The simile that describes the beam of wood that Odysseus found in the cave is the following:
<em>it was like a mast </em>
<em>a lugger of twenty oars, broad in the beam—</em>
<em>a deep-sea-going craft—might carry: </em>
<em>so long, so big around, it seemed.</em>
A "mast" is an upright post found in most ships or vessels, especially in those that use sails. The simile explains that this beam of wood resembled the mast of an enormous ship as it was very long and broad.