Hull Structural Integrity · Algeciras, Spain
Structural Condition of Ships Working the Strait: Cracks, Corrosion and Deformation at Algeciras
Ships that work the Strait of Gibraltar are loaded, flexed and turned round quickly, and their steel shows it in particular places. Open-deck container ships develop fatigue cracks at hatch corners, ro-pax ferries wear ramps, hinges and car decks on a repeated rotation, and tankers and car carriers corrode where coatings have failed. We mobilise a team from India to the ship at an Algeciras berth or at anchor, record where the steel has wasted or cracked, and report it in a form your technical department can assess against the ship's rules.
Open-deck ships and hatch corners
Large container ships rely on a wide-open deck for strength, and the corners of hatch openings carry high stress. Berth calls in Algeciras give a window to examine coaming corners and adjacent plating, clean them and test for cracks.
Ro-pax wear in one rotation
Ferries on the Tanger Med, Tangier, Ceuta and Tarifa crossings load vehicles every few hours. Ramps, hinges, car-deck plating and drain areas are examined and gauged during lay-overs and the off-season maintenance period.
Findings tied to the trade
A tanker discharging at San Roque and a car carrier relaying cargo corrode in different places. The report records pattern and location for each, so the superintendent sees where a ship of this type is likely to need steel next.
What does Strait trading do to a ship's structure?
Structural wear follows the way a ship is used, and the Algeciras trades are unusually varied. Mainline container ships pass through on long loops and relay boxes at the terminals, loading and discharging in quick rotation that changes the weight distribution along the hull from one call to the next. Feeders crossing between Iberian, North African and Atlantic ports repeat shorter cycles. Tankers bound for the San Roque refinery load and discharge in sequence, and ro-pax ferries make several crossings a day for most of the year.
Each of these produces its own pattern. Frequent load changes work the connections between longitudinal stiffeners and transverse frames. Salt spray and wet cargo handling attack deck plating and the underside of hatch covers. Ballast water exchanges expose tank boundaries to cycles of wetting and drying. A structural integrity inspection starts from the trade, because the places that matter on a feeder are not the places that matter on a refinery tanker.
Where do container ships crack and corrode at Algeciras?
Open-deck container ships carry torsional and bending loads through a hull with very large hatch openings. The stress concentrates at the corners of those openings, at the ends of hatch coamings and at transitions where the deck plating changes thickness. Fatigue cracks, when they start, usually begin at weld toes or at the edges of cut-outs in these areas, and grow slowly over many voyages. Cell guides, lashing bridges and hatch cover supports add further details that can crack or wear.
During a berth call, deck structure and the spaces beneath it can be examined while the cranes work, provided the area is cleaned and permitted. Cracks are looked for first by close visual inspection, then confirmed by magnetic particle testing, or penetrant testing where magnetic methods are impractical. Thickness readings on the plating around each detail show whether wastage is adding to the stress. Because relay calls are short, scoping is agreed with the chief engineer before arrival, and the list of details to be cleaned is ready when the team boards.
What gets inspected on ro-pax ferries and car carriers?
Ro-pax ferries and car carriers are inspected differently from cargo ships because their structure is full of decks, ramps and openings. The heavy rolling loads on ramps and car-deck plating produce wear and fatigue at hinge supports, ramp stiffeners and the connections to the shell. Drainage points collect water and salt, so plating near scuppers and in way of the bow and stern doors corrodes first. Ballast tanks under the car decks wear in the usual way, but their boundaries are often coated with little maintenance between dockings.
Lay-overs at Algeciras and Tarifa, and the quiet months outside the summer Operación Paso del Estrecho, offer windows for this work. The inspection covers ramp and hinge structure, car-deck plating by zone, door seatings and coamings, and accessible ballast tanks. Where a crack indication is found, its length and location are recorded with photographs and sketches, and a repair decision is left to the owner and class. For a ferry that cannot leave its schedule, we plan the sequence so the most important structure is examined first.
How are tankers at the San Roque berths examined?
Tankers calling for the refinery bring a different set of questions. Cargo tanks can only be entered when the ship is gas-free, so structural work at the berth normally concentrates on deck structure, pump rooms and segregated ballast tanks. Deck longitudinals, the plating beneath cargo pipelines and the areas around mooring fittings tend to show localised wastage. In ballast tanks, the usual suspects are underdeck structure and the lower strakes where coating breakdown allows grooving along weld lines.
Permit-to-work rules at the berth decide what is allowed and when, so the plan is built around the terminal's requirements and the ship's discharge programme. For an older tanker, the structural findings feed into the renewal survey planning, and they can also support a charterer's request for a condition assessment. The report distinguishes between general wastage, pitting and grooving, since the three have different consequences for the allowable margin.
How are buckling, set-in plating and damage recorded?
Corrosion is not the only way steel loses strength. Berthing contacts, tug pushing and cargo handling can leave dents, set-in shell plating and buckled stiffeners, particularly on ro-pax ferries and car carriers that berth many times a week. Panels that have buckled under compressive load also lose capacity, even where thickness readings are good.
