A working hapa model has finally been accomplished by Frenchman Luc Armant. It is the realization of the theoretically perfect sailboat: an airfoil and hydrofoil, tied together by a single line in tension. The massless sailboat has long been the dream of sailing pioneers from Bernard Smith’s aerohydrofoil to D. Costes’ chien de mer (seadog) to the hapas of J. Hagedoorn. The achievement cannot really be overstated, IMHO. Well done, Mr. Armant! The device is described in this (massive) PDF file. I look forward to the English translation.