Most couple nowadays cohabit before getting married. They do so mainly in order to find out whether they get along OK or not. In other words, they want to test their partners to see if they are good husband/wife material and somebody capable to form a family with.
Studies say, however, the cohabiting before marriage increases the risk of divorce, this is the so called 'cohabiting effect'. People who cohabit are less selective with choosing their partners and may later marry a person that isn't really right for them. There is a lower level of commitment in a cohabiting relationship that continues well into marriage and eventually can lead to divorce.
Two problems sailors faced before the 1400s was they did not have good ways of knowing where they were if they got beyond the sight of land. And 2 the maps were poor and the risk ships were to slow to mak long voyages