You can:
~Take the bus to DHS from Poly and transfer to the boat. Travel time to Yachtsman at the Yacht Club, assuming you catch a DHS bus fairly quickly, will be about an hour.
~Take the Monorail to MK from Poly and transfer to a bus to the Yacht Club. Travel time, assuming a Yacht Club bus arrives fairly quickly, will be about an hour. Maybe a little less, depending on how fast you walk (from monorail station to bus station in front of MK) and whether you catch a monorail quickly when you leave the Poly.
~(This one assumes you have parkhoppers, or that you were in Epcot earlier that day) You can walk to the TTC from the Poly, hop on the Epcot monorail, and walk through Epcot, out the back gate (International Gateway), and over the bridge to the Yacht Club. Travel time, assuming you catch the Epcot monorail fairly quickly and walk through Epcot at a fair pace, will be just under an hour, again depending on your average walking speed.
~You can take a taxi from the Poly to the Yacht Club. One-way, this is going to run about $20 and take about 20 minutes.