Okay finally finished!
And to butt in on your conversation, I've actually heard Coach used before in real life, so I wouldn't worry about getting it from any certain book or anything.

This simile is kind of funny, and I don’t think you meant for any kind of humor here. Also, since she’s in the ocean there’s a chance this simile could be literal, making it funnier, so I really think you should change it.
Though I do like the mental image. xD

I’d add ‘only’ after ‘was’ so as to continue to minimize chances.

This sentence was kind of lost on me and, unless this happens later in the story when readers already know the character, will probably be lost on most readers. Does she think she’s worth a lot? Does she not? What does this entail? Since we don’t know the character, we can’t use this as a measurement for how hard she’s fighting.

‘god-knew’. Just a little tense issue.

Since you just used her name, I’d change Aimi to ‘She’.

I’d change ‘alas, kicking’ to ‘it’, since you just mentioned she was kicking.

I’d cut out ‘though’.

I’d change ‘take’ to ‘obscure’, since ‘take’ seems to imply they’d take it permanently, or at least do some kind of lasting damage.

I’d cut out the second ‘she’.

How can she tell?

I’d cut out ‘itself’.

I’d drop this into its own paragraph because it seems to open up a new train of thought.

‘It’s’ to ‘It was’. Just a little tense issue.

I really liked this whole section. These short sentences especially. There is a lot of power in them.

I think ‘swiveling’ only has one ‘l’.

How can she tell he’s young? I can understand knowing he’s male, what with the big hands and all. I have another little issue with this since you just told us she couldn’t feel anything, and I quite liked that part.

I’d cut out ‘a’ and ‘time’, but that’s just because I like short sentences, there isn’t anything wrong or confusing with how you have it now.

I’d cut this out if only because I don’t understand what shivering has to do with her inactivity. I thought it was a temperature change?

I’d cut this out because, well, if she just nearly drowned isn’t kind of obvious she’d be exhausted? I think this would make more sense once she’s waking up in the house. (Which you already have a line there that serves this purpose.)

I don’t really understand this sentence. The way this is phrased (because of the ‘Though’) it makes it sound like her eyes being closed should be keeping the darkness away. But because they’re closed, doesn’t that invite darkness by its very purpose? I’m not really sure where you were going with this, so I don’t have any suggestions, but I thought I’d mention my confusion about it.

I’d change ‘bad dreams’ to ‘nightmares’.

And here’s where I start talking without knowing what I’m talking about. Hooray!
I’ve never done much research on amnesia, so feel free to ignore this entirely. But her questions of who she is seem to stem from nowhere. She doesn’t recognize the place she’s in so she wonders where she is. She feels tired, though she’s been asleep, so she wonders why. But what brings on the question of who she is? I think this would make more sense later when she hears that her saviors don’t know who she is either.

I’d cut out ‘to a sitting position’, because the reader will automatically assume it.

I’d cut out ‘big’. Though I really like that you’ve kept up the theme of waves being the villain.

I’d cut out ‘in pain’, because you just mentioned it.

I’d cut out the first ‘and’ and ‘as well as’, then replace ‘as well as’ with ‘and’.
“… but all she could remember was the water, the strength of the current, and the darkness below.”

I’d change ‘whatever’ to ‘something’ or something like it. ‘whatever’ seems a little informal for the narrator to say.

Since you just mentioned that he turned slowly, I’d replace it with something else in this line. Maybe just ‘His shoulders were high and tense’?

Ellipses should be three dots/periods instead of just two.

‘shook’ instead of ‘shaking’. Just a little tense issue.

While she would be perfectly justified in panicking, she doesn’t really seem to be acting it. She’s acting more like she’s taking this very well or in shock.

I’d separate her thoughts from narration with either single quotes or italics. Anything to distinguish it from regular narration. I’d also add a comma after ‘boy’.

There seems to be an extra ‘back’ here.

I’d change one of these ‘before’s.

I’d say ‘around Isaac’s age’ since they are both older and younger.

This made me giggle. I like these two already. I don’t know if you intended it, but you seem to have gotten the ‘laid-back beach folk’ down really well. Of all stereotypes, that one seems (to me) to have the most truth to it.

I also think an extra period snuck its way in there.

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I like the characters already, which is a really good thing. One of the biggest problems I find in writing is that I don’t much care what happens to the characters. Without much interaction, you’ve already made them likeable.

I also really like the way you describe scenes. Sometimes sentences get a bit wordy and the reader can get a bit lost, but overall I liked them.

I hope my critique lived up to expectations! I wish you the best of luck.

About Chapter 2:
I’m not sure if you would like me to wait to critique until your done or just go at it now? Unless you don’t want me to, in which case feel free to say so. =]