Once you let go of the charge attack, you'll move forward automatically, and upon entering the water, the speed of the dash will carry over for several moments - letting you get to and from your ship quickly.
To perform this correctly, you will either need to stand on a ledge (this can work either on a rock or cliff facing the ocean, or on the edge of your ship), or you can stand in the shallows just one step before you enter the water to swim.
