An offshore lift in a long regular swell at dusk, the payload hanging steady and plumb below a compensator in-line on the crane fall

Resonance avoidance

Uncompensated, a lift can find the sea’s own rhythm — the compensator moves the system clear of it.

Resonance Avoidance

Q: What is resonance in a heave compensation system?

The condition where the system's natural frequency — set by the suspended mass and the gas-spring stiffness — coincides with the dominant wave frequency. Instead of reducing motion, the system amplifies it: the load moves more than the crane tip.

Q: How bad can resonant amplification get?

An undamped system at resonance would theoretically respond infinitely; in practice damping caps it: for damping ratios around 0.10–0.25 the single-degree-of-freedom peak runs 2–5× (≈1/2ζ) — the opposite of what a compensator is for.

Q: When is resonance risk highest?

When the gas volume is too small (a stiffer spring shortens the natural period), when the load is lighter than the design case (same effect), or when long-period swell pushes the excitation period up toward the system's natural period.

Q: How do engineers design around resonance?

Sufficient gas volume to keep the natural period well above the wave periods, adequate damping as a safety margin, analysis across the full load range (the lightest load is usually the riskiest), and adaptive tuning — ANTARES adjusts its gas spring automatically to hold the optimal natural period as conditions change.

Q: Does resonance only concern the compensator itself?

No — crane wire, sheaves and subsea rigging each add stiffness and mass, creating coupled modes. In deep water the wire's elasticity is significant, and the coupled wire–compensator system resonates differently from either alone, which is why critical operations verify with time-domain simulation using site wave data and vessel RAOs.

By Tord Martinsen, CEO · March 2026 · Reviewed August 2026 · 6 min read

Practical application: moving the system period away from the waves is a selection problem: see ANTARES Adaptive PHC and engineering studies and analysis.

Resonance is first a property of the uncompensated crane–wire–payload system: it occurs when the excitation runs at a natural frequency of that system. Adding a compensator changes the coupled modes — the compensated system is then checked across the defined cases. The result is dramatic amplification of load motion, the opposite of what a compensator is supposed to achieve. Designing around resonance is one of the most critical aspects of compensator engineering.

What Is Resonance?

Every spring-mass system has a natural frequency — the frequency at which it tends to oscillate when disturbed. In a passive heave compensator, the mass is the suspended load and the spring is the compressed gas in the accumulator.

When the wave-driven crane tip motion oscillates at or near this natural frequency, the system responds with amplified motion — the load moves more than the crane tip rather than less. This amplification can be dramatic: an undamped system at resonance would theoretically have infinite response.

In practice, damping caps the peak response; how high the peak runs at resonance depends on the damping actually configured — which is why the screening model states its damping instead of quoting a universal factor. This is clearly unacceptable for a device designed to reduce motion.

Where Resonance Occurs

The natural period of a passive heave compensator depends on the load mass and the gas spring stiffness. For the Norwegian Dynamics unit set in the basis below, calculated natural periods span roughly 10–30 seconds; each project calculates its own coupled period from the actual mass, gas state and line stiffness.

On the North Sea screening basis used here, peak spectral periods of 5–15 seconds (Tp) are the indicative excitation band; the project site’s own metocean basis governs. For well-designed systems the natural period sits well above the energetic wave periods, so the excitation frequency stays above the natural frequency — the isolation region. The margin is verified against the project wave spectrum rather than assumed.

However, resonance risk increases when:

The gas volume is too small (making the spring too stiff and reducing the natural period).
The load is lighter than the design case (reducing the mass and thus the natural period).
Long-period swell is present (increasing the excitation period towards the natural period).

System natural period, dominant wave periods and amplification at resonance — typical ranges and the governing design rule.
Quantity	Typical range	The design rule
System natural period T_n	10 – 30 s	Keep T_n well above T_p — operate sub-resonance, where compensation works
Dominant wave periods T_p	5 – 15 s
Amplification at resonance	2 – 5× even well-damped	The zone the whole design exists to avoid

Gas volume too smallStiffer spring → shorter T_n

Lighter load than designLess mass → shorter T_n

Long-period swellExcitation climbs toward T_n

Three ways the margin erodes — and why the lightest expected load, not the design point, is usually the governing check.

