Shipbuilding Drawings and Notation — Shipbuilding / Marine Fabrication

Objective. Students will correctly read and extract dimensions, weld symbols, material specifications, and part marks from a set of structural shipbuilding drawings with zero critical errors on a graded interpretation exercise.

Why Drawing Literacy Matters in Shipbuilding

Every plate you cut, every bracket you tack, and every weld you lay starts with a drawing. Shipbuilding drawings are legal documents that define exactly what gets built. A misread dimension or a missed weld symbol can cause structural failure, failed inspection, or costly rework. Before you ever pick up a chalk line or a grinder, you must be able to pull accurate information off the page with zero critical errors. That standard is not optional — it is what the NCCER Shipfitting credential and every naval architect, classification surveyor, and shipyard foreman will expect of you.

The Family of Shipbuilding Drawings

A complete drawing package for even a simple vessel contains several related sheets, each showing a different view of the same structure.

Lines Plan. This is the naval architect's master shape drawing. It shows the hull form as three families of curves: waterlines (horizontal slices), buttock lines (vertical fore-and-aft slices), and body plan sections (transverse slices viewed from the bow). Shipfitters use the lines plan to understand the three-dimensional curvature they must reproduce in steel.

Structural Profile. A side-elevation drawing showing longitudinal members — keel, keelson, longitudinal girders, and the positions of each frame station along the length of the ship. Frame spacing is always called out here, typically in millimeters or inches measured on the baseline.

Deck Plan. A top-down view of a single deck level, showing deck plating boundaries, openings, hatch coamings, and deck beams or longitudinals. Plate seam and butt joint locations are shown as dashed or solid lines with plate thickness noted in the panel or in a material schedule.

Shell Expansion. This is the shipfitter's workhorse drawing. The shell expansion "unrolls" the curved hull shell into a flat diagram. Each plate panel is shown with its true dimensions, material grade, and thickness. Seam lines, butt lines, and strake labels (bottom strake, bilge strake, side shell, sheer strake) are all identified. Weld types between panels are called out using symbols.

Frame Sections and Detail Drawings. Cross-sectional views at individual frame stations show the exact size, orientation, and connection details of floors, frames, longitudinals, brackets, and stiffeners. Detail drawings zoom in on complex connections such as bracket toes, insert plates, and penetration doublers.

Reading Title Blocks and Revision Clouds

Every drawing sheet carries a title block — usually in the lower-right corner — that contains the vessel name, drawing number, scale, units, revision letter, and the date. Always check the revision letter first. If you have Rev B on your bench and the yard has issued Rev C, you are working from an outdated document. Revision changes are highlighted on the drawing by a cloud shape around the altered area and a triangle with the revision letter.

Dimensions and Tolerances

Dimensions on shipbuilding drawings are given in one unit system — either US customary (feet and inches, fractions) or metric (millimeters) — stated in the title block. Never mix systems. Frame spacing is measured from center-line to center-line of frames. Plate thickness is a nominal value; the material specification (e.g., ASTM A131 Grade A) governs the allowable thickness tolerances from the mill.

When a dimension has a tolerance box (e.g., 12" ± 1/16"), the tolerance is the legally allowed deviation for fit-up. Exceeding tolerance is a nonconformance that must be reported to quality control.

Weld Symbols — AWS A2.4 Standard

All weld symbols on US shipbuilding drawings follow AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination. Every weld symbol has the same anatomy:

Reference line — a horizontal line that is the backbone of the symbol.
Arrow — points to the joint being welded.
Arrow side vs. other side — information below the reference line applies to the arrow side of the joint; information above applies to the other side.
Weld type symbol — placed on the reference line (fillet triangle, groove V, bevel, plug, etc.).
Size — number to the left of the weld type symbol gives the leg size for fillets or depth of preparation for grooves.
Length and pitch — numbers to the right give weld length and, for intermittent welds, the center-to-center pitch (e.g., 4-12 means 4-inch weld on a 12-inch pitch).
Tail — at the opposite end from the arrow; contains the welding process, specification, or procedure qualification reference when needed.
All-around symbol — a small circle at the arrow/reference line junction means weld completely around the joint.
Field weld flag — a filled flag at the same junction means the weld is made in the field (at the building way), not in the shop.

