He is talking about the Folkboat – (the Folksong is a Folkboat derivative):
“She (the Folkboat) has considerable aft rake to her rudder, which results in less lateral plane and less wetted surface. There was a time when some sailors thought this feature was detrimental to self-steering, but this thinking is not so much in evidence today.
. . . a considerable rake aft often causes the rudder to operate more efficiently when the boat is heeled or rolling, at which time the resultant of force components working on the rudder is acting in a more lateral and thus more effective direction. It is also true that gravity tends to keep such a rudder amidships when the boat is unheeled*. The really important concern with regard to self-steering is the directional stability of the hull, which is generally achieved through a reasonably symmetrical shape with somewhat balanced ends and an ample, but not necessarily extreme, length of keel.”
* And presumably the heavier rudder will be more effective in maintaining this.
On Blue Mistress, I am able to leave the tiller and go forward to adjust lines at the mast – (usually to loosen the lazy jacks which interfere with the mainsail shape if left too tight). She holds her course for the time it takes.