This book is Excellent
It is however written for traditional rigs in mind. I doubt that Don was thinking of Hunters only when he wrote. But, he was for sure not writing it for furling systems, since he references the battens and adjustments for trim that can not be done with furling systems. However, if you read it carefully and apply what you can to a furling system, it will have you light years ahead of where you may presently be with regard to your sail trim knowledge. I use the book all the time, have read it at least a half dozen times and gain something new with each additional reading. Just learing about draft and depth of it and how to interpret what the tell-tales are indicating will have you sailing much more efficiently in no time at all.It is well worth the stipend that is charged. It is always in the cockpit with my charts when I am at the wheel.