All valid comments and thank you for your inputs.
How is it humanly possible to manually steer a boat for 15 or 20 days if you're on your own and for exemple having to deal with a complete electrical failure ?
I'd like a fail operational system but I know this isn't an airliner and event they sometime fail despite all what is done to achieve redundancy.
However I'd like to do my best not being on my own in the middle of the Pacific Ocean having to manually steer the boat ....
So here we are :
1/ How can we have a backup automatic steering in case of total electrical failure ? I was of course thinking of a wind vane system but I've heard this is not achievable on a SM/SN is that true ?
2/ How can you reasonnably deal with the said situation if you don't have such a backup ? Can you still setup a bungee system which would "steer the boat" while your'e having the little sleep you need not to kill yourself ?