CAP Thickness Measurement · Rotterdam, Netherlands

Condition Assessment Programme gauging for older tankers and bulk carriers calling at Rotterdam

Charterers and oil-major vetting teams ask more questions about a fifteen-year-old tanker than about a five-year-old one, and a Condition Assessment Programme rating is how an owner answers them. Rotterdam is where many of those answers are built: ships idle on lay-by berths between nominations, tanks get cleaned for the next grade, and the Botlek docks are close. The classification society issues the rating. We supply the measurement behind it, travelling from India to the ship and gauging in the order the society's engineers will need.

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Use the idle days between nominations

A tanker waiting on a lay-by berth or buoy for her next cargo has tanks that can be cleaned, ventilated and opened. CAP-level gauging fits that window better than a terminal call, when cargo work leaves no tank free.

Data laid out for the society's engineers

The society's CAP team assesses strength from the readings. They arrive grouped by tank, structural member and strake, with the corrosion pattern noted, so the engineers can use the figures directly rather than reorganise them.

Know the likely grade before booking

Pre-CAP gauging of the tanks most likely to limit the rating shows an owner whether the programme is worth starting. If the ballast tanks are already beyond margin, that is known before the society is engaged.

Why do owners prepare for a CAP rating in Rotterdam?

The vetting pressure is felt most on ships trading into the Europoort and Botlek terminals. Major charterers and terminal operators screen older tonnage on the strength of its steel, and an Aframax or product tanker with no recent, traceable gauging is the first one set aside when a cargo is nominated. A rating from the society gives the ship a record that stands up to the question.

Rotterdam also offers something that terminals elsewhere do not: patience. The port has lay-by berths, buoys and anchorages where ships wait for cargo or a yard slot, and the same ship may spend several days between a discharge at Botlek and her next loading. That waiting time is when a tanker can be cleaned and made available for close-up survey, and it is when most pre-CAP gauging is arranged.

The ships are mostly crude and product tankers, with chemical tankers from the Pernis and Botlek jetties and Panamax or Capesize bulk carriers that qualify for a CAP-type assessment on the society's terms. The older the ship and the more heated or aggressive her cargo history, the more the ballast tanks and the bottom structure dominate the plan.

Where can CAP gauging be done on a ship at Rotterdam?

Close-up survey and gauging in cargo and ballast tanks both need access, and access needs time. A lay-by berth is the practical place for a first pass: the ship is idle, staging can be rigged in ballast tanks, and ventilation and gas-freeing can run without a cargo programme pressing on the crew. A buoy works the same way for a ship that does not need shore services.

For the full programme, the yard decides. If the ship is booked into a Botlek dock for her renewal survey, the CAP work is folded into it, and the society's surveyor sees the same tanks once. If the ship is trading and only the assessment is wanted, the team gauges tank by tank at the lay-by berth, with the society attending when the staging is ready.

Terminals are less useful. At an oil jetty the terminal's rules limit what can be done during cargo handling, and cargo tanks stay closed until the ship has finished and been cleaned. We use a terminal call only for the deck, deck piping and accessible topside spaces, under a permit.

How is CAP gauging scoped for a tanker here?

The scheme belongs to the society, and each society publishes its own procedure, so we scope against the one the owner has chosen. In outline, the assessment looks at the main structural members in the cargo and ballast tanks, the bottom and side shell and the deck, with readings taken in considerably greater number than a routine survey asks for. The aim is a picture of how much steel remains where the hull girder takes its loads.

We start from the ship's last gauging reports and from the society's list of areas of concern. Tank by tank, the plan marks strakes, longitudinals, web frames and bulkhead plating, and fixes the reading pattern across each. Where earlier surveys recorded pitting, the pattern is denser. Where a tank was recoated after the last survey, we note it, because bare readings and coated readings are not treated alike.

Order of work depends on tank cleaning. Cargo tanks come after cleaning and a gas-free certificate; ballast tanks are available as soon as they are emptied. We normally begin with the ballast tanks, which dominate the findings on older tankers, and move to the cargo tanks as they become available. A schedule agreed with the chief officer in advance avoids the common failure of a team waiting on a tank that has not been washed.

What does CAP gauging typically find on older tankers?

