Dry-docking: the inspection and renewal cycle for Philippine inter-island vessels

A vessel's hull does not deteriorate uniformly or predictably. Corrosion, biological fouling, mechanical wear on the propeller and rudder, erosion at the sea chests, and stress fatigue in the hull plating accumulate invisibly below the waterline over years of operation. The only way to inspect and address this deterioration is to remove the vessel from the water entirely. Dry-docking is not a preference or a commercial decision. For Philippine-registered vessels, it is a mandatory legal requirement administered by the Maritime Industry Authority (MARINA) under Memorandum Circular No. 152,1 and operating a vessel past its scheduled dry-docking date without MARINA authorisation is grounds for suspension of the vessel's safety certificates.

For cargo shippers, dry-docking matters because it takes vessels off the water for periods of two to four weeks and affects fleet availability on specific routes. A reputable operator plans dry-docking schedules well in advance and communicates them to customers. An operator who cannot tell you when their vessels were last dry-docked, or whose vessels are running on extensions, is an operator whose maintenance status you should investigate before loading cargo.

MARINA MC 152 mandates that all Philippine-registered domestic vessels (excluding motorised bancas with outriggers) undergo dry-docking twice within every five-year cycle.1 For classed vessels — those enrolled with a classification society — the interval between successive dry-dockings is 24 months, with provision for a single extension of up to six months if an afloat underwater inspection supports the extension.1The practical rhythm for most of our vessels is a dry-docking approximately every two years, coordinated with the classification society's survey calendar.

MARINA Memorandum Circular No. 178 amended MC 152 to clarify that only shipyards holding a MARINA licence are authorised to conduct dry-docking work on Philippine-registered domestic vessels.2 A vessel cannot satisfy its dry-docking requirement by going into an unlicensed facility, regardless of the work actually performed there. All dry-dockings in our fleet are conducted at MARINA-licensed yards, with a MARINA surveyor present during the hull inspection.

In-water inspection with ultrasound thickness gauging (UTG) is permitted as an alternative to physical dry-docking for vessels under 10 years of age, subject to MARINA surveyor approval.1 We use in-water inspection where the survey results support it, but it does not replace the full dry-docking cycle. It can extend an interval; it cannot substitute for taking the vessel out of the water and examining the complete underwater body.

Once the vessel is in the dry dock and the water is pumped out, the MARINA surveyor and the shipyard team conduct a systematic inspection of the entire underwater body. This is the only point in the vessel's maintenance cycle where the full external hull surface is accessible for direct visual and physical examination.

1. 01Hull plating. Every plate in the bottom, side, and bilge sections is inspected visually and by ultrasound thickness gauging. The UTG measurement is compared against the original approved plating thickness minus the MARINA-approved wastage allowance.3 Plates that have corroded below the allowable wastage limit are renewed before the vessel is undocked. This is not optional — a vessel with hull plates below minimum thickness cannot receive a Certificate of Drydocking.
2. 02Propeller and shaft. The propeller blades are inspected for cavitation erosion, cracks, and pitch deformation. The shaft is withdrawn for inspection of the bearing surfaces, seals, and stern tube. Any deformation or wear beyond tolerance is repaired or the component renewed. A propeller running with blade damage or a shaft with worn bearings is both a performance and a structural safety issue.
3. 03Rudder. The rudder pintles and gudgeons — the hinge fittings that connect the rudder to the hull — are inspected for wear and corrosion. The rudder blade is gauged for plate thickness. The rudder stock seal is replaced if worn. Rudder bearing clearances are measured and compared to the approved tolerances specified in the Philippine Merchant Marine Rules and Regulations.3
4. 04Sea chests and hull fittings. Sea chests are the underwater openings through which seawater is drawn for cooling systems, firefighting, and ballasting. The gratings, valves, and plating around each sea chest are inspected and the grating cleaned of marine growth that has accumulated since the last dry-docking. Sea cock valves are tested for function and renewed if they cannot be operated cleanly.
5. 05Keel and keel blocks. The keel is inspected for deformation and the keel block points where the vessel rested during dry-docking are checked for stress marks or indentation that might indicate abnormal loading on the hull structure.

The UTG measurement is the number that matters most. A hull plate that looks sound from the outside may be wasted to failure thickness on the inside. You cannot know without gauging it.

The sequence in a dry-docking period follows a fixed order. The vessel enters the dock, is positioned on keel blocks, and the dock is dewatered. Once the hull is dry and clean, the inspection team carries out the surveys described above before any repair work begins. Repairs done before inspection are invisible to the surveyor — the survey sequence matters.

After the inspection and before undocking, the hull is cleaned of accumulated marine fouling by high-pressure water blasting. The underwater hull then receives a new coat of antifouling paint. The antifouling compound selected depends on the vessel's operating profile: vessels on slow inter-island routes with frequent port calls use a different antifouling specification than vessels on faster, longer ocean passages. Antifouling performance directly affects fuel consumption — a clean, well- coated hull at a given speed burns measurably less fuel than a fouled hull. The payback on antifouling investment shows up in the bunker bill over the subsequent 24 months.

Any repairs identified during inspection are completed before undocking. The shipyard submits a Drydocking Report to MARINA on the prescribed Annex A form within five working days of undocking.1 The report documents every item inspected, every measurement taken, every repair carried out, and the materials used. MARINA reviews the report and issues the Certificate of Drydocking upon confirmation that the work meets the required standards.

The Certificate of Drydocking is issued by the MARINA-licensed shipyard that conducted the work, following confirmation that the inspection and repairs satisfy the applicable MARINA requirements.1 It is vessel- specific, date-stamped, and tied to the next scheduled dry-docking date. A vessel operating without a current Certificate of Drydocking — one that has lapsed because the vessel missed its scheduled dry-docking — is not in compliance with MC 152 and may not operate until the situation is rectified.

The dry-docking occasion is also typically coordinated with the renewal of other safety certificates that fall due at approximately the same interval: the vessel's Safety Certificate, Load Line Certificate, and any classification certificates that require a periodic hull survey. Scheduling these renewals to coincide with the dry-docking minimises the number of times the vessel has to come out of service for compliance purposes.

We maintain a rolling dry-docking schedule for the entire fleet. Every vessel's last dry-docking date, its next scheduled date, and its certificate expiry are tracked against the MARINA MC 152 requirements and the classification society survey calendar. When a vessel's dry- docking window approaches, we notify customers on affected routes at least six weeks in advance, confirm the yard booking, and plan fleet coverage to minimise disruption to cargo commitments.

We do not defer dry-dockings to accommodate cargo bookings. The pressure to keep a vessel in service to fulfil a contract is real, but a vessel that misses its dry-docking date is an unregistered liability — operating outside its compliance window, with an underwater body that has not been inspected in more than 30 months. The risk that creates for the cargo on board, the crew, and our operating licence is not acceptable. When the dry-docking date comes, the vessel goes to the yard.