How did hamlet get off the ship to england?

The incident in which Hamlet gets off the ship to England plays an important role in changing the entire plot. As he was being "escorted" to England by Guildenstern and Rosencrantz, he switches the letter that the King had given with the one he writes. The original message that the King had wanted to pass on contained an order to kill Hamlet in England. However, Hamlet switches the letter with a new one which orders for Rosencrantz and Guildenstern to be executed.
After this, a pirate ship attacks the ship that Hamlet was on. We are not given much detail on such an occurrence but we find out that Hamlet got onto the pirate's ship as the pirates were attacking the ship that was supposed to take Hamlet to England.
Shakespeare does this in order to bring Hamlet back to Denmark and resume the plot. Although, the literary merit behind such a plot manipulation is widely debated as being either acceptable or flagrantly unacceptable.