I'd put the order of priorities of pirates this way:
-Survive
-Earn as much money as possible
-Kill as many pirates as possible
So, in the case that pirates are perfectly trustworthy, a follow-up to Titandrake's post:
[EDIT: actually, it doesn't work; I'm still thinking on it, but I forgot that in a 4 crew ship, any deal that doesn't involve the captain requires all other pirates to agree, so that they represent the majority]
-With 4 pirates, if no promise is made, the second pirate will accept whatever the captain offers, 0 coins included, or otherwise he will die, as Titandrake said.
However, the third pirate can strike a pact with the second pirate: if he votes against the captain, he will accept a 0, 100, 0 split afterwards, which the second pirate and fourth pirate would normally accept, since that way they kill one extra pirate; but the fourth pirate can also offer a 0,0,100 split, which is equivalent for the second captain; as such, they will both rise their offers until they both reach 99 coins for the second pirate and one coin for the relevant pirate, so that doesn't seem like a very good split for the third or fourth pirates. Assuming (*), this means a 99, 1, 0 split.
Thus, the captain (a bit nervous since everybody is discussing his death) will instead try to earn the loyalty of the third or fourth pirate, and one coin for the fourth pirate should suffice , since otherwise he would earn nothing. But! Whatever 100-n, 0, 0 n split the captain proposes, the second pirate can offer the same to either the third or fourth pirate, and they will accept, since they are bloodthirsty. As such, the captain, trying to survive, will offer the 100 coins to either the third or fourth pirate, and the second pirate, seeing that he will earn nothing, will also offer 100 coins to either the third or fourth pirate, as he is bloodthirsty.
Probably before reaching that point, the captain and the second in command will realize that it may be better to reach an agreement between them, but that's prisoner dilemma: if the captain offers a 100-n, n, 0, 0 split, the second pirate could accept, or try to get a better deal with either the third or fourth pirate, which is always possible, since a 0, n, 0, 100-n split seems better for him (he gets to kill the captain); but that reasoning leads to a 0, 0, 0, 100 split (according to the previous paragraph), which is worse than the previous 100-n, n, 0, 0 split...
Adding extra rules about how and when the pirates can strike a deal would make this quite easier... or solvable...
*I would add that, if a pirate has the choice among more than one deal that are equivalent to him (according to the three laws of buccaneering above), he will choose the one proposed by the highest ranking pirate. It can shave some lines of discussion for higher number of pirates.