Hi Bruce,
The ARC 17 is a beginner's boat, no boards, a true beach cat. It does have "shared lift" between the forward half of the hull and an oversize rudder which in actual practice could be called a steering daggerboard. The objective of this hull design was to have a "beach cat" with a better underwater lift to drag than other boardless beach cats so it would go faster and a boat that would tack easily and quickly. These goals were acheived. The underwater part of the ARC 17 hull is a deep Vee hull shape forward which transitions into a round bottom shape at the transom. The deep Vee forward acts like a low aspect ratio daggerboard and provides 50% of the sideways lift force while sailing to windward. The other 50% of the sideways lift force comes from an oversized high aspect ratio rudder. The result is a much higher effective underwater aspect ratio lifting body and less induced drag due to generating side force than the full length assymetrical hull shapes. The other benefit of this hull design concept is that since the hull shape near the transom is round, it can slide across the water sideways with ease. When the rudder exerts a sideways force on the transom, the hull spins right around. On a beach cat hull shape that carries the hard corner and assymetrical hull shape right into the transom, when the rudder exerts a side force to turn the boat, the rudder and hull near the transom get in a fight. The rudder is pushing the aft end of the hull sideways and the hull is saying, "no, I am designed not to go sideways" and there is a large hull drag increase and the boat comes to a stop about half way through the tack. Now the jib must be backed to complete the tack and the boat backs up and this causes the rudders to have to be reversed as the boat backs up and finishes the turn. Now with no forward speed coming out of the tack, if the mainsheet hasn't been let out, the rudders stall and the boat goes into irons. What a complicated mess it is when tacking can be so simple with proper design.
Relative to the spinnaker:
With the effective sideways lifting part of the hull being in the front half of the hull, the ARC 17 handles a spinnaker very nicely, no lee helm. The 17 was my very first "shared lift hull design". The ARC 17 is the only boardless beach cat that will carry a spinnaker without lee helm for the above reasons.
Good Sailing,
Bill