Here's how our little band plays it:

The Dia(Am)mond is a ship(G), my lads, for the Da(Am)vis Strait she's bound(G)
And the quay(Am) it is all gar(G)nished with bon(F)nie las(E)sies round(Am)
Captain Thomp(Am)son gives the or(G)der to sail(Am) the ocean wide(G)
Where the sun(Am) it never sets(G), my lads, nor dark(F)ness dims(E) the sky(Am)
So it's cheer(Am) up(G), my lads(Am), let your hearts(Am) nev(G)er fail(Am)
While the bon(Am)nie ship The Dia(Am)mond goes a-fish(Am)ing for the whale(D)

Yes, that's right, "D" at the end of the chorus. We hold it for 8 beats (same number of beats as that Am-G-Am-G bit in the first line of the verse). Then we do an instrumental befor the next verse, using the following chords (I'm writing it out with one chord per beat here):

Am, Am, G, G, F, F, E, E
Am, Am, G, G, F, E, Am, Am