It seems to me that there are many ways to tie to a bull rail as there are people who have ever tried to secure their vessel to one of these splinter infested dock structures.
In the Pacific Northwest they are a way of life. I've studied most every method I have seen and settled on one Capt. Bill Douglass showed me at Auke Bay, Alaska.
The technique was shown to him by an anonymous captain, so I have therefore christened it the "Douglass Hitch" after the Captain who taught it to me.