Oft I Must Strive

Riddle: oft i must strive with wind and rain, battle them both when under the sea. I feel out the bottom, a foreign land. In lying still I am strong in the strife;if I fail in that, they are stronger then I, and wrenching me loose, soon put me to rout. they wish to capture what i must keep. I can master them both if my grip holds out, if the rocks bring succor and lend support, strenght in the struggle. ask me my name!