Actually the 3D situation on sailboats is a very interesting one.

Even far ago designers knew about this issue/problem. The large schooners and such of two centuries ago were designed to be sailing with a minimal heel. The desired amount of weatherhelm was designed into the craft at that heel. This left the problematic situation where in very light winds (almost no heel) the boat would have leehelm on all courses including going to weather. To combat this the top sails were invented. These are the relatively small sail all the way at the top of the mast. Often tensioned between the mast top and the top Ra (English translation ?). These are not at all intented to provide propulsion but to induce heel so that the craft would return to its design sailing behaviour. Of course any extra propulsion provided would be welcomed by the main goal was extra heel and this was the main criteria of wether to deploy these sails or not.

Also Breaching on a mono hull can only be fully explained by a 3D situation. And as a matter of fact it is a desired characteristic. It is used on mono's as an extra safety mode.

You see how important 3D considerations can be ?

Wouter