Joe,
The classic get-'em-to-sing-when-they-don't know-the-words song is The Goldfish: (to the popular version of Auld Lang Syne)


THE GOLDFISH

The goldfish, in his little bowl
Swims round and round and round,
And round and round and round and round
And round and round and round.
    And round and round and round and round
    And round and round and round
    And round and round and round and round
    And round and round and round.

And when his mating time comes due
He does not leap nor bound,
He just swims...etc

And when the crack of doom is heard
You know where he'll be found,
Just swimming round etc.


Or you could use just about any sea chanty, or any union song or most simple gospels.