For anyone who's interested, I've cobbled together some scruffy sketches and instructions for making twin rudders stern hung as a modification for Drascombe Luggers and Longboat variants, the drawings are NOT TO SCALE and no measurements are given,(the transom is at 37 degrees) however, it should not be too difficult for anyone to determine the size and position of the rudders by making hardboard patterns before proceeding with the build. Do make certain to allow for unobstructed movement and sufficient clearance for stern to beaching without grounding the blades.
To build the rudders, begin by making hardboard or similar material patterns, when satisfied with them, use 9 mm marine ply for economy of materials as well as keeping the weight down, (unless you already have some other suitable material to hand).
Cut all the parts following the final pattern shapes, then clean up and dry assemble the rudders, do the blades separately. When dry assembled, drill some 1/4" holes at various positions right through the wood sandwich, these holes will make accurate assembly easy when everything is glued and cramped together because wet glue makes everything very slippery. 1/4" hardwood dowels driven through the holes ensure everything lines up perfectly, the dowels will be left glued in place.
Dismantle all the pieces, abrade the surfaces to be glued with 60 grit or 80 grit abrasive paper, this improves penetration of the adhesive and provides an additional mechanical key. Phenolic resin or Epoxy adhesives are suitable.
Liberally apply adhesive to all surfaces as required, lay the first piece on a flat surface then create a wood sandwich of all the parts, using the 1/4" hardwood dowels to accurately locate them. Use a pencil sharpener to put a bit of a point on one end of the dowels to help with the line up of the holes when driving the dowels through the sandwich. When fully assembled, cramp all together ensuring firm pressure is applied to get good joint adhesion. If using wooden pads to prevent cramp marks, place a piece of polythene under the pad to prevent it sticking to the rudder if any glue squeezes out, which it should do!
When the adhesive is fully cured, all that is required is a general clean up, then fit everything together with the blade to make certain that all works as intended. Profiling the cross section of the blade will reduce drag and weight, but don't profile the section between the rudder cheeks, that must be kept parallel. (The blades may need to be reduced in size after sea trials if found to be too big) Decide where to locate the pintles on the rudder, and of course the best position on the transom at the same time. (The length of the metal arm on top of the rudder will restrict how far outboard it can be from the centreline of the transom) A strong shock cord will keep the blade in the down position, a lifting line will keep it raised when needed. A metal arm on top of the rudder stock will take the steering lines, the the top of the rudder will need to be angled to minimise the rise of the metal arm when the rudder is turned, adjust this angle by trimming off any excess when the rudder is hung on the transom. When all has been fitted in place and approved as suitable to work correctly, remove all of the pintles etc. and prepare the rudder for painting of varnishing depending on your personal preference. The fitting will be reinstated afterwards.
The steering lines pass through dead-eye leads in the transom, close to the port and starboard side of the hull and just above deck level. Further dead-eye fair-leads will be fitted to the deck as shown in the drawings.
The fittings to take the steering lines and tiller are as follows: A replacement for the top rudder guide needs to be manufactured from Stainless steel, Bronze, Brass or Galvanized steel (your choice) A tube about 12" long will be welded to the underside of the guide to take a spigot replacement for the original rudder shaft, the spigot must be the same diameter as the original shaft because it has to accept the original lifting tiller/rudder head fitting. You could modify your existing top guide if you are prepared to do that. The metal arms on top of the rudders must be the same length as the arm fitted to the spigot under the tiller fitting, centre to centre, to ensure equal movement of the steering lines. The metal arm is secured to the spigot by the collar and a grub bolt which locates in a dimple on the spigot, similar to the existing grub bolt that is on the tiller/rudder head fitting on the original, the tiller fitting will also need a dimple in the spigot to locate above the collar on the metal arm.
As this is completely untried at present, there will probably be some minor teething problems encountered during the construction and actual working operation of the set up. A possible problem that could occur is the tension of the steering lines not being constant when the rudders are turned, (because of the arc described by the metal arm) a likely simple solution would be to incorporate a couple of short lengths of strong shock cord in the steering lines to allow for this.
If anyone does decide to give this a go, please make sure you take plenty of photographs which may be helpful to others who wish to make the modification.