What is Ulysses' plea to his fellow mariners?

I think
that the fundamental pleamakes to his fellow mariners is to join him on a voyage where the
destination is uncertain, the results in limbo, but the journey is the epitome of being worthy. 
In the Homeric myth, Ulysses' ability to convince his fellow mariners to strive towards Ithaca,
towards home, had a directed end.  It proved to be relatively easy to galvanize men into action
with such a poignant and relatively simple selling point.  Tennyson's retelling of Ulysses is
much more complex.  Home has turned out to be something representing banality.  Home represents
the "idle" and "barren crags." The voyage and spirit of intensity that
accompanied it is lacking in home.  To this end, Ulysses' pleas are geared towards instigating
this spirit of what can be, of the conditional and of the possible, and of a realm where
directed end products are not immediately apparent:

For my
purpose holds/ to sail beyond the sunset, and the baths/ of all the western stars, until I die. 
It may be that the gulfs will wash us down.

This plea is
followed by a potential promise to meet Achilles once again and "touch the Happy
Isles."  It is this plea, one of adventure, challenge, and inspiration, that Ulysses offers
to his fellow mariners in the hope believing that consciousness can be an endeavor in which one
commits "to strive, to seek, to find, and not to yield."