Sea
The sea, as opposed to the ocean, has known boundaries, and thus can be interpreted as being symbolic of the "known quantities of life." Inasmuch as the sea can symbolize life, a journey across the sea can be seen as a symbolic journey across the "sea of life." Information taken from: Online Symbolism Dictionary
Water: Water popularly represents life. It can be associated with birth, fertility, and refreshment. In a Christian context, water has many correlations. Christ walked on water, and transmuted it into wine, thus these acts can be seen as a transcendence of the earthly condition. Christians are baptized with or in water, symbolizing a purification of the soul, and an admission into the faith. However, water can also be destructive (as in the biblical flood which only Noah and his family escaped); water drowns and erodes, wearing away even the densest of stones given enough time. Water is also one of the four elements essential to life in traditional western philosophy. In this form it is represented by undulating lines, or a triangle pointing down. Colors commonly associated with it are blue and green. Its qualities are fluidity and cohesiveness. Flowing water usually represents change and the passage of time. Information taken from: Online Symbolism Dictionary
Songs referenced:
Flying Dutchman