(Portland, OR)  --  Authorities say they've suspended their search for a Portland man who's thought to have drowned in the Columbia River.  Officials say John David Martin tried Wednesday night to retrieve his boat, which drifted away from shore on Ackerman Island.  Multnomah County sheriff's deputies say Martin swam to and from his boat several times before disappearing underwater.  Authorities say additional recovery efforts are suspended until new information develops.