Ballast tank structure next to heated cargo is the usual limiting area. Bottom plating, the lower part of longitudinal bulkheads and the stiffener flanges lose steel faster than the rest of the tank, and the pattern repeats from frame to frame. Gauging it in a grid shows whether the wastage is uniform, which the strength calculation can accommodate, or concentrated in a few strakes, which cannot.

Cargo tanks on crude carriers show their own pattern: pitting on the bottom, particularly where water settled, and grooving along the toes of longitudinals. Deck plating loses thickness in way of the tank-cleaning machine openings and the vent heads. On product and chemical tankers the corrosion is often milder in the cargo tanks but heavier in the ballast spaces, because coatings were meant for cargo and neglect shows in the water tanks.

Bottom plating and lower bulkhead strakes beside heated cargo, measured in a grid.
Pitting on cargo tank bottoms, mapped by reading density.
Grooving along longitudinal toes and web frame welds.
Deck plating wastage at tank cleaning openings and vent heads.
Ballast tank coating condition recorded beside each patch of readings.

How do you plan CAP gauging for a Rotterdam call?

Tell us which society and which scheme, the ship's last survey dates and the window you expect at Rotterdam, even if it is only a rough range. We ask for the tank plan and the previous gauging reports, then agree which tanks will be gauged first. The ship's agent submits the technicians' names for terminal or yard access, and for a lay-by berth or buoy arranges the launch.

Because the team travels from India, each technician needs a Schengen visa for the job, and that lead time is the real constraint on a short idle window. Where an owner expects the ship to be available but does not yet know the date, we plan a standby arrangement with visas ready, so the team can travel as soon as the nomination clears.

Pre-CAP gauging is best done at least one trading cycle before the society's survey, so that any tank found beyond margin can be repaired at the next docking rather than discovered during the assessment.

Where cap thickness measurement sits in the survey cycle

Class rules set the survey cycle, and the cycle sets how much gauging a ship needs. A superintendent planning a call at Rotterdam usually knows which survey is due; the table shows what the thickness measurement for each one typically involves. The exact extent comes from the class rules for the ship type and the surveyor attending, so the thickness measurement programme is agreed with the class before work starts.

Survey	When it falls	What the thickness measurement usually covers
Annual survey	Every year, within three months of the anniversary date	General examination. Gauging where the surveyor finds suspect areas or where substantial corrosion was recorded at an earlier survey.
Intermediate survey	In place of the second or third annual survey	Suspect areas, and on older ships and ESP ships selected ballast and cargo spaces with close-up survey; the extent grows with age.
Renewal survey No. 1	Around 5 years	The first full baseline: suspect areas and selected plating and stiffeners, usually with modest steel renewal.
Renewal survey No. 2	Around 10 years	Wider gauging of deck, bottom and side plating, transverse sections across the cargo area on ESP ships, and more close-up survey.
Renewal survey No. 3	Around 15 years	Extensive gauging of cargo and ballast tank structure and more transverse sections. The survey most likely to turn up steel renewal.
Renewal survey No. 4 and later	Around 20 and 25 years	Gauging extended to most structural members in cargo and ballast spaces. Charterers often add a Condition Assessment Programme.
Docking survey	Twice in each five-year period	Bottom and side shell, sea chests, rudder and stern area while the hull is dry; suspect bottom plating gauged.

How the job runs at Rotterdam

The sequence for a thickness measurement job at Rotterdam is short and written down, so the yard, the surveyor and the superintendent know who arranges what.

Send the vessel name or IMO number, ship type, class society, the survey due (annual, intermediate, renewal survey number, CAP or owner's condition survey), the port and dates, and the scope you expect.
We confirm the scope against the class rules for that survey, prepare the thickness measurement plan with frame and section references, and say whether the measurement will be credited to a class survey.
Mobilisation is planned around visa lead times and the vessel's schedule; the ship's agent arranges port access, and the yard or ship arranges staging, lighting, ventilation and gas-free certificates.
Gauging with calibrated ultrasonic thickness gauges: through sound coatings only where the gauge's through-coating mode has been verified on a coated reference, otherwise on cleaned bare steel, with every reading tied to its frame, strake and location on the sketch.
Readings are compared with original thicknesses as work proceeds; substantial and excessive corrosion and any cracks are reported to the attending surveyor and the superintendent the same day.
The final report is issued on the class thickness-measurement formats with sketches, a summary of locations exceeding the allowable margins, piping tables where piping was in scope, and the gauge calibration and technician certificates.

