when did it become independent?
27 October,1979.
Saint Vincent (Antilles)
Following a referendum in 1979, St. Vincent and the Grenadines became the last of the Windward Islands to gain independence, on 27 October 1979. 
what is the flag of saint vincent and the grenadines? A Canadian pale triband. who designed it? Julien van der Wal . did it face any legal issues? Yes, as it is used as a flag of convenience by foreign merchant vessels. what was the reason for such adoption by these merchant vessels? It offers many advantages for them, such as less expensive fees and lax rules regarding crew, safety, and the environment. what were the working conditions? Low wages, long hours of forced work, minimum social standards, failing to pay the crew, abandoning the crew in distant ports, and low safety standards. did this business practice had to conceal their ownership? Yes, as it makes it hard to track the beneficial owner. who controls the port state? It varies from place to place. For example the US Coast Guard handles port state control inspections in the US. which country used the flag that julien designed? Saint Vincent. can you describe the history of it a few words? It was previously called "Hairouna". This place was used for slaving expeditions by Columbus and the Spanish conquistadors.
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Saint Vincent (Antilles) [SEP] Self-rule and independence
St. Vincent was granted associate statehood status by Britain on 27 October 1969, giving it complete control over its internal affairs. Following a referendum in 1979, St. Vincent and the Grenadines became the last of the Windward Islands to gain independence, on 27 October 1979. It celebrates Independence Day every year on 27 October.