A quick look at the original Here suggests that the verse should be four lines of 11 syllables (with the exception of V1 l3: "Hush little baby, a story I'll tell," which was probably a slip)
So the additional verse is a little light on syllable count, and won't scan to whatever the tune is. So:

For four dread long years now we’ve not sighted land;
The captain, my captain's not fit to command;*
The winds they do roar and the waves they do roll;
Let’s seize this ship quickly and save all our souls!

*Sorry: quick riff on Walt Whitman's lament for Lincoln