Designing Around Resonance

Engineers use several strategies to ensure heave compensators operate safely away from resonance:

Sufficient gas volume — Larger gas volumes produce softer springs with longer natural periods, pushing the resonance well above the wave period range.
Adequate damping — Hydraulic damping limits the amplification at resonance to acceptable levels, providing a safety margin even if conditions push the system closer to its natural frequency.
Load range analysis — The compensator must be checked across the full range of expected loads, not just the design point. The lightest load typically gives the shortest natural period and therefore the highest resonance risk.
Adaptive tuning — ANTARES adjusts its gas-spring working point automatically as load conditions change, holding the natural period where the analysis put it. Each setting is still checked in the coupled model — adaptation widens the workable range, it does not remove the check.

Resonance in System Design

Resonance avoidance is not just about the compensator — it applies to the entire lifting system. The crane wire, sheaves, and any subsea rigging all have their own stiffness and mass, creating a coupled system with multiple potential resonance modes.

At greater water depths, the wire’s elasticity becomes significant, and the coupled wire-compensator system can have resonance frequencies different from either component alone. This is why deepwater operations require careful coupled dynamic analysis that models the entire system from vessel to seabed.

For critical operations, time-domain simulations with site-specific wave data and actual vessel RAOs verify the response across the defined operating cases. Norwegian Dynamics provides engineering support for these analyses as part of compensator selection and sizing — see our compensator selection guide for more information.

Resonance avoidance — frequently asked

What is resonance in a heave compensation system?

The system’s natural frequency — set by load mass and gas-spring stiffness — meeting the dominant wave frequency. The load then moves more than the crane tip, not less.

How bad can resonant amplification get?

Undamped: theoretically unbounded. Well-damped: for damping ratios around 0.10–0.25 the single-degree-of-freedom peak still runs 2–5× (≈1/2ζ) — unacceptable for a device meant to reduce motion.

When is resonance risk highest?

Small gas volume (stiff spring), a lighter-than-design load, or long-period swell — each pushes excitation and natural period toward each other.

How do engineers design around resonance?

Big enough gas volume (long T_n), adequate damping as the safety net, load-range analysis down to the lightest case, and adaptive tuning — ANTARES holds the optimal natural period as the load changes.

Does resonance only concern the compensator itself?

Wire, sheaves and rigging add their own stiffness and mass; in deep water the coupled wire–compensator modes differ from either component alone. Critical lifts verify with time-domain simulation on site wave data and vessel RAOs — part of a CONSTELLATION study.

Worried about resonance in your lift system?

Resonance is a tuning problem. Send your wave climate and crane stiffness and we'll show how a compensator shifts the natural period.

See it in action

Through resonance, in control — ANTARES takes a flooded suction pile through its resonance band near 1,300 m, simulated in CONSTELLATION.

ND SolutionANTARES →Adaptive passive heave compensator — tune away from resonance in real time.

DampingDamping is the primary tool for controlling resonance when it cannot be avoided.

Vessel MotionsVessel motion periods define the excitation frequencies that must not coincide with system natural frequencies.

WavesWave spectra determine the range of excitation frequencies present in the system.

Basis and assumptions

Where the figures on this page come from, and how far each one can be carried. Screening values are modelled estimates; they are not a substitute for a project-specific analysis on your own basis.

Compensator natural period 10–30 sDesign range (model output): Follows from the load mass and the gas-spring stiffness across the SWL and stroke bands Norwegian Dynamics builds. It is the range our own units fall in, not a property of heave compensators in general — the natural period of any specific unit is computed for that lift.
Dominant wave periods 5–15 sPublished source / standard: Typical North Sea peak-period range. Sea-state parameters and the spectra used to describe them are given in DNV-RP-C205, Environmental conditions and environmental loads.
Amplification 2–5× at resonanceDerivation: For a lightly damped single-degree-of-freedom system the steady-state amplification at resonance is approximately 1/(2ζ). A damping ratio ζ of 0.10 gives about 5× and ζ of 0.25 about 2×, which is the band quoted here. Real systems depart from this as soon as the damping becomes non-linear, which is why the operating case is modelled rather than read off a curve.