The answer to this question can be found at the beginning of Act III scene 1, when Solanio and Salerio meet to discuss the fortunes of their friend Antonio and in particular the way that one of his ships has been shipwrecked. Note what Salerio says:
Wh, yet it lives there unchecked that Antonio hath a ship of rich lading wrecked on teh narrow seas--the Goodwins, I think they call the place, a very dangerous flat, and fatal, where the carcasses of many a tall ship lie buried, as they say, ifmy gossip Report be an honest woman of her word.
"The Goodwins" refers to Goodwin Sands, which lies off the Kentish coast near the Thames estuary in England. Therefore we are told as the rising action increases the tension as we fear Antonio might default on his loan that one of his hopes of gaining back his wealth ten-fold has no been wrecked. Being a merchant at this time was a very risky venture, as more often than not a high proportion of ships failed to return successfully.