There is much need for Autonomous Underwater Vehicles (AUVs) for inspection and mapping purposes. Most conventional AUVs use torpedo-shaped single-rigid hulls, because of which their manoeuvrability is limited. Moreover, any increase in payload results in a larger hull size and the turning diameter, limiting its operation in constrained areas. To solve this problem, we develop a subsurface mapping AUV with a modular-split hull design that provides better manoeuvrability than conventional torpedo-shaped vehicles. At the same time, it has more agility than unconventional bio-inspired snake-like vehicles though their designs look similar. This approach makes it a hybrid solution between conventional torpedo-shaped AUVs and unconventional bio-inspired solutions. We also propose another advantage of the split-hull vehicle over the conventional ones by proving the existence of the optimum turning mode (n) for the 2-dimensional motion. The lateral action of the Coriolis/Centrifugal forces during the turning motion demands both surge and sway thrusters to follow the path without slipping. This issue makes it challenging to control the vehicle, affects its operation, and increases power consumption. However, with a split-hull design where the individual hulls can have different orientations, proper turning mode can significantly reduce the net lateral force acting on the vehicle and the corresponding sway thrust requirement. Thus, it is possible to eliminate the sway thruster in the case of a split-hull underwater vehicle which is impossible with a conventional design. We also consider the influence of other parameters, including the turning diameter, joint torque, and axial thrust, to select the best configuration for the specific operational requirement. The results of the analysis are validated through experiments with a fabricated vehicle named M-Hull. The insights developed here will help develop similar vehicles and guide operating them with minimal use of sway thrusters.