The keen is a part of the boat that is used to support the boat, as in the poem the keen is used as a symbol of a strong nation.
Explanation:
The first use of the keel represents stability that the boat needs to have on the water. The other use of keel is as a synecdoche.
In Witman’s poem, the steady keel is a symbol of a strong and stable nation, that although has to pass many obstacles it maintains itself strong. It represents the whole boat that carries the nation on its deck.
They had a happy ending because they felt like they got justice and free rain over the socs when they won the battle and like they avenged what Johnny did.