Hi Jimbo,

There are two ferries from Kos Town to Kalymnos, so depending on the time of day one of these may be convenient. Check here for timetables:

http://www.openseas.gr/openseas/index.html

Kos will be listed under ‘Dodecanese Islands’.

The two ferries are ‘Dodekanisos Express’ (a catamaran, about 30min Kos to Kalymnos, departs around noon) and ‘Blue Star Diagoras’ (the large ferry, usually departs Kos town late afternoon / early evening, takes about one hour). But you will need to search for your specific date; unfortunately on certain days your only option may be Mastichari.

Good luck!