If you like going down to the sea in ships, but don't want to go too far, then you may well like to vary your holiday a little by taking one of the various short cruises available from various parts of Crete.  Usually to one or more of the various small islands sitting close inshore.  Remember though, if you insist on hiring one of the smaller craft available for a brief charter, to ask if the vessel has a toilet aboard!  They usually do have, but I already know that one I am planning to hire is not so equipped...
From Chania...
At least one company operates every day from the old harbour using a glass-bottomed boat for short 3 hour cruises and a larger motorised catamaran  for 5 hour cruises.

The glass bottom boat 'Evagalos I' leaves three times daily for a cruise around the nearby small islands of Glaronisi; Theodorou; and Lazaretta just off Agia Marina and Platanias.

Evagalos I
For the more nervous among us, (and being told that the boat has a glass bottom does not always make for a feeling of high security), the boat has is a glass viewing panel fitted which is probably stronger than the hull itself, so that passengers can view the marine life below.  Quite a treat for kids of any age!  You also get the chance of a swim at Theodorou island and a unique opportunity to view though the glass bottom a WWII aircraft sunken off the island.  Something to tell the neighbours when you get home.  The current departure times for Evagelos I are 10.30am;  2pm; and 6pm.  The latter is good if you like sea-borne sunsets.
Evagalos II
The same cruise as Evagelos I every day, but a more leisurely 5 hours, except Saturday.  On Saturday the boat leaves at 9.30am for the ancient beach and city of Diktynna (Diktina) at the tip of the Rodopos peninsula, returning at 6.30pm in the evening.  This is your chance.  If you are not an intrepid motorist or hiker, you won't find a better way of getting to Diktina.  A chance to reach this ancient area, the site of the temple shrine of
Diktynna, which shows traces of ancient dwellings as old as the 9th Century BC, should not be missed if you can help it.  Diktynna was Britomartis, daughter of the Greek God Zeus.