Oh, sorry.
I knew there was something wrong.
That particular route is only OKW, SSR and DTD.
POR has its own boat that goes between the 2 PO resorts and DTD. The boats are identical to the pictures I posted (the decorations are a little different though). What you would need to do is get to DTD and from there, you can take the boat to POR.
At DTD, the boats all use the same docks, just different areas of the same dock/loading area. As you go down the ramp to the dock, a CM will ask you which resort you want (it is also marked on overhead signs).
The boats run until 9pm. If your trip to POR is going to be later than that, just get on a bus to DTD from PO. From there, it's an easy walk back to SSR or you can catch a bus to SSR.