Baudhayana Dharma-sutra, composed about 2,000 years ago, maybe earlier, lists this "Samudrolanghana" or "Sagarollanghana" as the first of many reasons for loss of castes (II.1.2.2).
Are there other dharma sutras prohibiting sea voyages?
The Manu Smriti also mentions undertaking sea voyage as a prohibited act. One becomes fallen/degraded by doing so.
For example, in the list of all the persons who are not considered fit to be invited in a Deva/Pitru related sacrifice, one who has undertaken a sea voyage is there.
3.157. He who forsakes his mother, his father, or a teacher without a (sufficient) reason, he who has contracted an alliance with outcasts either through the Veda or through a marriage,
3.158. An incendiary, a prisoner, he who eats the food given by the son of an adulteress, a seller of Soma, he who undertakes voyages by sea, a bard, an oil-man, a suborner to perjury,
3.166. A shepherd, a keeper of buffaloes, the husband of a remarried woman, and a carrier of dead bodies, (all these) must be carefully avoided.
Similar prohibition is held by the Usana Smriti (which is one of the 18 Smritis) as well. Following are the verses from the 4th Chapter of the Text:
One, who injures a friend ; one, who is deceitful ; one, who daily beats women ; one, who renounces his parents and preceptor ; as well as one, who renounces his wife; (32) One, who has no issue ; one, who gives false evidence ; one, who cooks food ; one, who lives by treating diseases ; one who goes to sea ; one, who is ungrateful ; one, who breaks a high way ; and one, who breaks an agreement ; (33) One, who is given to the vilification of the Vedas; one, who is given to speaking against the Deities ; one, who is given to speaking ill of the twice-born ; [all these] should be avoided in all rites appertaining to a S'raddha.