First off, let me offer some historically factual statements.
In the early 18th century, merchant ships flying the British Flag, which, of course, included the colonies, began hiring sailors from the West Coast of Africa. The reason for this being that they were not Crown Subjects and therefore not elligible for impressment into the Royal Navy.

It was immediately apparent that they were excellent sailors, dependable, resourceful and hard working. So, Thousands and thousands of Africans were eventually signed on to these merchant ships.

fact #2
Africans have a centuries old tradition of coordinating the efforts of more than one person, by singing. In the movie "Mogambo" starring Clark Gable, which was shot on location, there is a scene where several Africans are hauling a Rhinocerous out of a pit while singing a long drag chantey. In "Trader Horn", also shot on location, the Watusi People are portrayed by real Watusi, there are other examples, also they are paddling a boat while singing a chantey. Michael Caine's "Zulu" < also shot on location, the "Zulu" are portrayed by real Zulu. The move troop formations around, issue and acknowledge orders by singing.

In the 19th century, there were so many African Sailors employed on British and American ships that the State of South Carolina perceived them as a threat to "Domestic Tranquility" in the port of Charleston that they enacted the infamous "South Carolina Negro Seamen "act which stated that any Negro crewmen on ships entering Charleston Harbor had to be locked up in the city jail until their ship left port, and the cost of their upkeep was the responsibility of the ship's Captain. If the captain could not pay the required sum of money, his sailors would be sold into slavery to satisfy this debt.
This almost caused another war with the Mother Country when an English ship lost it's entire crew in this manner.

fact #3
Oliver Hazard Perry proved to the world that "Brittania did NOT rule the waves of lake Erie" with a force from my hometown, Newport, Rhode Island, consisting of (most historians agree)50% free African American Sailors.

The above facts are offered to show that there were a LOT of African and Afro American sailors on English speaking merchant ships. Now here comes my theory, The African sailors brought the tradition of singing to coordinate work aboard with them./ This quickly caught on when the other sailors saw how much smoother and easier the work became. Sthe ship owners, found that with this practice they could operate their ships with fewer crewmen and did so, thereby enabling them to cut costs (Crew requirements being the larges operating expense) and undercut the rates of every other country's ships. The result being that we, US and British, eventually had huge fleets of sailing merchant ships, their numbers being way out of proportion to our population.

The "call-response" form of sea chanteys, is exclusively African. There are no examples of this in any other English Language folk music. Irish people are extremely prolific and diverse in their composing folk songs. But, to them the music is an added bit of beauty to a poem. The tune makes the poem easier to recite. It also can add "dramatic " effect to the poetry. Here's one more bit of corellation. In the TV Movie "Mandella" , at the end of the movie, some zulus are singing a song with African words that is identical to "Little Sally Racket" and THE CAPE COD CHANTEY (ALSO KNOWN AS SOUTH AUSTRALIA) IS IDENTICAL IN FORM TO THE BANANA BOAT SONG. "Day Oh, Day oh" is exdactly the same melody as "Heave away me bully bully boys" (or "heave away you ruling king")