The walk from PBH to HRH is maybe 5 minutes or so (probably less distance than walking from the BWI to the YC). It's a nice walk. PBH and RPR are on opposite ends of the resort complex, however, and is probably a 20 minute or so walk end-to-end (if you've walked from the BWI to MGM, it's much shorter than that to give you a comparison).
Boat transporation is available from each resort to City Walk. So, if you're staying at PBH, you would take the boat to City Walk, disembark, and then catch the boat to RPR. I would not take the boat from PBH to HRH ... it would be MUCH quicker to walk since you have to change boats at City Walk. There is bus transportation that takes you between the resorts, however. Can't say that bus transportation is significantly quicker than the boat transportation though. The buses only hold about 12-15 people, and there may already be people on the bus when it stops at your resort.