
> Ben
> I did it but cannot recall if I published the comparison. There was
> not much difference in the polars. VMG does not change measurably.
>
> From a sailing perspective having ww hull to lee is significant
> benefit in light winds because the boat automatically bears away when
> the rudders stall so it is self-correcting. Sailing ww hull to
> windward the boat rounds up when they stall and there is no way to
> recover other than shunting out of it.
>
> The rudders stall around 2.5kts sailing either way around. In 5kt
> wind that occurs at 50 degrees to true wind. In present form with
> the two 900mm deep rudders the best VMG is at 55 degrees. So there
> is 5 degrees to play with. Momentary lack of concentration, wind
> shift or wave can cause it to round up.
>
> In practice it is very easy to sail it at best VMG with ww hull to
> lee. With ww hull to windward it needs to be sailed freer than best
> VMG to avoid rounding up.
>
> The polars show where the rudders stall and the angle for best VMG
> but they do not show the consequence of stalling the rudders.
>
> The other factor I have not yet included in the VPP is the loss of
> span efficiency when the rudders lose the end-plate effect of the
> hull due to it being round section. This is most noticeable when
> sailing faster because there is a position of instability compounded
> by backlash in the two gearboxes in the steering linkages.
>
> I have done a number of comparisons for different rudders and
> concluded that going to 1.2m deep but shorter and thicker would
> improve windward performance. However that does not completely
> overcome the rounding up issue but it occurs closer to the wind.
>
> The rounding-up issue is simply something to be aware of. We have
> made lots of "Z" patterns over the Bay trying to sail to windward by
> getting in irons and needing to back out. It is nowhere near as
> inconvenient as trying to get some beach cats to tack through the
> wind - they are not intended to go backwards. This nuance with the
> proa is a blessing in light winds with ww hull to lee because the
> boat essentially sails itself.
>
> Rick