Hi Rolf,
If the spinnaker pole is stalilized at a mid length point, the jib tack for example, then the effective length of the pole is half the actual pole length and a smaller and lighter weight tube can be used.
If a strut tube is put in place between the jib tack at the spin pole and the intersection of the forestay bridle wires, two important options open up. One is that the forestay bridle wires can be made longer, a taller bridle, which reduces the toe-in loads on the hulls. Second the jib tack can be set at whatever height above the hull deck is desired. Longer luff sails produce more forward thrust and make the boat go faster.
If a strut, vertically downward, is installed on the underside of the pole immediately under the vertical strut connecting the top of the pole to the forestay bridle, and this strut has a tension wire connecting the lower end of the strut to the ends of the pole, then it is possible to lower the outer/forward end of the spin pole which allows a longer luff spinnaker. Again longer luff sails produce more forward thrust and make the boat go faster. The arrangement I have tried to describe here is a lower spinnaker pole and the pole can be straight under load and longer luff jibs and spinnakers can be used.
I have no idea why the Tornado class did what they did. That is their business.
Bill