A fillet weld on both sides of a web would show two triangles, one below and one above the reference line, each with a leg-size number.

Material Specifications and Part Marks

Plate and structural material in commercial shipbuilding is typically specified to ASTM A131 (structural steel for ships) or an equivalent classification society grade. The grade letter (A, B, D, E, AH, DH, EH) tells you notch-toughness requirements. Higher letter grades are required for colder service and higher-stress areas such as deck edges and weather decks.

Every discrete part on a structural drawing carries a part mark (also called a piece mark): an alphanumeric code such as 3F-07 or PL-112A. Part marks link the drawing geometry to the bill of materials (BOM) — a table listing quantity, material grade, thickness, and sometimes weight for each part. When you fabricate a part, the part mark is stamped or marked on the piece so it can be tracked through the yard.

Safe Handling of Drawing Sets

Full-size structural drawings are large and awkward. Keep them away from grinding sparks, welding spatter, and wet surfaces — a damaged drawing delays the entire job. Never mark on the original; always work from a controlled copy. In areas where hot work is ongoing, store drawings in a tube or flat file away from the work zone. Be aware that drawing review at a welding station means you are near live electrical equipment and hot metal: wear your required PPE (safety glasses, gloves) even when "just" reading a drawing on the shop floor.

Key terms10

Shell ExpansionA drawing that mathematically unrolls the curved hull shell into a flat plan, showing each plate's true shape, dimensions, material grade, and thickness.

StrakeA fore-and-aft row of hull shell plates running the length of the ship, identified by a letter or name (e.g., bilge strake, sheer strake).

Frame SpacingThe center-to-center distance between consecutive transverse frames, called out on the structural profile and used as the primary grid for locating all other structure.

Reference LineThe horizontal backbone of an AWS A2.4 weld symbol from which all other weld information — type, size, length, and side — is read.

Part Mark (Piece Mark)An alphanumeric identifier assigned to each discrete fabricated part on a drawing, linking the geometry to the bill of materials and used for physical traceability in the yard.

Bill of Materials (BOM)A table on or accompanying a drawing that lists each part mark with its quantity, material specification, thickness or size, and sometimes weight.

ASTM A131The standard specification for structural steel for ships, defining grade letters (A, B, D, E and high-strength AH/DH/EH) with increasing notch-toughness requirements for more demanding locations.

Revision CloudA curved, irregular boundary drawn around any area of a drawing that has been changed in a new revision, accompanied by a triangle containing the revision letter.

Body PlanThe transverse-section view within a lines plan, showing the cross-sectional hull shape at multiple frame stations simultaneously — forward stations on one side, aft stations on the other.

Intermittent WeldA weld made in segments rather than continuously, described on a symbol by a length-pitch notation (e.g., 3-9 means 3-inch welds on 9-inch centers).

In class: Instructor walks through a sample midship-section drawing, pointing out the lines plan, structural profile, deck plan, and frame sections while students annotate a personal copy. · Students work in pairs to complete a scavenger-hunt worksheet requiring them to locate and record 20 specific data points—frame spacing, plate thickness, stiffener size, weld symbol, and material grade—from a three-sheet drawing package. · Individual written exercise: students sketch a simple bracket from a detail drawing, label all dimensions and weld symbols, and list the bill of materials for the part.
Materials: Full-size sample structural drawings (frame sections, deck plan, shell expansion), weld symbol reference chart per AWS A2.4, NCCER Shipfitting Module 1 textbook, pencils, ruler, highlighters
Check: Graded interpretation worksheet: students must correctly answer at least 80% of 25 questions covering drawing views, notation, weld symbols, and material callouts to pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.