Fairness Inspection, Punch List, and Dimensional Survey

Why Fairness Inspection Matters

A hull that looks complete is not necessarily a hull that is correct. Before any section leaves the assembly floor, every frame, bulkhead, keel line, and shell strake must be measured against the approved drawings and found to be within tolerance. This process is called a dimensional and fairness survey. Shipyards run this survey before they release a section to erection, and classification society surveyors (ABS) and Coast Guard inspectors may repeat it at the vessel level. Learning to do it accurately—and to document what you find—is a core shipfitting skill that carries directly into your NCCER Shipfitting credential and your ABS/USCG qualification work.

Setting Up a Baseline

Every survey starts with a reference. In a shipyard, the baseline is usually the keel centerline and a waterline datum scribed or laser-projected onto the structure. In the shop, your instructor will establish a baseline using a laser level or a taut wire at a known elevation. All subsequent measurements—frame spacing, bulkhead position, shell fairness—are taken relative to that baseline. Never measure frame to frame without first confirming that your starting point is correct; errors stack up fast.

Keel straightness is checked by running the laser or a string line along the keel bar and measuring any offset at each frame station. Any deviation from a straight line is recorded in inches and fractions.

Checking Frame Spacing and Bulkhead Position

The frame schedule on the construction drawing lists the designed distance from Frame 0 (the baseline frame or midship reference) to every subsequent frame. You verify these by measuring with a steel tape from the reference frame to each frame's forward face, recording actual versus nominal. In US shipyard practice, acceptable tolerance on frame spacing is typically within 1/8 inch of nominal for ordinary structure, but critical bulkheads (watertight, collision) may be held to tighter limits per the classification rules—always check the drawing notes.

Bulkhead position is checked the same way: measure fore-and-aft from the reference, then check that the bulkhead is plumb using a plumb bob dropped from the top flange or a digital level placed on the web. A bulkhead that is out of plumb transfers load incorrectly and may not fit the deck above.

Evaluating Shell Fairness with a Batten

A fairing batten—a long, flexible strip of wood or thin steel—is the classic tool for detecting humps (high spots) and hollows (low spots) in shell plating. You hold the batten against the shell surface in a fore-and-aft direction and observe where it lifts off or where light shows between batten and plate. The gap at the worst point is measured with feeler gauges or a small ruler. Acceptable shell fairness tolerances vary by vessel class; your instructor will specify the tolerance for this exercise. Any deviation beyond tolerance becomes a punch-list item.

A digital level placed on the shell in the transverse direction confirms that strakes are at the correct camber or deadrise angle.

Completing the Dimensional Check Sheet

Your instructor-issued check sheet has one row for each measurement point: frame number, design dimension, actual dimension, deviation, and a pass/fail column. Fill every cell. Leave nothing blank—a blank is interpreted as a missed measurement during an ABS audit, not as a passing result. Round all measurements to the nearest 1/16 inch and record fractions clearly (e.g., 3/16", not .1875"). Sign and date the sheet.

Writing a Punch List

A punch list is the formal record of every nonconformance found during inspection. Each item must:

• Identify the location precisely (frame number, strake letter, port or starboard, deck or keel)
• State the observed condition with a measurement
• State the required action

Standard industry format: Location — condition — action. Example: Frame 6 web height 1/4" low — grind weld, refit web, re-weld per drawing. Another example: Shell strake B, port, humped 3/16" at Frame 4 — jack against strong-back and re-tack before final weld.

Priority sequence in a production yard generally runs: (1) structural alignment issues that block the next assembly step, (2) watertight boundary deviations, (3) fairness defects in visible or hydrodynamic surfaces, (4) cosmetic issues. Your punch list should reflect this sequence—number items by priority, not by where you happened to walk during the survey.

Safety During the Survey

Housekeeping first. Tape measures pulled across a cluttered deck are a trip hazard; clear your path before you work. Eye protection is required on the assembly floor at all times—grinding and tacking may be occurring nearby. When using a laser level, never look directly into the beam; use the diffuse reflection on the target surface. When climbing on the mock-up to reach upper strakes or top flanges, use the designated step platform and maintain three points of contact. If any grinding or cutting is needed to correct a discrepancy during the session, lockout/tagout the grinder before changing discs and confirm PPE (face shield over safety glasses, gloves, hearing protection) before energizing tools.

Connecting to the Credentials

NCCER Shipfitting assessment tasks include inspection and quality-control procedures; knowing how to run a survey and write a punch list is tested knowledge. ABS and USCG surveyors use the same measurement logic when they witness weld qualification tests and inspect hull sections. Accurate documentation habits you build in this lesson translate directly to the audit trail those bodies require.