# Springline > Springline means a fixed point of curvature or change in direction of either structural objects or water vessels **Term:** Springline **Last updated:** 2026-07-29 ## Definition ## What Springline Means in a Contract In a contract, springline refers to a defined, fixed point at which a structural element or vessel hull transitions from a straight or vertical plane into a curve. It is a technical reference marker rather than a legal concept in itself, but it becomes contractually significant whenever accurate measurement, tolerance, or positioning of curved structures matters to the parties' obligations. Common examples include the springline of a tunnel, where the vertical side walls meet the curved arch or crown, the springline of a pipe or culvert, and the springline of a ship's hull where the flat bottom curves upward toward the sides. Because springline denotes a precise geometric point, contracts that rely on it typically do so to remove ambiguity about where one dimension ends and another begins. This matters in disputes over whether work was completed to specification, whether excavation or fabrication tolerances were met, or whether a vessel's stated dimensions match its as-built condition. ## How Springline Is Defined or Measured Springline is usually established by reference to engineering drawings, technical standards, or agreed survey methods rather than by a general dictionary definition. In tunnel and shaft construction, the springline is often set at a specified elevation above the invert (the lowest point of the structure), and this elevation becomes the datum from which curvature, lining thickness, and clearance are measured. In pipework, the springline may correspond to the midpoint of the pipe's diameter, used to calculate bedding depth and cover. For vessels, springline can refer to the line along the hull where the curvature of the bilge begins, which is relevant to calculating draft, freeboard, and stability characteristics referenced in charter or construction contracts. Because these measurements can vary by industry convention, contracts should specify which standard, drawing set, or surveyor's method governs the determination of springline, and whether any tolerance is permitted around that point. - Reference to a specific drawing number or engineering standard - Identification of the datum point used to fix the springline - Permitted tolerance or deviation from the stated springline - Method and timing of verification, such as survey or inspection ## Where Springline Appears in Agreements Springline most commonly appears in technical schedules, specifications, or drawings incorporated by reference into construction, engineering, and marine contracts. It is rarely found in the main body of an agreement but instead surfaces in appendices dealing with dimensional criteria, quality standards, or acceptance testing. These references are especially prevalent in the