I have finalised my steering system ideas, at least the stern end of the system. I have long wanted 2 things in almost all of the systems on the boat, redundancy, that is, if one breaks there is a back up system that immediately kicks in, 2 masts but the boat can sail on one, 2 motors but the boat can cruise on 1, and with the steering system I want hydraulic steering but I also want a mechanical back up that can easily be employed in the event of the hydraulics failing.
My solution is to have a tie rod connecting the 2 rudders and to have the tie rod driven by the hydraulic ram and to have an emergency tiller attached to the tie rod. The huge advantage of having the emergency tiller attach to the tie rod is that I can hand steer from inside the cockpit rather than the usual point for an emergency tiller, directly over one of the rudder stocks on the rear steps. If I need to hand steer for hours or even days, I don’t want to be stuck out in the elements on the rear steps where visibility is poor. From where my emergency tiller will attach I will still be at my helm, where I can still read all of my electronics and stay out of the elements. And of course you are steering both rudders with the tiller.
Also attached to the tie rod will be the autopilot ram. If either of rudders should jam then the linkages can be disconnected so that the other rudder is freed and the boat can steer from one rudder until the other rudder is freed or fixed. I believe that the hydraulics of driving a tie rod is much simpler than driving 2 separate rudders in unison so that should both simplify the hydraulic system and be cheaper to install. I am not sure of whether this is also true of the autopilot system hydraulics, but I would imagine so.
One final advantage of the tie rod is that the conduit glassed in with uni stiffens up the duckboard. Not that that is going to be an issue, once the hatch walls go in, and the back wall glassed on, the box section will create a massive girder across the stern, stiffening it all up. I did want the duckboard stiffened considerably as I plan to use the large centre hatch as a bath so it will need to be able to easily support around 500kgs. I will glass a second conduit in which will be used for wiring to cross the rear of the boat, in particular the outboard umbilicals.
The tie rod I settled on is a 30mm aluminium tube inside a 31mm inside dimension plastic conduit. I needed to have the tie rod inside the conduit before I could glass it in because of the length. I could get it in and out during construction in an emergency if needed but that would require cutting a hole on the side of the hull and of course I wanted to avoid that. Besides having the tie rod inside the conduit, even though I am levelling the duckboard before glassing the conduit on, I can ensure the rod is still sliding inside the conduit once it is glassed on and then just let is set overnight. My fear was that if I glassed the conduit in without the tie rod inside and got even a slightly curved conduit (in any direction, up/down or fore/aft) then the tie rod would no longer slide easily inside the conduit.
The pics below show the space the outboard takes up in its well, so in the lowered position there is only room for a 200mm tiller arm on the rudder stock. So I mocked up a steering system out of timber pieces to ensure a tie rod on the duckboard could be connected to the tiller arms around the engine bay and work the rudders correctly. They worked perfectly. The ends of the tie rods will be connected to steel arms that are shaped around the engine bay to connect to a turn buckle that will connect to the tiller arms. The reason for the turnbuckles is so that there is toe in adjustment on the rudders. All very simple.
Once I had the peel ply removed and the conduit position marked on the duckboard I mixed up a sloppy mix of coving material and poured it between the 2 marks (front and back) I had in order for the conduit to be bedded in it. I then mixed thicker coving material and make the coves each side of the round conduit in order to glass over from one side to the other. I then wet out 2 lengths of 450g unit and laid them over the conduit overlapping across the top so that it has 2 layers over it. The I wet out a 250mm wide double bias layer to span from one side to the other with at least 50mm on each side, then a final 200mm double bias layer again spanning from one side to the other. To finish it all off I applied peel ply.
Tomorrow I will continue with the construction of the rear steps each side (off the boat) and perhaps start gluing and glassing the framework for the raised duckboard. I also have to start glassing the davits on the outside.