Mostly straightforward - a Nantucket Sleighride happens when a (sperm) whale pulls a whaling boat through the water after the whale has been harpooned. The song focuses on a sailor leaving (presumably Nantucket) on a whaling voyage (first two verses and first chorus), out at sea on the voyage (third verse), and returning home (fourth verse and second chorus).
The song leans partly on Moby d*k, the story of a whaler out of Nantucket, which had a black first mate called Starbuck.
Much of the imagery is hard to unpick, and I would be interested to know anyone's thoughts.
Windlaced?
Reeds and drums? - why these musical instruments?
The significance of willow branches?