Each deformed panel is recorded by location, extent and depth, with photographs and a sketch, and gauged around its edges to check for wastage. The superintendent receives a map of deformation that can be compared with the previous survey, so growth is visible. Where class has already recorded a deformation, we measure it again against the earlier figure instead of treating it as new.
How is a structural inspection planned around the bay's short calls?
Time in the bay is controlled by cargo, bunkering and berth windows, not by the inspection. We therefore ask for the ship's expected arrival, berth and sailing times as early as the agent can provide them, and build a priority list: details most likely to be cracked, members closest to the renewal limit, and spaces flagged during the last survey. Anything left over is rolled into a later port call or a docking.
Access arrangements are agreed in advance. The agent requests terminal passes and, for ships at anchor, a launch; the ship prepares cleaning at the details to be tested, lighting and gas-free certificates. A strong easterly in the Strait can delay boarding or cut an anchorage stay short, so jobs at anchor carry some float. When the findings justify a larger programme, the same team can continue at a nearby drydock without breaking the record.
Where hull structural integrity sits in the survey cycle
Every renewal survey asks for more thickness measurement than the last, and for oil tankers, chemical tankers and bulk carriers the ESP Code adds close-up survey on top. The table is the usual shape of the work; the class rules and the surveyor set the exact extent, which is why the measurement plan for a job at Algeciras is agreed in writing before mobilisation.
| 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 Algeciras
A gauging job at Algeciras runs the same way whatever the ship type. The sequence below is what the superintendent, the attending surveyor and the yard can expect from us.
- 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
Atlantis mobilises its inspection team from India to the vessel, for each job. There is no office or agent at the port; the team travels to the ship, which is why the planning step comes first. Work is planned and supervised by our Responsible NDT Level III, the founder, who holds ASNT NDT Level III in UT, RT, MT, PT and VT and has more than eleven years of international field experience. Technicians are qualified and certified under the company's written practice to ASNT SNT-TC-1A, and Atlantis is certified to ISO 9001 and ISO 14001.
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
- IACS UR Z7 for hull classification surveys
- IACS UR Z10.1 and Z10.4 for the enhanced survey of oil tankers and bulk carriers
- IACS Common Structural Rules for bulk carriers and oil tankers
- SOLAS chapter II-1 on structural strength and watertight integrity
- ASTM E709 and ISO 17638 for magnetic particle testing
- ASTM E797 for manual ultrasonic thickness measurement
What you receive
- Thickness readings by member with original thickness, diminution and allowable margin
- Crack indication sketches, lengths and photographs from magnetic particle or penetrant testing
- Hatch coaming and corner records for open-deck ships
- Ramp, hinge and car-deck condition records for ro-pax ferries and car carriers
- Deformation map with location, extent and depth of set-in or buckled panels
- Corrosion pattern records separating general wastage, pitting and grooving
Industries served
- Open-deck container ships
- Container feeders
- Ro-pax ferries on the Strait crossings
- Car carriers (PCTC)
- Crude and product tankers
- Bulk carriers waiting in the bay
- Chemical tankers
Frequently asked questions
Can hatch corner cracks on a container ship be found during a call at Algeciras?
Often yes, if the area can be cleaned and permitted while cargo work continues. Cracks are found by close visual examination, then confirmed by magnetic particle or penetrant testing. Because calls are short, the details to be tested are agreed with the chief engineer before arrival, so the team spends its time testing rather than searching.
Is a hull structural integrity inspection the same as a class survey?
No. It is an owner's inspection that measures steel condition, records corrosion pattern, deformation and cracking, and reports measured data your technical department or class engineer can assess. Our records are owner's NDT records, not class approvals. They are most useful when taken ahead of a survey, so the repair scope is known before the yard quotes.
What can be inspected on a ro-pax ferry during a lay-over at Algeciras or Tarifa?
Ramp and hinge structure, car-deck plating, door seatings and coamings, and ballast tanks that can be entered safely. Lay-overs are short, so we agree a priority list in advance. Crack indications at hinge supports and ramp stiffeners are tested by magnetic particle methods, and surrounding plating is gauged for wastage.
Can ultrasonic gauging find fatigue cracks in a ship's structure?
Not reliably. A thickness gauge measures the plate under the probe, and a fatigue crack at a weld toe is a surface-breaking defect that a thickness reading usually misses. We plan crack detection as its own task at known fatigue details, using close visual inspection and magnetic particle or penetrant testing after cleaning, and use gauging to check the plating around each detail.
What happens if a tanker at San Roque needs structural work beyond what the berth allows?
We record what can be reached at the berth, usually deck structure, pump rooms and segregated ballast tanks, and list the spaces that need a gas-free window or a dock. The report gives the superintendent a ranked list, so cargo tank gauging or repair planning can be programmed into the next suitable stay.
How does a team reach a ship at anchor in Algeciras Bay?
The ship's agent books a launch and arranges access, and the technicians board with their equipment. Boarding depends on weather, particularly strong easterly winds in the Strait, so we keep some margin in the plan. Tanks to be entered must be certified safe, and cleaning at crack-test locations should be done before the team arrives.
Can hull structural integrity at Algeciras be credited to a class survey?
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.
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.
Request a QuoteRequest 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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