You have to time the guards, and sneak past them (they can see through sneak and invis) to get to Doran. Here is the route we took:
Route Map (click to enlarge)
TIP: A developer has stated that "each time a guard catches you, his detection range shortens slightly". This may still take a lot of trial and error.
TIP: Use the 3rd person camera and your knowledge of line of sight to your advantage and try to plot a good route to take as well as watch all the guards' pathing routes. Once you're in a "safe" location don't be afraid to sit there for a while watching pathing.
As you reach the end of the entrance path there will be two guards on your left as well as one that paths onto the stairs that are to your west. Watch their pathing and which direction they are facing. Once they are facing away or aren't nearby...
Head west to 27, -4, 9 - wait by by escapee; when guard above heads the opposite way down, jump on the crate, to the stairs, then run up the stairs and west to..
44, 0, 11 - wait behind the barrel for the pathing guard to head back to the staircase you just came up, when clear head for the north stairs. Go north, slowly tailing one of the guards patrolling the fountain (but being far enough ahead of the other) to...
39, -4, -46 - in corner by prisoners. Next, watching the fountain guards pathing, head west to..
52, -4, -46 - small spot by a skeleton, if you're fast enough (or wait for another opening) next move further west to..
76, -4, -34 - this is an inset near a doorway. From here watch not only the pathing guards but also a guard on a small staircase to the south. The southern guard won't move much but you need to be sure he isn't facing your way. When timing is right, run south, jump on the first barrel you see then quickly onto a crate (but not to the topmost crate!), which puts you at..
68, -1, -16 - here you should be on a lower crate next to a ledge. The guard up here can be almost be right next to you but should not see you here (line of sight). When that guard begins to move away toward a southern staircase further in, very quickly jump straight from your crate to...
72, 1, -16 - don't hesitate (the guard will quickly return), go west across this landing and then drop down the southern ledge to...
86, -4, 3 - your target is straight south of you now, inside a cell. There's two guards that walk toward and away from each other. Even at their furthest distance apart, this step make take a few tries due to their huge awareness range. When they start moving apart make a run for the cell door, open it and rush inside.
It's possible to get the update for reaching Doran before speaking to him (if the guards catch you while entering into the cell) so you'll have to run the entire gauntlet again if you don't get far enough in to speak to him.
Doran is located at 90, -4, 30 . Speak to him.
NOTE: As of January 30, 2012 Doran will not follow pet classes unless they dismiss their pet first. 'However' once Doran is following you you can call the pet back.
Once Doran is following you, you no longer need to be stealthy. Head for the fountain and fight any guards that attack you.
Captain Xalkastiz can be found at 58, -4, -38 . He will turn into a standard mob two levels above you.
Once he is subdued get Doran out of Scale Yard; fight off any more guards that attack.
The quest will auto-complete when you reach the gates to leave Scale Yard.
Doran reminds you to return to Kain in East Freeport.
If you are still having problems with the pathing see the video below.
Kain Starkson needs the expert navigational skills of his old crewmate, Doran the Crow. Unfortunately, Doran's been imprisoned in the newly established Scale Yard, and I need to break him out without making a scene. This is going to require craft rather than brawn.
I must enter the Scale Yard prison and find Doran the Crow without being detected.
Enter Scale Yard: Scalebreak!
I've snuck into the Scale Yard.
I've entered the Scale Yard.
Now comes the hard part. I must find Doran the Crow without being detected. The guards' helmets should dampen sound sufficiently to let me sneak around, so long as I stay behind them.
Reach Doran without being caught
I've reached Doran without being caught.
Speak to Doran
I've spoken to Doran.
I made it to Doran without being detected.
Doran can administer an amnesia elixir to the guards, so stealth is no longer required. However, I do need the gate key, held by Captain Xalkastiz in the tavern near the fountain.
Subdue Captain Xalkastiz
I've subdued the Captain and taken his keys.
I've relieved Captain Xalkastiz of his key.
I must avoid or subdue guards and help Doran escape through the main gate.
Help Doran Escape
I've escaped the Scale Yard with Doran. I should inform Kain of my success.
I've freed Doran from the Scale Yard, completing Kain Starkson's ship crew. Perhaps now that he has everyone assembled, he'll be ready to sail... unless he's still slowly drinking himself to death near the tavern on the docks.