CAP Thickness Measurement · Vlissingen, Netherlands

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

A Condition Assessment Programme asks an older tanker or bulk carrier to prove its steel is sound, and the thickness data behind that proof has to be gathered somewhere the ship can be opened up. In Zeeland the opportunities are the Sloe area jetties, the dry bulk quays and the repair yard at Vlissingen-Oost. Atlantis NDT sends a team from India to the ship to gather pre-CAP and CAP gauging in the order the cargo operation, the gas-free certificate and the society's CAP team allow, and delivers the readings in a form the society's engineers can use.

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Gauging in the cargo window

Chemical and product tankers at the Sloe jetties stay for the length of the cargo operation. Piping and deck readings fit that window, while tank gauging waits for a gas-free stop, so a CAP plan here is built from several short opportunities rather than one long one.

Bulk carriers once the holds are clear

After discharge at the dry bulk quays, hold frames, tank tops and hatch coamings can be reached while the holds are empty. A CAP survey for a bulk carrier uses that stop, before the next cargo is loaded and the surfaces are covered again.

Know the result before the society attends

Pre-CAP gauging of the critical areas shows the owner whether the ship is likely to reach the rating that charterers want. The owner then decides on steel renewal at the yard first, instead of finding out during the society's survey.

Where does CAP gauging fit at Vlissingen and Terneuzen?

CAP gauging does not need a dock for most of its work, which makes the Sloe area useful. A tanker alongside a chemical or oil jetty can have deck structure, cargo and ballast piping and manifold areas gauged under the terminal's permit to work. Tank interiors are different: they need to be gas-free and ventilated, and a terminal will rarely allow tank entry during cargo operations, so interiors wait for a cleaning stop.

The repair yard at Vlissingen-Oost is where the interiors are normally finished. A tanker or bulk carrier that is already gas-free for yard work can have the tank programme completed there in a few days. Across the estuary at Terneuzen, chemical tankers use their own jetties, and one mobilisation can cover a ship in each place if the agent sequences the visits and the ships share a window.

Sloe area jetties: deck, manifold and cargo piping readings during cargo operations.
Dry bulk quays: hold frames, tank tops and hatch coamings after discharge.
Damen Shiprepair Vlissingen: tank interiors and close-up survey support when the ship is gas-free.
Terneuzen jetties: piping and deck structure on chemical tankers, in the same mobilisation.

Which ships at Vlissingen are asked for a CAP rating, and why?

Charterers' vetting teams ask older tankers and bulk carriers to show the condition of their steel, and the ships serving the chemical and fuel industry around the Westerschelde are no exception. Product and chemical tankers that load at the Sloe or at Terneuzen are often mid-life or older, and the cargo owners they serve want evidence beyond the year of build. A bulk carrier carrying agribulk or steel products through North Sea Port faces a similar question from its charterers.

Owners with several older ships use the rating to keep them trading with the same customers. For them, a CAP survey is a business decision about the steel they will renew and the steel they will not. Our part in that decision is the thickness data, with the survey, the close-up examination and the rating itself remaining with the classification society.

How is CAP gauging scoped for tankers and bulk carriers at this port?

The society's CAP team sets the minimum extent, and for older ships that extent is larger than a normal renewal survey. We start from the CAP procedure of the society concerned, the previous TM reports and the drawings, and agree the extent with the owner and the society before travelling. Critical structure comes first: the cargo tank boundaries, the ballast tank bottoms and the transverse sections that feed the strength assessment on a tanker, and the cargo hold frames and tank top on a bulk carrier.

For a chemical tanker with stainless steel or coated tanks, the question is which tanks carry carbon steel boundaries that waste in the usual way. We note that early, because it changes which tanks carry the weight of the programme. Where coating is intact, the readings are taken through it only with equipment verified for the purpose, so we do not strip good coating off just to gauge steel.

What does CAP gauging typically find on ships in the Zeeland trades?

On product and chemical tankers, we find wastage on the ballast tank boundaries, where heated cargo against cold ballast water accelerates corrosion, and on deck plating near the manifolds where cargo spillage and wash accumulate. On bulk carriers carrying coal, steel or agribulk, hold frames lose steel at the lower ends, where cargo abrasion and moisture work together, and tank tops show localised pitting where cargo has lain wet.

