lets not get too technical Wouter, if it is kept as a simple two dimensional graphic, it will suit for the purpose of illustration for a "visual" calculation that will show a reasonable representation of where his centre of effort is that will in turn help him to determine it's rtelationship to the centre of lateral resistance of his hulls and from that the understanding of how adjustments can be made to balance the two on different points of sail by all sorts of "set ups" ie mast rake, crew position for different points of sail, cemtreboards raised or lowered for different points of sail and different combinations of sails, etc, etc, and the use of his hulls "shared resistance with his centre boards and rudders, to leeward drift (or shared lift -as Bill may say-)" Or as I tend to say, "keep the leeward hull deep to counter any extravegant lee (or windward) drift, and the windward hull just free of the water.