Answer:
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.
Step-by-step 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.