Physically the M18 is a wider A-class with a spinnaker. From what I am told, the width makes a big difference in stability and speed. Keep in mind this is pretty much a custom boat. I know from talking to Goran Marstrom that they can build this as a 1 person or a 2 person or a 1 person sometimes 2 person boat. This is done by changing mast stiffness and sail cut. You can also convert a A-Class to a M-18 with a kit. For what else they can do, you need to talk to Marstrom.