Hi, Bob.  My apologies for taking so long to get back to you.  Just two weeks until the election... *sigh*

First off, I want to clarify one point.  STF does have an Explorer class vessel and has for some time: The Viking.  It may not have looked like it, however, as I realized last night that there had been an error copying the spec from the old TM into the Library that caused its crew complement to be listed wrong.  See:

http://www.star-fleet.com/ed/tm/viking.html

for the old copy to confirm.  I've corrected the error, so the Library copy now reads correctly.  It has a crew complement of 1000, making it a large Explorer roughly the size of and mission profile of the Galaxy.  My apologies for the long-standing error.  (If you find any others, please let me know!)

Also, on a side note, with all the time Bret's spent in the EDept he should know that a Heavy Cruiser is not the same thing as a large Explorer.  :-)  A Heavy Cruiser, (a Medium-sized General/Exploration vessel) would compete with a Light Explorer (Large General/Exploration), while both Viking and Columbus are Heavy Explorers, by our definitions, like Aurora and Galaxy before them.

So I have to first once again encourage you to go with a Viking if you're looking for a Galaxy-esque exploration vessel.  It even has an "Orion Pirates of the Carribbean" area on it (which I think Shalon added just to see if he could get it by us, which he did) for the whimsically inclined.  (You don't need the spec's permission to have humorous areas, if that's the desire, mind you, as long as they don't contradict the spec.)

If you want to go with a new design, that's allowable once we have at least one of priority one vessels taken care of (Cruiser and Surveyor).  It would also need to sufficiently differentiate itself from Viking, which means not a Heavy Explorer.  I like the idea of a sub-light "drop ship", and in fact just pitched that to Jen for a Surveyor in the EDept. ;-)  

While I'd rather you go with an existing design, if Bret wants to try and submit another design that is distinct from what's already available, though, I am willing to give it due consideration as a new design, time permitting.  (To be fair, the heavy cruiser / light explorer classification is a place I'd like to see another option made available, but it's not a high-priority need.)