K/proa

The 1st iteration stepped the mast on the outrigger hull and employed two boomed headsails. The two hulls were equal in length and spaced apart 80% of LOA. The hulls were lightweight and had little reserve buoyancy so that any upward or downward directed forces generated by the various sail arrangements were clearly visible.

I had learned on Model No.1 that one needs to ensure that the sail's total lift vector, projected back to windward, goes between the keel/rudders. When this projected line was estimated to be about one-third to one-half of the distance forward of the aft keel/rudder, the models self-steered nicely. When the vector fell aft of the aft keel/rudder, they turned into the wind and couldn't be made to fall off. It was also learned that, when located at the bow on the outrigger hull, the sail need not be sheeted in tight for self-steering and the boom could be let out about 30 degrees before steering problems arose.

With the goal of lowering the sail's center of lift and improving upwind performance by increasing the L/D ratio, a variety of decks (end plates) were installed beneath the sail. These had an undetermined effect of performance. I couldn't tell if they helped or not, due to the large wind gradient affecting a small sail so close to the water's surface. The wind gradient also required the sail to be inclined more to windward than would be the case on a man-carrying boat.

	The 3rd iteration sailed excellently. All forces were in balance and both hulls remained level on the water. In spite of its spindly intra-hull connections, there was no noticeable bending of the long dowels. Because there is a vertical component in the sail's lift, in a strong wind, the bows lifted and the model planed across the water.

	As the design is intended for fast passenger and cargo carrying, I was concerned with real-world construction and operating cost considerations. I wanted to use a sail that was flat (bi-directional and easy to make without sewn-in curvature) with high L/D at low angles of attack, so I settled on a single, big jib.