This song was written by Paul Simon about his wife ... The sail on silver girl bit refers to the time Paul's wife was upset over the fact that white hairs were beginning to appear on her head. So let not your heart be troubled and enjoy the cache!
Bridge Over Troubled Water Lyrics
When you're weary, feeling small
When tears are in your eyes, I will dry them all (all)
I'm on your side, oh, when times get tough
And friends just can't be found
Like a bridge over troubled water
I will lay me down
Like a bridge over troubled water..