I'm not convinced that your comparisons are ultimately the best option for what you're trying to describe, but I'll use them in my explanation nonetheless. (Galastel's answer better addresses the content of a metaphor.)
A metaphor still needs to name the thing you are actually talking about. Context can help, but saying the thing outright is best. If the reader has to sit and thing "what is the noose?", you've taken them out of the story, rather than immersing them in rich visuals as you intend. If you have doubts, trying turning what you are saying into a simile first. Adding "like" or "as" makes it much more clear because you are forced to say what the actual thing is you are talking about.
The snake slithered around my body as a noose slithers around a neck.
The waves cut into the ship like blades and it sank.
Then work your simile into a metaphor. A metaphor is simply more directly saying that the snake is a noose and the waves are blades. Now that you've seen the simile version:
The snake was a noose around my body.
The waves were blades, cutting into the sinking ship.