Even down here in Miami, where the Gulf stream is relatively close to land, it doesn't really pick up until at least a couple miles offshore, sometimes several, depending upon weather and conditions. You can pick a set distance like 1 mile offshore and you shouldn't have to deal with the stream too much. Following 40' will put you pretty close to shore in many places, if you don't want to sail that close to land. Depth wise, even 100' is not going to be in the stream much.