I'd go significantly bigger than 1,000 tons. The Atlantean sub tender is designed to service coastal subs (450 tons)in its hold. I'd say 4,000 tons is more practical for an MTB tender that performs a similar range of tasks for MTB's rather than subs.
A berthing area of 230x45 should be more than enough space for 6 MTB's of the current type operated by Mexico or most future designs. Crew accomidations for roughly 50 people and some sort of repair shop would also be usefull. Atlantis needs a new class of MTB tenders, perhaps co-operation with Mexico could result in a modification to the Patronus class design to service MTB's?
Patronus class, Multi purpose sub ship (MPSS ship)
Patronus(protector), Efficax (effective)
Atlantian Sub repair,depot,docking and salvage ship laid down 1924
Displacement:
6,761 t light; 6,914 t standard; 7,131 t normal; 7,277 t full load
Loading submergence 422 tons/feet
Dimensions:
325.00 ft x 64.00 ft x 20.00 ft (normal load)
99.06 m x 19.51 m x 6.10 m
Armament:
2 - 4.00" / 102 mm guns
4 - 3.00" / 76 mm guns
6 - 1.00" / 25 mm guns
Weight of broadside 121 lbs / 55 kg
Machinery:
Oil fired boilers, steam turbines,
Geared drive, 2 shafts, 3,750 shp / 2,798 Kw = 14.00 kts
Range 5,000nm at 10.00 kts
Complement:
388 - 504
Cost:
£0.824 million / $3.297 million
Distribution of weights at normal displacement:
Armament: 15 tons, 0.2 %
Machinery: 124 tons, 1.7 %
Hull, fittings & equipment: 3,623 tons, 50.8 %
Fuel, ammunition & stores: 370 tons, 5.2 %
Miscellaneous weights: 3,000 tons, 42.1 %
Metacentric height 2.7
Remarks:
Hull space for machinery, storage & compartmentation is excellent
Room for accommodation & workspaces is adequate
Ship has slow, easy roll, a good, steady gun platform
Excellent seaboat, comfortable and able to fight her guns in the heaviest weather
Estimated overall survivability and seakeeping ability:
Relative margin of stability: 1.02
Shellfire needed to sink: 12,214 lbs / 5,540 Kg = 381.7 x 4.0 " / 102 mm shells
(Approx weight of penetrating shell hits needed to sink ship excluding critical hits)
Torpedoes needed to sink: 2.8
(Approx number of typical torpedo hits needed to sink ship)
Relative steadiness as gun platform: 70 %
(Average = 50 %)
Relative rocking effect from firing to beam: 0.01
Relative quality as seaboat: 1.88
Hull form characteristics:
Block coefficient: 0.600
Sharpness coefficient: 0.45
Hull speed coefficient 'M': 5.16
'Natural speed' for length: 18.03 kts
Power going to wave formation at top speed: 40 %
Trim: 37
(Maximise stabilty/flotation = 0, Maximise steadiness/seakeeping = 100)
Estimated hull characteristics & strength:
Underwater volume absorbed by magazines and engineering spaces: 54.0 %
Relative accommodation and working space: 101.5 %
(Average = 100%)
Displacement factor: 212 %
(Displacement relative to loading factors)
Relative cross-sectional hull strength: 2.15
(Structure weight / hull surface area: 171 lbs / square foot or 836 Kg / square metre)
Relative longitudinal hull strength: 4.72
(for 14.00 ft / 4.27 m average freeboard, freeboard adjustment -0.15 ft)
Relative composite hull strength: 2.33