Parallel Mid-body
Length of hull where cross-sections are constant (the 'box' between the entry and run sections).
In practice
Visible in the cargo-plan; tank arrangement is straightforward over the parallel section, complex at the curved bow and stern tanks. Cargo officers plan even loading over the parallel mid-body to minimise hull bending.
Regulatory detail & full definition
The parallel mid-body is the length of a ship's hull over which the cross-sections are constant - the box amidships between the tapering entrance forward and the run aft. Its length is a key design choice: a long parallel mid-body gives more cargo volume per metre of ship and is favoured on bulk carriers and tankers, but it worsens the prismatic coefficient and slightly increases resistance. Fast, fine-form ships such as container vessels therefore have short parallel mid-bodies, while slow, full-form bulkers have long ones.
Related
Source: Standard naval architecture
High confidence
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