CCS Certification vs DNV vs ABS: Hydraulic Winch Load Testing Protocol Differences for Offshore Vessel Retrofit Projects

A Flagup 150 kN marine hydraulic winch with CCS certification, designed for commercial vessel deck operations and offshore retrofit installations.

The classification landscape: three societies, three philosophies

When an offshore vessel operator decides to retrofit a hydraulic winch onto an existing deck, the classification society holding that vessel’s class notation dictates our testing protocol. In our daily engineering work at Flagup Hydraulic, we work with three societies dominate the conversation for retrofitted deck machinery: China Classification Society (CCS), DNV, and the American Bureau of Shipping (ABS). Each brings a different philosophy to the same question: proving winch performance under real loads.

In our experience across all three societies, CCS grounds its requirements in Chinese maritime industry standards, particularly CB/T 3689 for marine winch testing, and tends to work closely with domestic manufacturers who hold CCS factory approval. DNV, from which we have received numerous project approvals, operates from its Rules for Classification of Ships (Part 4, Chapter 6), takes a performance-based approach where the designer must demonstrate fitness-for-purpose through calculation and test. ABS, which we work with on North American and Middle Eastern projects, is guided by its Rules for Building and Classing Steel Vessels, splits the difference with prescriptive requirements layered onto a framework that allows equivalent solutions when justified.

For us as a hydraulic winch manufacturer, the practical consequence is that a single hydraulic winch model may need to undergo three different test sequences depending on which society classed the vessel it is being installed on. Our CCS-certified marine winch solutions are designed to meet all three frameworks.

Static overload testing: where the three protocols converge

Across all three classification societies, the foundation of hydraulic winch load testing is the static overload test. The requirement is straightforward in principle: apply a load equal to a defined multiple of our winch’s Safe Working Load (SWL) and hold it for a specified duration while monitoring for permanent deformation, leakage, and structural integrity.

The convergence on the 1.25× factor is no accident; it traces back to IACS Unified Requirements. However, the details diverge in ways that matter on test day. In our CCS experience, CCS places particular emphasis on gear tooth contact pattern verification after the overload test, a requirement we have not seen DNV or ABS inspectors request independently. DNV, in the projects we have supported, insists on documenting residual deflection numerically against a calculated allowable, turning our test into a data-recording exercise as much as a pass/fail event. ABS stands alone in requiring our brake to hold at 1.5× SWL as a separate static hold test, demanding a higher-capacity brake design.

Dynamic cycle testing: where they diverge

Static overload testing proves our winch can survive a peak load. Dynamic cycle testing proves it can survive thousands of real-world load cycles without fatigue failure. This is where the three classification societies show their strongest disagreements.

CCS typically requires, as we have verified in our CCS factory tests, a dynamic test of at least 100 load cycles at the SWL, with the winch operating through its full drum capacity (minimum rope pay-out and retrieval). The test is performed at rated hydraulic pressure and flow, and the inspector verifies that our drum brake engages and releases cleanly across all cycles. For winches rated above 50 kN, CCS may request an additional 20 cycles at 1.1× SWL as a margin verification.

DNV demands more for high-utilization installations: 200 cycles at SWL plus 50 at 1.1×, with pressure monitoring capped at 110% of rated working pressure. We have seen DNV halt a test on a spike CCS or ABS would accept.

ABS, based on our test records, requires 100 cycles at SWL, aligning with CCS on cycle count, but adds a requirement for a post-dynamic teardown inspection on critical winch components (gearbox, brake disc, drum bearings) when the winch is rated above a certain SWL threshold. This teardown is not a full disassembly; it is a visual and dimensional inspection of wear surfaces, documented in our test report. We have found the teardown requirement can add a full day to our test schedule, which retrofits on tight timelines need to account for.

Deflection measurement and acceptance criteria

In our CCS factory tests, how much a winch drum and frame deflect under load tells the surveyor whether the structural design is adequate. All three societies measure deflection, but they define acceptance differently.

We measure deflection using dial gauges in our CCS factory tests. CCS uses a 0.5% of span criterion for permanent set, measured with a dial gauge. Binary pass/fail.

DNV requires a calculated allowable deflection submitted before the test. If measured deflection exceeds 80% of allowable, an engineering assessment is triggered.

ABS specifies a maximum allowable deflection table by SWL range. If the deflection falls within the table, the test passes. For winches outside the table, ABS uses a calculated-allowable approach similar to DNV.

Documentation and certification packages

We manage documentation for all three societies, and our paperwork differences are where we encounter the most confusion from operators managing multi-class retrofits.

