I believe this is referring to Robert Blake, however, Sgt. William Harvey Carney was awarded the MOH for an action on July 18 1863 while Blakes was awarded for an action on December 25 1863 but as the question asks for a Union Sailor I'll go for Robert Blake.
The 1st African-American to have the “Mettle” to win the “Metal” that is formed to make the “Medal” of Honor was at least according to Wikipedia and fits the clues (1811-1886 & Union Sailor) was Aaron Anderson (his birth name) or perhaps Aaron Sanderson.
The Wikipedia article on Aaron Anderson indicates that he was the first African-American to receive the Medal of Honor, and also indicates that he was born in 1811 and died on 9 January 1886.
The Wikipedia article listing African-American Medal of Honor recipients indicates that Robert Blake, also a sailor, received his Medal of Honor in 1864, which would have been prior to Anderson's receiving of the award. However, neither Blake's date of birth nor his date of death are known, so he apparently is not the intended answer to this question.