It is an observation that with the offset sail drive there is better control in light winds if the boat is sailed opposite to intended way. Conventional sail boats give two options - port or starboard tack. And both are reasonably balanced in light air. With a harryproa there are four options - two with lee helm and two with weather helm.
This boat with existing rudders, 1m deep and 0.4m chord, cannot be sailed slower to weather than 2.5kts with wind over the ww hull. It just rounds up and is in irons until the sail is backed and the boat reversed out of irons. Going to weather in windspeed below 5kts can only be done reliably by sailing with wind coming over the lw hull.
It is simply a practical way to sail the boat in light wind. We were holding between 4 to 5kts making less than 40 degrees to true wind sailing the wrong way around. (I have the GPS track and wind direction from doppler radar but there is a time shift and it is too good to be true - that said we were sailing faster and possibly higher than a modern cruising cat and 30+ft keel boat.) In the same conditions we made 3 attempts to sail to windward with the lw hull on the lee side. Speed was between 2 to 3kts but inevitably there would be a wind shift or loss of concentration and the boat would round up. We gave up beating and just sailed off the wind. By that stage the wind had picked up a bit to average about 7kts and we were making 6 to 7kts reaching. If the boat could be sailed in both directions we would have been better off sailing with the ww hull on the lee side on both tacks. However the current rudder set up with chain makes bi-directional sailing dicey.
If the mast was stepped more centrally (on the bridge deck rather than lw hull) then the weather helm could be eliminated but the wide open space of the bridge deck would be reduced.
Arguably the strong weather helm when sailing normal way around is a safety feature. Also there is a strong tendency for the lw to stay downwind with the mast stepped in the lw hull..
With a beach cat it is possible to unload the windward hull when beating in light air by moving weight onto the lee hull. Loading one hull reduces drag. This is not possible with typical cruising cat unless you have large crew or movable ballast. With a harryproa it makes sense in light air to unload the lighter hull and maximise the load on the heavier hull, which is usually the ww hull.
The 18m proa was not intended to sail with the ww hull on the lee side but it works well for light conditions. The jib only has tell-tales on one side and this makes trimming a bit more difficult when sailing the wrong way but is something that could be fixed easily.
Having two different hulls and being able to sail both ways gives more boat tuning options. We have now found the fastest way of going to windward in light air with a harryproa. Something others could test as well.
Rick
On 31/12/2011, at 9:42 PM, LucD wrote:
Is that an argument against an asymmetric lee hull too? Luc
--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
>
...
> One other learning of note. From a performance perspective there is
> no point in having a centreboard or keel that has a lower aspect
> ratio than the rudders providing the rudders can be operated
> independently. One consideration for the job list was fitting a
> long keel and reducing the depth of the rudders - essentially aimed
> at reducing draft. My analysis showed this would seriously impair
> windward performance. Roughly 10 degree loss in pointing ability for
> the same speed.
>
> All sailing yesterday was without a centreboard because the brace has
> fatigued and no longer restrains the board laterally. Sailing the
> right way around was about the same without the board but sailing the
> wrong way around was faster without the board because steering to
> counter the lee helm gets the leading rudder working to windward.
> Once the rudders can be worked independently the leading rudder can
> be set to counter leeway, which will do it more efficiently than
> relying on the hulls.
>
> Rick
>