I don't think there is a boat from the Poly to Ft Wilderness. There is a boat from the Contemporary &Wilderness Lodge to Ft Wilderness. And there is a boat from the MK to Ft Wilderness. From the Poly your best bet would be to go over to the MK and take the boat from there.
We did the opposite a few weeks back, FW to the Poly for an ADR. Took the boat to MK and we just missed the boat to the Poly from MK so we hopped on the resort loop of the monorail.