This could be a pun on a good sailor knowing the sea currents so well, he ‘has them in his pocket’.
But most probably it refers to currants/Zante currants, otherwise known as ‘Corinthian raisins’, of which Greece was historically a major cultivator.
The fruit itself has a mild relevance to the poem’s theme of sexual imbalance: although it is of dioecious species, with two sexes of the same plant growing male and female flowers on separate vines, the currant has relatively underdeveloped female organs.
The English word ‘currants’ comes from the fruit being sold from the Greek city of Corinth. The ancient Corinth, a hub for merchants and sailors, was also famous for its Temple prostitutes, numbering about 1'000 and contributing to the city’s opinion of being extremely expensive.
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