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

bjarthur123 wrote:

 

i've changed the title on this old "bow down attitude" thread to a new idea i'd like feedback on. the clip below is of my previous suggestion to tack an asymmetric spinnaker to the leeward hull on a unarig. the problem is a good sheeting angle for the clew.

what about tacking an asymmetric spinnaker to the forward beam halfway between the hulls, or even closer to the windward hull? sheeting to the leeward hull near the aft beam should then provide a good angle.

in heavy conditions you could just take the main down and go under spin alone. the same sail area, with a deeper camber, would yield more forward drive, and as we discussed recently with rick, depress the bows less.

in light conditions the spin and mainsail could collectively be thought of as a two-element soft wing.

think of the hard wing on the new america's cup catamarans. the first element is "tacked" to the center of the forward beam and "sheeted" out a bit. there is a slot between the two elements which helps maintain laminar flow. the second element is kept parallel to the hulls, such that the "exhaust" vector is straight aft.

ditto for what i propose here on a harryproa. the asym spin is the first element. there is a slot. the main is the second element, and is sheeted to the centerline of the leeward hull.

whereas upwind on a unarig with the spin in the bag, the main would be sheeted a bit off the centerline, like a bermudan jib, like A-cats and wyliecats do; downwind the deployed spin alters the angle of the airflow to the main, so you'd sheet the main further *in*, at least relative to where it would be without the spin, or with the mast stepped straight aft of the spin tack.

i believe this passes the simplicity test, and solves the under-powered off-the-wind problem. again, not for buoy races, but ocean passages. make sense?

and yes, the weta spin (or gennaker as we call it; it's cut pretty flat so it can be furled) is one-design.

ben

--- In harryproa@yahoogroups.com.au, Rob Denney <harryproa@...> wrote:
> > what would you think of an asymmetric spinnaker tacked to the forward beam
> > where it inserts into the leeward hull, and sheeted to a similar spot aft?
> > on a unarig. that should be good for 90 degrees apparent. the stresses are
> > all still concentrated in the lee hull between the beams. the COE is moved
> > forward so you have less weather helm, which is faster off the wind. the
> > top of the mast is pulled forward, adding more camber to the main, which
> > increases lift and is hence faster off the wind. i'm thinking ocean
> > passages here, not buoy races, so if you have to take it down to gybe, no
> > big deal. just not sure the sheeting angle would work.
> >
>
> Me too. Could sheet it to the end of the boom. Could also beef up the
> hull and fit some means of pulling a genoa tack out to the ends. No
> shortage of possibilities depending on what the boat will be used for, but
> my preference is usually for lightest, simplest and cheapest.

> Is the Weta spi one design?