Trapeze and spi halyard at the mast top would work
While I'm not designing to include a trapeze, I'm sure one can be fitted nevertheless. No components will fail but I also make no guarantees that the sail shape or sailing behavior will be optimal. I feel that I can about guarentee that with the asymmetric spinnaker.
A topmast asymetric would be big, but a bridle or shorter pole would bring the area back to normal.
About 12.5 sq. mtr. I think ; if we maximize it.
The pole takes only longitudinal (compression) loads, while the bridles take the lateral ones. If the pole isn't longer than the bow, the effort in the bridles should be the same with or without pole.
You overlook the sheet and tack halyard loads here; the ones that pull the tack the spi sail and therefore any bridles backward. Ergo one can not simply remove the pole (even if it did not go past the bows) and assume the bridles will see the same laods or even stay in the same place.
The Swell Shadow catamaran has a pole less design but needs an additional line coming of the forestay (which are fitted to the bows in this case) to stabilize the spi bridle. See the attached picture. My design doesn't have a fore stay and adding one is more complex then simply adding a spi pole, which in my design is incidently the same as the mainsail boom. Not having a forestay reduces the stresses placed on the bows and allows for lighter and simpler construction of the hulls. It is also one thing less to pay for or worry about.
This pole-less setup will pull the spi bridle well back from the bow, closing off the opening between the spi sail luff and the mainsail luff. The end result is a much reduced overall sail area for the spi; more like at max 5 sq. mtr. And lets not to forget the web of lines on the front of the boat. Neither looks nice or is it easy to rig. The pole setup is better in the achievable area, in the spi-to-mainsail slot and in construction.
Wouter
