voluntary v. involuntary choices

Aristotle argues a lot about choice; he claims that choice is either voluntary or involuntary but that each has it's own conditions. But as much as Aristotle talks about virtues and choices and happiness and good, and tries to explain how each is so distinctly definable, so many of his arguments are laden with so many conditions that it's hard to understand just how distinct each one actually is.

His greatest example of this comes on page 119 where he talks about a sailor who has to throw things off a ship not because he wants to, "but to save his own life and that of his shipmates [as] any sane man would do." He claims that this is a "mixed" act because it was not a task he was willing to do but voluntarily did so. But, he later argues, it is a voluntary act because he did it without being forced to do so.

 Then, comes the argument on page 123 that argues the difference between an act done through ignorance versus in ignorance and how they are either voluntary or involuntary. Here, his logic becomes almost cloudy (at least, personally); he claims so many different things here that it's hard to keep track of what he thinks is right and what he believes is wrong. He talks about how "an act done through ignorance is in every case not voluntary, but it is involuntary only when it causes the agent pain and regret." What is the difference between "not voluntary" and "involuntary" here?

It seems as though Aristotle has so many conditions and ideas on choice that he has almost every situation covered; but when he says "choice is manifestly a voluntary act," how can he argue certain acts are involuntary? Aren't all acts voluntary because we have chosen to do them? If we really didn't want to, wouldn't we just choose not to do them? If we're acting through ignorance, shouldn't the act still count as voluntary because the actor had not chosen to inform himself of the consequences beforehand?