Drunken Sailor is Dorian.

Mr. Red. You asked about a guide to modes etc.

Get hold of " The Lydian Chromatic Theory of Tonal Organisation in Improvisation and Arrangement" by George Russell. This is the book which triggered the use of modes in Jazz in the 1950's. Russell is a drummer and though the book is verbose and complex, its ideas are completely relavent to folk music - or any other kind of music for that matter.

I had the whole system hammered into me at college and it has revolutionised my musical thinking evere since.

The George Russell book is expensive (around £50!!) But this is cheap for the benefit you will get out of it. Alternatively, get one of Jamie Aebersold's superb jazz playalong albums. The scale syllabus encompasses modes, altered modes will sort you out and it suits all standards of musician.