Captain Ahab
Captain Ahab is a one-way trail that forks off the Amasa Back trail. This singletrack requires expert-level technical skills, confidence, and strength. This is one of the more difficult trails in the Moab area. The singletrack is 4.3 miles in length. While it's one-way, it's not a "downhill" trail. From the ridgeline 2.7 miles up Amasa Back it will ascend 300 feet in altitude, but up-and-down riding tallies almost 1000 vertical feet of climbing over the course of the trail.
Riding notes, EPIC figure-eight:
0.0   Exit parking, uphill on road N38 31.710 W109 35.705
0.6   Drop R off road on Amasa Back
        N38 31.435 W109 36.096
0.7   Take air off ledge, turn right on DT
        Alt = ST straight shortcut
0.8   Cross creek N38 31.589 W109 36.080
1.0   Turn R (L = exit from Captain Ahab)
        N38 31.521 W109 36.261
2.3   R at fork (L = mid-way Ahab connector)
        N38 31.057 W109 36.804
2.7   R on DT (L = Captain Ahab)
        N38 31.098 W109 37.114
2.8   L (straight), R = to view
        N38 31.161 W109 37.126
3.0   Cliffside along Jackson Not-Hole
3.7   Pass Portage connector, keep straight (R)
        N38 31.721 W109 37.678
        (L=cliff scramble down into Jackson Hole)
3.8   Keep L at fork (R = Jackson ST)
        N38 31.761 W109 37.756
4.3   Straight (or R = jeep route)
        N38 31.788 W109 38.198
4.5   Keep L on Amasa  (L = Pothole Arch trail)
        N38 31.876 W109 38.369
5.0   View - End of Amasa - head back
        N38 31.619 W109 38.554
5.5   L on Pothole Arch
        N38 31.876 W109 38.369

6.6   Keep L (straight) to Pothole Arch
        N38 32.533 W109 38.449
7.4   At Pothole Arch - head back
        N38 33.106 W109 38.448
8.2   L on Rockstacker
        N38 32.533 W109 38.449
9.9   L uphill on DT, cross ridge
        (R = Jackson ST)
        N38 31.747 W109 37.594
10.2 L on Amasa
        N38 31.761 W109 37.756
11.3 R onto Captain Ahab
        N38 31.096 W109 37.113
13.5 Cross midway connector
        N38 30.812 W109 36.597
15.6 Join Amasa, downhill

        N38 31.521 W109 36.261

15.8 Cross creek
16.0 L down Kane Creek Rd
16.6 Back at parking
Getting there: Head south on Moab's Main Street. When you reach the McDonald's on your right, turn right onto Kane Creek Blvd. After 0.6 miles, go straight where the road seems to turn right (500 West). Drive along the Colorado River about 5 miles until the road turns to gravel, and head uphill about 2/3 mile. Watch for the "Amasa Back Parking" area at GPS N 38 31.329' W 109 35.501'. Park here. Pedal further up the gravel road 1/2 mile, and turn right onto the trail at the sign.