Who does the work, and when class approval applies

We send the team from India to the ship for each job rather than keeping staff at the port, and plan the mobilisation around visas and the vessel's itinerary. The work is planned and supervised by the founder, our Responsible NDT Level III (ASNT NDT Level III in UT, RT, MT, PT and VT, with more than eleven years of international field experience). Technicians hold certification under the company's written practice to ASNT SNT-TC-1A; Atlantis is ISO 9001 and ISO 14001 certified.

Thickness measurement that a classification society credits to a class survey has to be carried out by a firm approved by that society under IACS UR Z17. Atlantis is in the process of obtaining UR Z17 approval from DNV, Lloyd's Register and ABS. Until a certificate is issued, the readings we take are for the owner's own decisions, not for credit to a class survey, so tell us the vessel's class and the survey due when you enquire and we set the scope for the right purpose. Owner's and charterer's condition gauging, pre-docking steel estimates, pre-purchase and on-hire or off-hire gauging, and scrubber and piping condition checks between surveys do not need class approval.

Governing codes and standards

The classification society's published CAP procedure for the chosen scheme
IACS UR Z10.1 and Z10.4 for oil tanker hull surveys
IACS UR Z10.2 and Z10.5 for bulk carrier hull surveys
IACS UR Z10.3 for chemical tanker hull surveys
IACS Common Structural Rules for oil tankers and bulk carriers
ASTM E797 for manual ultrasonic thickness measurement

What you receive

Thickness readings by tank, structural member and strake, in the society's expected layout
Reading grids with positions marked on tank sketches
Corrosion pattern notes: general, pitted, grooved or edge wastage
Coating condition recorded beside each group of readings
A summary of members closest to allowable diminution for the owner's technical team

Industries served

Aframax and Suezmax crude tankers
Product tankers
Chemical tankers from Botlek and Pernis
Panamax and Capesize bulk carriers
Ageing LPG carriers
Offshore storage and support units

Frequently asked questions

Who issues the CAP rating for a ship gauged at Rotterdam?

The classification society issues it. Our work is the measurement: planning the gauging with the owner and the society, taking the readings and delivering them in a layout the society's engineers can use. We do not grade the ship and we do not decide what the rating will be.

Can CAP gauging be done while a tanker is working cargo at Europoort?

Only in part. The deck, deck piping and accessible topside spaces can be gauged under a terminal permit, but cargo and ballast tank work needs an idle ship. Most owners use a lay-by berth, a buoy or a dock stay for the tank structure.

What is pre-CAP gauging and when is it worth doing?

It is the owner's own gauging of the tanks most likely to limit the rating, taken before the society is engaged. It is worth doing when the ship is old, has a record of ballast tank coating failure or carried heated cargoes, because it shows whether repairs are needed first.

Why are ballast tanks gauged before cargo tanks?

They are available sooner, since cargo tanks must be cleaned and certified gas-free before anyone enters, and on older tankers they usually contain the thinnest steel. Starting there gives the owner the most useful information while the cargo tanks are still being washed.

How does the team reach a Rotterdam lay-by berth or buoy?

The ship's agent arranges access. For a berth that means gate passes and the technicians' names submitted in advance; for a buoy or anchorage it means a launch booked through the agent. We ask for these details when the window is known.

Does a CAP rating replace the renewal survey gauging?

No. The two are separate processes with different purposes, though they use similar readings. Where both fall at the same docking, the work is combined so tanks are opened once, but the survey and the assessment each remain the society's decision.

Can cap thickness measurement at Rotterdam be credited to a class survey?

Planning a survey or a drydock?

Send the vessel name or IMO number, the class, the survey due and the port. We reply with the scope, the mobilisation plan and a quote for that vessel.

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Request a ship gauging quote

Send the vessel name or IMO number, the class society, the survey due and the port. We reply with the scope, the mobilisation plan and a quote for that vessel.

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