Using a tension adjuster like in the photo on the A can be worthwhile as they need the extra power downwind. Spi boats dont want an extra full mainsail going downwind, we want to keep the slot open.
That is what my model says as well.
The A-cats can accept larger induced drag forces when they are beating downwind as their apparent wind angle (over the mainsail) is alot more perpendicular to the direction of the boat. Here the drag is not trying to slow the boat down anymore but rather trying to push it to the side. A direction that is easily resisted by the daggerboards against a very small in-line drag penalty.
F16's however with the spi tend to have the apparent wind over their mainsail rotated much more along the centreline of the boat so any increase in induced drag is immediately transformed in in-line drag and will try to slow the boat down. In most case it will therefor be better to keep the mainsail breathing freely with a relatively low draft to cut down on induced drag. Exactly the same as when going upwind.
Up till now everything makes sense.
Wouter
