A middle ship segment by definition has neighboring ship segments on opposite sides. If you can ascertain the direction of the middle segment (e.g. up/down or left/right), you can finalize segment wildcards on both sides of the middle.
Example
In the example above, the middle segment at (J,7) is obviously part of a ship going from left to right. Therefore, the square (J,6) is a left segment, while (J,8) can be finalized as a segment wildcard.