On page 61, Santiago says, "He thought of how some men feared being out of sight of land in a small boat and knew they were right in the months of sudden bad weather. But now they were in hurricane months and, when there are no hurricanes, the weather of hurricane months is the best of all the year. If there is a hurricane you always see the signs of it in the sky for days ahead, if you are at sea.... But we have no hurricane coming now." This shows that Santiago knows his work and monitors the weather closely. He knows that he will be safe and has nothing to worry about as there are no signs of inclement weather.
As for getting lost at sea, going so far out is a risk Santiago must take. He has to break his bad streak, and taking a risk like this is a necessary step towards achieving that.