Been reading up/net surfing on Tophat 25's (while the monsoon rain falls here),
They have a wide range of uses/capabilities with most about Sydney and NSW coasts.
They displace 2.5 tons unloaded (over 3x bigger than an 1563, quite a huge step up!) and can load ~500kgs gear and stores, to displace 3 tons total.
They are even more variable than Investigators it seems. Three versions build, known as Mark 1, Mk2 and Mk3
Mark 1 - has the stepped dog house, strongest hull layup, lowest headroom and transom mounted outboard.
Mark 2 - Strong hull layup, long coach house and outboard well. cockpit floor raised a bit.
Mark 3 - Best headroom, nice fitouts, "youngest" (less old) equipment onboard, lighter hull layup.
The first 2 marks were often owner fitouts, the mark 3 usually factory fitout.
The distinguishing feature is the keyhole companionway with main traveller above (good to hang onto)
Nice 3/4 keels with fully attached inboard rudder,
Nice dinette to starboard, doubles as chart table
Cockpit has 2 storage hatches (much like an 1563)
Galley space to port forward of settee berth (maxie was standard factory stove)
Variations.
Forward starboard compartment (eg either a head, nav table or locker)
Storage setups (lockers, shelves etc)
Galley fitout details (sinks/water, stoves, racks)
Engines (from inboard diesels to outboards, any make/model, seems like 6-15 hp). Inboard diesels for offshore serious any weather/anytime, well outboards for coastal fair-wind day hoppers, transom outboards for harbour sailing.
Rig set-ups vary allot. Some run halyards aft, some don't. Some have roller furlers, some don't. Some have double slab reefing/ lazyjacks etc others don't. Some have anchor winches, others don't. Some have autohelms (ST1000 or ST2000 size usually)
Some have cruising fitouts (eg solar panel rack, bimini's, spray-dodgers, sail UV edge strips, sail-covers, more/better navigation and safety gear) others have minimal.
The "Top hatters" have an online forum
http://www.tophatyachts.com/