From our certification experience, our CCS documentation package includes: (a) a Chinese-language test certificate issued by the CCS-approved testing facility, (b) an English translation of the same certificate, (c) our winch General Arrangement drawing stamped by CCS, (d) material certificates for all load-bearing components (drum, shaft, gears), and (e) the hydraulic schematic with component specifications. CCS also requires the manufacturer to hold a CCS Factory Recognition certificate, which we maintain at our 20,000 m² facility through regular audits.

DNV documentation package includes: (a) a Design Verification basis, (b) Type Approval if applicable, (c) test reports, (d) a Maintenance Manual, and (e) material certificates from DNV-approved mills. DNV’s emphasis on our Design Verification basis means that the winch supplier must be prepared to explain why the design is the way it is, not just that it passed the test. The IMO Safety framework underpins all classification society rules, as outlined by the IMO Safety of Life at Sea (SOLAS) regulations. For detailed DNV requirements, the DNV Rules for Classification of Ships, Part 4 Chapter 6 provides the full framework.

For ABS-classed projects, refer to the American Bureau of Shipping rules portal for the latest requirements. ABS documentation package includes: (a) a Manufacturing Record Book (MRB), (b) signed test reports, (c) material certificates from approved mills, (d) a product description, and (e) the hydraulic schematic. ABS’s MRB is the most burdensome of the three, requiring documentation of the full production process.

Multi-class retrofit strategy: satisfying the strictest requirement

We frequently encounter vessels operating under one classification society but being retrofitted where a different society holds authority, or vessels transferring class notation mid-life. Our strategy is to design our test protocol around the most stringent requirement among all applicable societies.

In a typical multi-class project we handle, where the vessel holds CCS notation but is being dry-docked at a DNV-supervised facility, the combined protocol would include: (a) the DNV static overload test at 1.25× SWL with calculated allowable deflection documentation, (b) the DNV dynamic cycle count of 200 cycles at SWL plus 50 at 1.1× SWL, (c) the CCS gear tooth contact pattern verification after overload, (d) both Chinese and English test certificates, and (e) the CCS-stamped General Arrangement drawing. This adds roughly half a day but eliminates re-test risk.

Industry best practices for offshore equipment certification are also guided by the International Marine Contractors Association (IMCA) guidelines. For ABS-to-CCS transfers, our ABS MRB must be completed first, followed by our CCS package. We recommend starting the MRB 30 days before the test, because material traceability for load-bearing components often requires back-tracking to original mill certificates.

Factory witness testing vs. on-board acceptance

Factory or on-board: this is one of the first decisions in a winch retrofit, and each path has trade-offs in schedule, cost, and inspection scope.

Factory witness testing is, in our experience, the preferred path for CCS, which maintains a network of approved testing facilities in China. The CCS surveyor witnesses the full test and issues our certificate on-site. The winch then ships to the vessel with pre-completed documentation, and the on-board acceptance becomes a verification exercise rather than a full re-test. This works well for our CCS winch range because our CCS-approved Ningbo facility holds CCS factory approval.

DNV and ABS prefer on-board testing but accept factory certificates as partial credit. A full on-board test of a 15-ton winch needs certified loads and 4-6 hours; a verification test takes 1-2 hours.

First-retrofit mistakes that delay classification approval

here are the errors we see most often:

Starting the test without our approved drawing set

All three require approved GA drawings before the test. CCS needs the stamped GA; DNV rejects mismatched revisions; ABS holds the MRB open. We coordinate with CCS Marine Business services for factory recognition renewals. We provide stamped drawing packages with every CCS-certified winch, and we coordinate with DNV and ABS drawing approval on behalf of our customers during our order process.

Underestimating the brake test requirements

The brake is the most frequently failed component during load testing, usually due to test setup rather than undersized design. ABS’s 1.5× SWL static brake hold test requires that our hydraulic system be fully pressurized and then isolated, with the brake holding the load for the full 5-minute hold time. If the isolation valve leaks, the brake drifts and the test fails. We recommend a dedicated zero-leakage isolation valve rather than our recommended manifold.

Ignoring our documentation timeline

The test may take half a day, but documentation takes weeks. CCS certificates need translation; DNV Design Verification bases need engineering review; ABS MRBs need retrospective traceability. Start our documentation package when the order is placed.

A practical decision matrix for your next winch retrofit

The table below summarizes the key decision points. Contact our technical team for site-specific guidance.

At Flagup Hydraulic, we design our winch packages with multi-class certification in mind. Our 20-person R&D team organizes into specialized centers covering winch design, hydraulic systems, and electronic controls, we use to configure winch packages for any of the three classification societies from a single product platform. Our FJ series winches ship with CCS certification as standard, and we adapt DNV and ABS test protocols as project-specific packages.

The FJ17-45.60-140-18 hydraulic winch with CCS certification and A2FE axial piston motor, rated for 6-ton offshore vessel deck operations.