How many gauging points per plate?
In sound plating the rule is one representative point per plate — not five. The five-point pattern is a densification standard, triggered by condition, not the default.
The short answer
- General plating: one representative reading per plate.
- Deck, bottom and wind-and-water strakes: at least 2 points on each plate, at the 1/4 extremities or in areas of average corrosion.
- “Selected plates”: one point on one plate out of three.
- Transverse section: one point on each plate of every longitudinal member; longitudinals measured on web and flange.
- Substantial corrosion or suspect area: the five-point pattern replaces the single reading.
Sound plating: one point, taken where corrosion is average
A single representative reading per plate is what the strength assessment needs. The point is chosen in an area of average corrosion, not the worst spot and not the cleanest one — the reading stands for the plate. UR Z10.2 R37
Three plate families are the exception and take two points each: deck plating, bottom plating and the wind-and-water (boot-top) strakes. The two points sit at each 1/4 extremity of the plate, or in representative areas of average corrosion. A.1049(27) Ann.1
Where the rule text says “selected plates” it means exactly one single point on one out of every three plates, chosen in representative areas. Reading “selected” as “all, sampled densely” is the most common way a report comes back from the office. UR Z10.2 R37
Transverse sections: one point per plate, web and flange on every longitudinal
A transverse section is a cut perpendicular to the centreline taking in all longitudinal members: deck, side, bottom, inner bottom, hopper, top-wing and longitudinal bulkheads. Each plate gets one point; each longitudinal and girder is measured on both web and face plate. At least one section must lie within 0.5L amidships. A.1049(27) §1.2.6
How many sections depends on the ship's age, not on the plate:
| Age of ship | Sections | Also gauged |
|---|---|---|
| ≤ 5 yr | 0 | One section of deck plating, full beam |
| 5 – 10 yr | 1 | Each deck plate; selected wind-and-water strakes outside the cargo area |
| 10 – 15 yr | 2 | Each deck plate; all wind-and-water strakes in the cargo area |
| > 15 yr | 3 | Each deck plate; each bottom plate; all wind-and-water strakes, full length |
Source for the whole table: A.1049(27) Ann.1 UR Z10.2 R37 · CSR tankers over 10 years follow a denser table: within 0.1D of deck and bottom, every longitudinal and girder is gauged web and face, plus one point on every plate between longitudinals.
Side shell frames: five points on the web, by rule
Cargo-hold frames in single-side-skin bulk carriers are the one place where five points are the baseline, not the exception. On the web, a five-point pattern is taken over the depth of the web in Zones A, B and D — Zones A and B (the lower bracket and lower part) being the critical pair — and the average reading is reported. Zone C takes three readings along its length, averaged, expanded to five if general corrosion is present. A.1049(27) Ann.15
At sections a) and b): at least 2 readings on the flange/face plate per section, plus at least 1 reading of the attached shell plating on each side, fore and aft, of the frame. Where pitting intensity exceeds 15%, clean a 300 mm diameter area to bare metal, gauge the five deepest pits and record the least. A.1049(27) Ann.15
How many frames depends on the renewal survey number: RS No.1 all frames in the forward hold at representative positions plus selected frames elsewhere; RS No.2 25% of the forward hold; RS No.3 all forward-hold frames plus 25% in each remaining hold (50% for bulk carriers ≥ 100,000 dwt); RS No.4 and after, every shell frame in every cargo hold. If one frame in a hold needs renewal, all frames in that hold are gauged. A.1049(27) + Z10.2
When five points become mandatory everywhere
Substantial corrosion is the switch. Pre-CSR ships: wastage in excess of 75% of the allowable margin. CSR ships: a gauged thickness between tnet + 0.5 mm and tnet. Find it at any survey, at any age, and the extent expands. A.1049(27) §1.2.9
- Shell plating: the suspect plate plus the four adjacent plates, five-point per panel between longitudinals.
- Bottom, side-shell and inner-bottom longitudinals: minimum 3 longitudinals in way of the suspect area — 3 readings across the web, 3 on the flange.
- Inner bottom (tank top): the suspect plate and all adjacent plates, five points per panel between longitudinals over 1 m length.
- Lower stool: bands within 25 mm of the welded connection to inner bottom and to the shelf plate — five-point between stiffeners over 1 m length.
- Suspect areas are re-gauged at every subsequent annual and intermediate survey until rectified.
Source: A.1049(27) Ann.10 UR Z10.2 Tbl VIII
What goes on the sheet
Longitudinals carry two values, web first, flange second, separated by a slash. The office reads the order from the magnitudes if you reverse them — and then telephones you.
11.8 / 15.9 single reading, web / flange 11.5-12 / 16.5-17 range — acceptable on the departure draft
Where a five-point pattern is taken, record all five when the spread is wide. The spread is information, not noise: it is what tells the office whether the plate is evenly wasted or pitted.
Marking these patterns on the drawing
Draft Operator places points on the shell expansion on a tablet and writes the web / flange pair in one gesture — ⊞ Pattern → Plate ×5 for the densified areas.
Open Draft OperatorSources
- A.1049(27) Ann.1/10/15IMO Res. A.1049(27) — 2011 ESP Codeofficial text ↗
- UR Z10.2 Rev.37IACS — Hull surveys of bulk carriers, Feb 2023index entry →
- UR Z10.5 Rev.20IACS — Double-skin bulk carriers, Feb 2023official text ↗
- Rec 76 Rev.2IACS — Guidelines for surveys, assessment and repair, 2017 (current)official text ↗
- MSC.168(79)IMO — TM of side shell frames and brackets, as carried into ESP Annex 15official text ↗
- CSR ConsolidatedIACS CSR BC & OT, consolidated 2025-07-01official text ↗
Class-society and IMO documents are indexed and linked, never re-hosted. Where a class rule is stricter than the IACS baseline, the class rule governs.