I have Gemini #987. I make 7 knts at 3000rpm. I routinely leave a board down as it helps with maneuvering, that's not it.
Raising boards might give me a 1/4 knots.
Make sure you raise them at survey just to make sure they work - it's a half day each of labor to re-rig them, and rebuilding is a bear.
If you made 3200 rpm as full throttle that is low, the engine is rated at 3600 and should make that with the normal 15x12 propeller.
Raise the drive leg and let the engine go to full rpm, pull out the manual and confirm my unloaded rpm memory - 3850.
Water is from the seacock in the starboard hull, there is no overheat danger running the engine with the leg up (and you want to test the pump / leg anyway).
If the boat capsized, and I'd love to hear that story, then the engine might be unable to deliver full power, and the propeller was changed to FOOL a buyer who wasn't paying attention to rpm vs speed. To my knowledge only 3 Gem's have capsized, all while being chartered bare boat. If that was a charter boat that 900 hours is a lie.
A Gemini with that weight loaded on it should float with at least one inch of hull between the water line and the two white drain holes from the rudder locker, check that - then take a torpedo (small) level and check for trim fore and aft. She could be low in the bow, or low in the stern.
If the flotation chambers where full you'd be WAyyyyy down in the water - that's over 2000 pounds even fresh. It would also be very noticeable if just one were flooded.
Almost all Gemini's list to port about 1 degree when no one is onboard - that's the battery weight. A 2001 105MC hull will have 1 inch of immersion per 450 pounds per hull (900 pounds to the inch if you load her exactly even).
Walking from one side to the other should rock the boat in her slip.
If the hulls are out of alignment that's a whole different problem and a walk away boat. I presume it would need lasers to determine that from the outside but a survey would find twisted bulkheads and beams. She'd also leak like a sieve because her deck would be warped.
Good luck - get the story on the capsize and shoot me a PM please.
If you need more input / feedback try the yahoo group or you can find me at Anything Sailing Forum
- same username, I'm a moderator over there.