If you wanna play the song easily like I wanted to you only need 3 chords.

listen to the song to know when to change chords and how the rythm is going.

Intro:

Am Em Am x2

Verse:

Am (x02210@1)                                 E (022100@1)AmFifteen (x02210@1)men on the dead man's chest

Am (x02210@1)                                       E (022100@1)AmDrink (x02210@1)and the devil had done for the rest.

Dm (xx0231@1)                           AmThe (x02210@1)mate was fixed with the bosun's pike

Dm (xx0231@1)                    Amand (x02210@1)the bosun brained with a marlin-spike.

ECookie's (022100@1)throat was marked belike

Ref:

AmIt (x02210@1)had been clutched by fingers ten.

EAnd (022100@1)there they lay, all good dead men,

AmLike (x02210@1)break o' day in a boozing den

E (022100@1)                      AmYo-ho-ho (x02210@1)and a bottle of rum!

Intro-thingy again

That's all you need for the song! The rest of it is just the same. Atleast now it should 
easier for you to listen to the song and put in the right chords.