I've read this several times now and I'm hearing what it's about, I think. I't's a very aural poem - I hear the sounds of the 'snoring' waters and the 'trickling' and 'pelting' as the waves fall back into the sea from the rocks. You follow through a metaphor (the bed, restless sleepng) very well. I'm not sure what the tragedy is, though I can perhaps make a guess. As usual, you use words like musical notes, very effectively.