Pitting and grooving at weld lines also matter more in CAP than in a routine survey, because the society looks at their depth and extent when it sets the rating. We record these separately from general plate thickness. If the pre-CAP data shows a ship close to the limit in a few areas, the owner can renew those plates at the yard, then request the CAP survey knowing where the steel stands.

How is a CAP gauging job planned around a Vlissingen call?

The planning problem is sequence, because the society, the cargo operation and the yard all have their own timing. We ask the owner for the society's CAP requirements, the vessel's schedule and the tank cleaning plan, and propose an order of work that puts piping and deck readings in the cargo stop and the tank interiors in the cleaning stop.

Visa and travel times for a team from India mean the schedule must reach us early. The agent arranges gate passes at the Sloe jetties or at the yard and any launch for work at the anchorage. If the society's surveyor is attending, we agree the programme with them beforehand so that the data is organised the way their engineers will use it, and no gauging has to be repeated during their survey.

Society, CAP scope and the survey date requested.
Cargo schedule and the planned tank cleaning stops.
Previous TM reports and any steel renewed since.
Which tanks carry carbon steel boundaries and which are coated.

Where cap thickness measurement sits in the survey cycle

How much steel has to be gauged depends on which survey the ship is due for, its type and its age. The pattern below is the usual one under IACS unified requirements; the attending surveyor and the class rules for the ship decide the final extent. For a ship calling at Vlissingen, we agree the programme with the class and the owner before the team mobilises.

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 Vlissingen

The sequence for a thickness measurement job at Vlissingen 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

Classification society CAP procedures (each society publishes its own scheme)
IACS UR Z10.1 and Z10.4 – Hull surveys of oil tankers and double-hull oil tankers
IACS UR Z10.2 and Z10.5 – Hull surveys of bulk carriers and double-skin bulk carriers
IACS UR Z10.3 – Hull surveys of chemical tankers
IACS Common Structural Rules for oil tankers and bulk carriers
ASNT SNT-TC-1A – Personnel qualification and certification in NDT

What you receive

Thickness readings organised by the society's required forms and by frame and strake
Pre-CAP summary showing areas close to the allowable limit and the steel renewal they imply
Pitting and grooving records with depth, extent and location
Separate record of readings from piping and deck structure taken at the Sloe jetties
Numbered sketches locating each reading for the society's strength assessment
List of tanks and holds not gauged, with the reason for each

Industries served

Chemical tankers loading at the Sloe and Terneuzen
Product tankers on North Sea Port trades
Double-hull crude and product tankers
Bulk carriers carrying coal, steel products and agribulk
General cargo ships with older steel
Heavy-lift and project cargo ships
Older ships traded by owners with several vessels

Frequently asked questions

Can CAP thickness gauging be done at a Sloe area jetty in Vlissingen?

Part of it can. Deck structure, manifold areas and cargo or ballast piping can be gauged under the terminal's permit during cargo operations. Tank interiors need a gas-free tank, and terminals rarely allow entry during cargo, so those wait for a tank-cleaning stop or the yard. We separate the two parts in the plan.

Does pre-CAP gauging replace the society's own survey?

No. The society carries out the survey and issues the rating. Pre-CAP gauging is the owner's own measurement, which shows where the steel stands before the society attends. It lets the owner renew plates first and request the survey with a clearer view of the likely result.

Which ships in Zeeland benefit most from a CAP rating?

Mid-life and older chemical and product tankers serving the industry around the Westerschelde, and older bulk carriers on North Sea Port trades, are typical. Charterers' vetting teams ask these ships for evidence beyond the year of build, and a rating can keep them trading with the same customers.

Can one team cover tankers at Vlissingen and Terneuzen in one trip?

Yes, when the agent can sequence the calls and the ships are available in the same days. The two ports are close, and the team moves between jetties. Each ship keeps its own gas-free and permit requirements, so the order of work is agreed ship by ship before we travel.

What does the society need from the thickness data?

The society's engineers need readings tied to the structure: frame, strake and longitudinal, on its own forms, with pitting and grooving recorded separately. Organised that way, the data goes straight into the strength assessment. Ask the society for its current CAP requirements before the plan is fixed.

Can cap thickness measurement at Vlissingen 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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