vega, thanks for the explanation on the amsteel rigging. I'm going to consider implementing this as another back-up to my existing method which is bringing along some of my old rigging I replaced. My old rigging is one size smaller and has the original fittings but I think it will do in a pinch, and I already own it.
I can't find any info on the Bristol 27 so have no idea of the hull design but the reality is that most sailing vessels will self steer with the right sail trim, indeed I have less trouble with Raven (fin keel, spade rudder, no skeg) and our PB (28' full keel cutaway forefoot). It is of course possible that the reason for that is experience.
I'd urge you to have a loook at Alex's (Giulietta) sailing videos. One of them covers steering without a rudder and if that speed machine can be made to self steer then anything can do it.
tdw, here are my hull lines (you'll have to scroll down the page to them):
My experience with sheet to tiller arrangements has been, for the most part, successful. The problem I have encountered the most is inconsistent winds. This makes it difficult for me to relay the information from the sails to the tiller without having to change the arrangement of block and tackle and tension of the shock cord. With consistent winds I have much better success.
Of course, experience is huge and mine has been limited. I'm hoping to get much better at balancing the boat and arranging self-steering systems next season, even with my new windvane available. My boat seems pretty sensitive to conditions so I'm expecting this to be a long learning curve. John Letcher's book explains the forces at work pretty well so, like you said, more experience is key.
From the accounts of voyagers I've read windvanes can break so having a back-up steering plan is necessary when I go for my first passage. I'll check out alex's videos on sailing without a rudder, too.