Shipbucket

well, check the OP then .
and of course you get an longer car deck on an smaller ferry if you use an double ender both space and loading facilities get a lot smaller then. so, I think you have answered your own doubts already here

Length
Over all (including protrusions): 950 ft (289.56 m). Exceptions:
Container ship and passenger ship: 965 ft (294.13 m)
Tug-barge combination, rigidly connected: 900 ft (274.32 m) over all
Other non-self-propelled vessels-tug combination: 850 ft (259.08 m) over all

Width
Width over outer surface of the shell plating: 106 ft (32.31 m). General exception: 107 ft (32.61 m), when draft is less than 37 ft (11.3 m) in tropical fresh water.

Draft
39.5 ft (12.04 m) in Tropical Fresh Water (TFW). The name and definition of TFW is created by ACP using the freshwater Gatun Lake as a reference, since this is the determination of the maximum draft. The salinity and temperature of water affect its density, and hence how deep a ship will float in the water. Tropical Fresh Water (TFW) is fresh water of Gatun Lake, with density 0.9954 gms/cc [0.9954 g/cm3], at 29.1 °C (84 °F).[3] The physical limit is set by the lower (seaside) entrance of the Pedro Miguel locks. When the water level in Lake Gatún is low during an exceptionally dry season the maximum permitted draft may be reduced. Such a restriction is published three weeks in advance, so ship loading plans can take appropriate measures.

Doesn't IMO regulations require enough liferafts for 125% of the crew and passengers on each side?