my concern is not so much with SA/D, but rather having a sail plan which is suited to the drastically different needs of upwind vs downwind points of sail.
for any given true wind, the apparent wind is lighter going downwind. (don't mean to be pedantic here, just want to be explicit.) so you want more sail area then to compensate.
furthermore, the sail's drag points aft when close-hauled, is hence bad, and so L/D should be optimized in sail shape. whereas going downwind the drag points sideways (broad reach) or even forward (running), so is less of a concern (and even good), and sail shape should hence optimize for just L.
both these points argue for having a specialized sail which is deployed for downwind work. a spinnaker! double your sail area for the lighter apparent; a deep camber to maximize lift. combined with the great L/D of a unarig, instead of a ballestron, and you'd have an adjustable sailplan optimized for all conditions.
rob suggested just having a bigger mainsail and reefing it appropriately upwind. simpler, yes, but a lot more weight aloft. awhile back he also mentioned a junk-rig like way of adjusting the camber. that'd be way cool, but is yet untested to my knowledge. spinnakers on the other hand have a long history and have been very refined by the racers.
the wyliecat has a similar rig to the harryproa. unstayed carbon mast with a unarig. by all accounts they are lightening fast upwind, keeping up with full-on race boats twice their length. and are slow as pigs downwind. by inference i think the same might be true of harryproas. sure would be nice to have more race reports from current owners.
true, the most important point of sail to design to is close-hauled. not only is going upwind less pleasant, so you want to make the boat fast in that direction to minimize the amount of time you spend there. but there is the safety in the ability to keep away from lee shores in a storm to consider. so i'm very glad that harryproas are designed with that in mind.
but if all it takes to improve downwind performance is to throw up a spinnaker, then sign me up! the vast amount of cruising is downwind, routes purposely chosen to be so. an asymmetric spinnaker, without a pole, is not that difficult. they can be doused with a furler or a sock. it's just a matter of getting the sheeting angle right and designing the beams to take the load of the tack.
ben
--- In harryproa@yahoogroups.com.au, Mike Crawford <mcrawf@...> wrote:
>
> For the sake of discussion:
>
> a) What SA/D do you think you would need for ocean passages?
>
> b) If you want a monster SA/D, would that be for very low-wind
> conditions, or for all-out racing in higher winds (with enough crew to
> handle the challenges brought on by carrying too much sail when things
> change)?
>
> Honest questions -- whatever you feel you need is what you need. I'm
> not here to tell you what you should want. Once we know the goal, then
> we can figure out how to achieve it with a combination of sails.
>
> For convenience: http://www.nuomo.com/boatSadBruceCalculator.htm
>
> - Mike