About a person who flaunted morals and conventional wisdom ("I have no need of a chart or creed"), betrayed or used everyone close to him/her ("those landsmen who you but lately knew/Were left stranded on the lea") and lived life heedless of the consequences ("the flag you flew was a pirate cross"). The narrator tried to convince this person to change his/her ways, but gave up in frustration ("you paid no mind to the warning signs") and is now watching from a distance as the consequences of his/her actions catch up with him/her: "Don't call my name when your ship goes down"
About a person who flaunted morals and conventional wisdom ("I have no need of a chart or creed"), betrayed or used everyone close to him/her ("those landsmen who you but lately knew/Were left stranded on the lea") and lived life heedless of the consequences ("the flag you flew was a pirate cross"). The narrator tried to convince this person to change his/her ways, but gave up in frustration ("you paid no mind to the warning signs") and is now watching from a distance as the consequences of his/her actions catch up with him/her: "Don't call my name when your ship goes down"
[Edit: Improved interpretation.]