I have made the rudder as per the drawing, using a piece of solid oak dowel (25mm od) for the rudder post. A local carpenter kindly cut 6mm slots in both ends of the dowel for the 6mm rudder blade to fit in (I plan on making a spare spare LOL). For free! See it pays to get out of big cities!
The clearance inside the scupper was not much, so I took a piece of fibreglass painter pole, and cut a 3mm vertical slot in it. This is now a nice firm push fit down the scupper as it compresses, and ensures that constant use of the emergency rudder will not disastrously wear through the scupper walls. I cut a piece of 12mm marine ply to fit over the compressed glass tube, leaving some tube above to support the rudder (which will probably have neutral bouyancy anyway, being all wood).
Next I cut another collar from the ply, with a hole to be a snug fit on the rudder post itself, and drilled a hole through both for a carbon rod I had lying around (might replace this with a thin SS bolt and wing-nut)
I am also adding a small ring on the top of the post, so a line can be dropped through the scupper, gathered up from outside, and then clipped on to the post, to pull it up through the scupper.
So now I have a rudder which will fit either an AI or a TI, and all I need to do now is add a tiller (more oak dowel, with a 6mm SS threaded rod inserted in the end, with a wing-nut to go on the back of the rudder post. Plus of course cover all my mistakes in safety orange paint!
The only limitation I envisage is that with the emergency rudder fitted, minimum water depth needs to be a bit over 2 feet, so removal of the rudder after the emergency will require some wading, a small price to pay for saving your bacon, IMO
The real beauty of this rudder is that a bunch of us could be out on an offshore excursion, and the emergency rudder could be handed over to whoever needs it. I know the chances of the steering becoming totally unservicable are very slim, but having been retrieved after drifting about 7 miles out to sea after a rudder line broke internally, and having broken two rudder pins on the one offshore outing to Broughton Island, I do not wish to get caught out again.
I can actually see it being good practice for every group venturing offshore to have one of these available within the fleet.
Photos will magically appear soon LOL