Skip,

Take another look at the product link that I posted. It supposedly has
two transmitters and a "Bridge Repeater" mode which may do what you
want. PoE cable length should not be a problem because all of the
commercially available products that I've seen sense voltage drop
automatically and compensate accordingly.

Ignore the Pringle can antenna recommendations. As you probably know
directional antennas are unsatisfactory for anchored boats because of
swinging.