And explore who was preparing for a long dangers voyage during the age of exploration would worry most about

The storage of food and water first and foremost, as both spoiled on ships of the period. Secondly, one would worry about getting lost. No GPS and no actual way to tell where you are if a wind or storm blew you slightly off course.  Imagine how impossible it would be for a ship to travel in a perfectly straight line whilst traveling the entire span of the Atlantic, Pacific, or even smaller bodies of water such as the Mediterranean.