We are hoping to vist both Hydra (2 nights) and Nafplio (2 nights) after an island cruise. We disembark at Marina Zeas. Trying to figure out if we can get between Nafplio and Hydra. Any suggestions?
The Rome2Rio website is a good one to know about when you're tackling a thorny situation like this and don't know what modes of transportation may be available. I've found it not terribly accurate as to travel time and cost, but if you keep clicking and drilling down you'll usually find a link to the appropriate bus/train/ferry company website--possibly even to the specific schedule you're looking for.
It is also worth Googling things like "bus XX to YY" or "ferry "PP to QQ" to see if something else turns up. Occasionally there's an option that Rome2Rio doesn't know about.
In this case, it looks as if you may be stuck with a time-consuming, circuitous route, but perhaps Janet or Stan knows of a short-cut. They are both big Nafplio fans.
If you have Rick's Greece guidebook, see details for different options on pages 234 and 389. There is supposedly bus service between Nafplio and the ferry port at Ermioni, but maybe not very direct and sometimes requiring a taxi for one leg. Page 389 suggests a ferry from Athens to Hydra first, then picking up a rental car at Ermioni when you leave Hydra. Of course, if you're driving and visiting in the opposite order, you can leave a car parked at either Ermioni or Atochi ports.
Greece's KTEL buses have different (usually minimal) web sites for different areas and any published schedule should be re-checked locally. Rick's book also points you to this unofficial site: livingingreece.gr/2008/06/13/ktel-buses-of-Greece.