Actually "Wanker" is an old fisherman's term for the leading hand among those persons whose task it is to refurbish the hooks on the long lines--the master baiter--
This downwind idea may apply to any vessel requiring additional rudders when sailing downwind--it is an old ploy seldom seen these days. The transom needs to be solidly built or it can be reinforced with an additional heavy crossmember, and to the transom just above the waterline are fitted wooden brackets (or stainless steel) which protrude about ten inches from the vessel. The inside sides of the brackets can also serve double duty as a step support.
Into these are slotted wooden dowells at the extremities, so we now have a slot down which is slid a long narrow laminated fixed rudder
of fairly high aspect ratio, designed to drop until it sits on top of the bracket and rest against the dowel. The top of the board rests against a rub-strip fastened to the top of the transom and the board is retained by a lanyard.
If the board is forgotten about and grounds or strikes something solid the dowel shears and the board comes out of the slot, and is trailed astern by the lanyard until a new dowel is fitted. Two can be used, but it is possible to fit more of them on a larger vessel if required. They do not interfere with the normal rudder as they are generally mounted well clear of it on full turn unless the rudder is also mounted on the transom.