DNV-ST-N001 (replaced OS-H205, OS-H101): Marine Operations

DNV-ST-N001 is the technical standard governing the planning, execution and warranty of marine operations: offshore lifts, transports, towing, mating, loadout and decommissioning. Issued in 2020, it consolidated several legacy DNV-OS-H series standards into a single document. For offshore lifting work, ST-N001 is the document that sets dynamic load factors, environmental criteria, alpha factors and the operational reference periods that drive every lift procedure.

Practical application: For practical application of this topic, see engineering studies and analysis and product / system design.

In this article

What ST-N001 covers

ST-N001 is structured around seven main parts:

  • General principles for marine operations
  • Environmental conditions and limit criteria
  • Design factors and methodology
  • Lifting operations (Section 5 — most relevant to compensator users)
  • Transports
  • Loadout, mating, demating
  • Other marine operations (decommissioning, hookup, abandonment)

The standard applies to marine operations executed offshore. Operations during transit between ports, dockside and inland operations are covered by other rules.

The 2020 consolidation: OS-H101, OS-H205, OS-H206

Before ST-N001, marine operations were governed by separate DNV Offshore Standards (OS) documents:

  • DNV-OS-H101 — Marine operations, general
  • DNV-OS-H102 — Marine operations during loadout
  • DNV-OS-H103 — Modelling and analysis of marine operations (now DNV-RP-N103)
  • DNV-OS-H201 — Load transfer operations
  • DNV-OS-H202 — Sea transports
  • DNV-OS-H203 — Transit and positioning
  • DNV-OS-H204 — Offshore installation
  • DNV-OS-H205 — Lifting operations
  • DNV-OS-H206 — Loadout

In 2020 DNV reorganised these into ST-N001 (consolidated requirements) plus RP-N103 (modelling and analysis) and RP-N202 (lifting recommendations). Operators frequently still reference the legacy designations — when you see “DNV-OS-H205” in a procedure, the technical content lives in ST-N001 Section 5.

Section 5 — Lifting operations

ST-N001 Section 5 covers the lifting operation itself:

  • Lift planning (vessel positioning, route, weather strategy)
  • Crane and rigging selection
  • Rigging arrangement — including any heave compensator or shock absorber
  • Sling and shackle calculations
  • Pad-eye and lift-point design verification
  • Calculation of design loads on the crane and the structure being lifted
  • Operational procedures and pre-lift checks
  • Documentation and warranty surveyor approval

Section 5 includes specific clauses on DAF calculation, snap-load assessment, friction factors, and the requirement to maintain crane SWL margin under combined static and dynamic loads.

Dynamic load factors and the 1.3 floor

Section 5 sets minimum DAF values regardless of analysis. For offshore lifts:

  • Bare hook with no hydrodynamic-significant payload: typically DAF ≥ 1.10
  • Subsea lifts with payload below the splash zone: typically DAF ≥ 1.30
  • Lifts at the splash zone or with payload partly above water: typically DAF higher, calculated case by case

The 1.30 floor for subsea lifts captures residual uncertainty in dynamic analysis and the practical reality that calculated DAF rarely matches measured DAF perfectly. A heave compensator that measurably reduces DAF below 1.30 still doesn’t allow procedurally claiming lower than 1.30 — the floor is procedural.

For a deeper treatment of how DAF is calculated, see Dynamic Amplification Factor (DAF). For the implications on crane capacity, see Crane Load Chart.

Alpha factors and weather forecasting

Marine operations cannot rely on the forecast wave height being exactly right. ST-N001 implements an alpha-factor approach:

  • For an operation expected to take Top hours, the procedure requires a forecast covering at least 3 × Top hours
  • The forecast wave height is multiplied by an alpha factor (typically 0.7–0.85) to account for forecast uncertainty
  • The lift can only proceed if the alpha-corrected forecast remains within the operational Hs limit for the entire reference period

This means a 4-hour lift requires 12 hours of forecast where the alpha-adjusted Hs remains within the limit — a substantial weather-window requirement.

A heave compensator that widens the Hs limit also makes alpha-factor compliance easier, because both the absolute limit and the forecast headroom become larger. See Weather Windows for Offshore Lifting for the economic effect.

Marine warranty surveyor role

Most insured offshore projects appoint a Marine Warranty Surveyor (MWS) — an independent engineering consultancy responsible for approving lift procedures and witnessing critical operations. The MWS works to ST-N001 plus client-specific addenda.

Typical MWS approval scope:

  • Lift procedure (calculations and operational steps)
  • Crane and rigging certification
  • Heave compensator certification (if used)
  • Vessel suitability and crane class
  • Weather strategy and decision criteria

Compensator manufacturers like Norwegian Dynamics issue certification documentation in formats that match MWS approval expectations — saving project time and avoiding rework.

ST-N001 in heave compensation procurement

For a project specifying offshore lifting equipment, ST-N001 typically appears in the technical specification alongside DNV-ST-0378 (the appliance standard):

  • Equipment is certified to ST-0378
  • Operations are planned to ST-N001
  • The vendor’s calculation package includes ST-N001-compliant DAF values, environmental limits and alpha factors

Norwegian Dynamics products are designed and certified to ST-0378 with calculation packages aligned to ST-N001 procedures.

Related on Norwegian Dynamics

Working on a lift that needs this?

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