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                                   E  Am
Fifteen men on the dead man's chest

Am                                         E  Am
Drink and the devil had done for the rest.

Dm                             Am
The mate was fixed with the bosun's pike

         Dm                      Am
and the bosun brained with a marlin-spike.

    E
Cookie's throat was marked belike


Ref:

Am
It had been clutched by fingers ten.

E
And there they lay, all good dead men,

Am
Like break o' day in a boozing den

E                        Am
Yo-ho-ho 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.