Time to put that Sandskif to work. Head west to the catch-a-ride and spawn one of the sand ships. Hop in and get moving. Simply aim the bow directly towards the next waypoint, to the north-east, and you'll find the Wurmwater Passage in no time.
To find Captain Scarlett's ship simply zoom forward, through the tight passage, then swing a right. You'll spot the orange glow of her tall ship in a covered area. Make sure you stay in your skif, mind, as you'll have to deal with enemy transports upon arrival.
Simply use your skif's guns, making full use of its ability turn and fire in a strafe (it's a hoverboat afterall, not a car), and take out the raiders that attack. With all of them dead, Scarlett will radio you. Head tot he read of her ship and climb up, using the elevator once on deck to reach the top of the ship and finally talk to the titular Scarlett. Easy