In my original post on the sail drone, I expressed some pessimism that the thing would work. In the meantime, the saildrone people put up some more information about their project and their designers. Seems like they have enough experience to make the sail drone work. One of the interesting things about the ocean is that the bigger the thing floating on it is, the more vulnerable it is to the forces of storms. Small things like plastic bottles or coconuts can cross oceans with impunity. So as long as a drone is small enough, it is probably impervious to damage.
Still some problems remain for any autonomous drone. The main one would seem to be collisions with ships and land masses. Autonomy is one thing, avoiding collisions is another and adds complexity to the design. The other problem with anything floating on water and containing electronic gear is water proofing. As anyone who has ever bough a waterproof anything knows, waterproof is an optimistic term. Water seems to be able to outwit almost any sealing technology so far invented. Perhaps the most reliable technology is still the cork. But we will see. I am keeping my eye on the sail drone website.