I believe that ad means a rudder
in front of the boat and one in the back. The one we can see is tiny, so I believe that supports there being one in the front. I haven't found anything on the web other than larger Dynaflyers, and they are canting keels.
I'm going to guess this boat is a prototype where they were experimenting with a forward rudder
. I think it was Blackaller that did one in the America's Cup. It was sometimes fast but mostly they worked hard to make it work
When you look at it, if it has a forward rudder run away. Even if it doesn't the rudder you can see is too small. You need a tried and true design good for learning
on, not an experimental boat that you won't have any idea how to figure out even if it is possible to sail it well. It could have been a complete failure.