In Act I Scene iii of The Merchant of Venice, explain Shylock's words, " Yet his means are in supposition: he hath an argosy bound to Tripolis, another to the Indies; I understand, moreover, upon Rialto, he hath a third at Mexico, ...bond."
In The Merchant of Venice, obtaining a "pound of flesh" from Antonio will become Shylock's main aim as he strives to obtain satisfaction of his "bond." At this point in the play, Shylock is considering whether he should accept Bassanio's request and grant a loan of three thousand ducats to Antonio.
Antonio's means are "in supposition" meaning that there is some question about the imminent success of Antonio's latest ventures abroad. Shylock knows that Antonio's ships -"argosy"- are currently "bound" for other countries such as Tripolis, the Indies, England and Mexico as he has heard others talk "at the Rialto" - the meeting place where much gossip can be heard.
Shylock points out that ships are "but boards" making them susceptible to "winds and rocks" and sailors can only do their best as they are "but men." Then there are the "land-rats, water-rats....I mean pirates" who also put Antonio's ships at risk. "The peril of waters" and pirates are an enormous threat to the safety of any ships due to the weather and unscrupulous "rats" as Shylock calls them.
Having considered all this Shylock acknowledges that Antonio is still "sufficient" meaning that he is still a good credit risk and worthy of being granted a loan - a" bond."