The offer of a position on the Beagle, which Charles received on August 30, 1831, came through his advisor, Henslow, at Cambridge. Henslow himself had been invited to be the naturalist for the ship, but had turned down the opportunity. The voyage had been commissioned by the government to map the coast of South America and was being captained by Robert FitzRoy, a 26-year-old gentleman who had led a ship to South America the year before. FitzRoy was eager to have the companionship of someone who, unlike the sailors and officers of the ship, was of his social class. A gentleman naturalist would fit the bill perfectly, providing companionship while increasing the usefulness and prestige of the voyage. Most well-established naturalists, like Henslow, had proven to be busy or disinclined, so the job had fallen to the promising but inexperienced Charles Darwin.
Unfortunately, there was a hurdle to be crossed before Charles could sign on. He needed his father's blessing. Robert Darwin, however, had had enough of Charles's indolence. To Robert, it looked the attempt to make Charles into a respectable clergyman was about to fail as quickly as had his attempt to make him a physician. In his eyes, the voyage was nothing but a dangerous and unprofitable adventure that would do hurt Charles's chances for a solid career. Furthermore it looked suspicious to Robert that other, better-known naturalists had turned down the opportunity; there must be something wrong, he argued, with the ship or its captain.
With a heavy heart, Charles rode to Maer to talk to his uncle Josiah. Josiah agreed with Charles that this was a once-in-a-lifetime opportunity; there was certainly no reason to think that the voyage would interfere with his career when he returned. In the meantime, it would provide an unparalleled opportunity to see the world and maybe even do some science in the process. He wrote a letter to Robert and sent it off immediately, enumerating the reasons why the voyage would be good for Charles. Charles returned to The Mount to find that Robert had been convinced. If Josiah was in support of the trip, Robert could hardly remain against it.
Overjoyed, Charles began to prepare frantically for the voyage. The ship was scheduled to depart in a couple of weeks. But as he prepared, he received a shattering note: it turned out that there had been a miscommunication and FitzRoy had already promised the position to a friend. Charles would get the position only if the friend refused. Despite this setback he rushed to London to meet FitzRoy for an interview. FitzRoy seemed temperamental, but they got along reasonably well, and in the end FitzRoy's friend declined. Charles was given the position. He also found out that the trip was more likely to last three years than two, and that he would have to pay his own way.
Having secured the position, Charles made a last farewell trip to visit Woodhouse, where he found out that Fanny Owen's engagement had just been broken, news that might have gladdened him in another situation He also visited Maer and The Mount to bid adieu to the Wedgwood relatives and his father and siblings. On October 2, 1831, he returned to London where he bought supplies and consulted with local taxidermists and naturalists on how best to preserve and return the samples he collected while on the voyage.
The ship's departure was delayed several times while the ship was prepared. Poor weather delayed the crew even more. Finally, on December 10, they set sail, but were soon turned back by gale winds that rocked the boat and left Darwin miserably nauseated. On December 21, they had what looked like perfect weather and tried again. It was a bad start: FitzRoy almost immediately ran the ship aground, but fortunately nothing was damaged and they quickly set sail again. But when Darwin woke up after his first night's sleep on the ship, he found that they were headed back to England. A wind from the southwest was pushing them back to where they had come from. Finally, after a muted Christmas spent at the port, the ship left on December 27, 1831.