The Tanaga Pass is a strait between Tanaga Island and the Delarof Islands the Aleutian Islands of Alaska. It is about 40 miles long and 13 miles wide at its narrowest part. Tidal currents commonly range between 2 and 3 knots in the pass.
Map of Tanaga Pass, United States
From the U.S. Coast Pilot: "Depths of 50 fathoms or more can be carried through the pass by keeping 6 miles off Cape Amagalik, Tanaga Island, and 3 miles off the Delarof Islands.
"The direction and velocity of the current is radically affected by the land areas and the banks. It appears that the flood is diverted by the chain of islands – Skagul to Unalga – and the relatively shoal water between them to an E and W direction in moving around this chain. It was observed that S of Skagul Island the flood sets about NE, E of this island it sets N, and N of the island it sets N to NW.
"With erratic currents of this nature, dead reckoning cannot be depended on and the navigator may find his vessel 1 mile or more off his reckoning after a run of 1 hour. During observations made 4.5 miles SW of Cape Amagalik, the current was rotary, turning clockwise, and followed a definite pattern. A minimum current averaging about 0.8 knot sets N to NE."