Why did Lemuel Gulliver originally go on his first voyage?

The surgeon Gulliver was apprenticed to recommended him to work as a ship's surgeon. Gulliver, always believing he would travel, accepted the job.

"........ I was bound apprentice to Mr. James Bates, an eminent surgeon in London, with whom I continued four years. My father now and then sending me small sums of money, I laid them out in learning navigation, and other parts of the mathematics, useful to those who intend to travel, as I always believed it would be, some time or other, my fortune to do. When I left Mr. Bates, I went down to my father: where, by the assistance of him and my uncle John, and some other relations, I got forty pounds, and a promise of thirty pounds a year to maintain me at Leyden: there I studied physic two years and seven months, knowing it would be useful in long voyages.

Soon after my return from Leyden, I was recommended by my good master, Mr. Bates, to be surgeon to the Swallow, Captain Abraham Pannel, commander; with whom I continued three years and a half, making a voyage or two into the Levant, and some other parts."