The area below the torpedo launcher where the interhull meets the engineering hull is a very tricky zone to map because the hull lines have to run straight through along the y axis. The engineering section has to be mapped in a planar fashion from the top down, whereas the interhull has to be mapped planar from a side view.
As I recall, when it was mapped it was not possible to map the hull lines appear the same size, so I actually ended up pinching on of them at the end so that when it met the other one from the other map, they would appear to be the same size. To clarify, this was a result of the way that mapping distorts textures depending on the shape of the surface being mapped.