What Is The Difference Between Active And Passive Heave Compensation?
Passive and active heave compensation compared side by side, with adaptive passive as the middle ground, and guidance on which approach suits which lift.
By Tord Martinsen & Peter Wang · · Reviewed · 7 min read
Practical application: most lifts land between the two architectures: compare ANTARES Adaptive PHC and RIGEL Basic PHC.
Choosing between active and passive heave compensation is one of the most important decisions in offshore lifting system design. Both approaches reduce the effect of vessel heave on a suspended load, but they differ fundamentally in how they achieve it — and in their cost, complexity, and suitability for different operations.
Passive Heave Compensation: Simplicity and Reliability
Passive heave compensation (PHC) uses a gas spring , typically a nitrogen-charged accumulator acting on a hydraulic cylinder, to create a compliant link between the crane and the load. The system absorbs vessel heave motion through the compression and expansion of gas, with hydraulic damping to control dynamics.
PHC requires no external power during operation, has no sensors or control system, and has very few moving parts. This makes it inherently reliable and well-suited to harsh offshore environments. Compensation performance is design- and case-specific: it depends on which input and output motion you measure, the payload, the excitation, the stroke and the tuning.
Norwegian Dynamics ANTARES takes passive compensation further by automatically adjusting its gas spring characteristics, achieving consistently high efficiency across varying conditions — without the complexity of a fully active system.
Active Heave Compensation: Maximum Performance
Active heave compensation (AHC) uses motion sensors, a real-time control system, and powered hydraulic actuators to actively drive the compensator in opposition to the measured heave. The achieved residual motion is case-specific, and a percentage only means something together with the metric, the excitation, the payload and the control limits it was measured under.
The trade-off is significant: AHC needs sensing, real-time control and powered actuation. Depending on architecture that actuation is hydraulic or electric — an HPU and an external supply are not universal; VEGA, ND’s active unit in development, is battery-powered with no umbilical. Installed power reaches the hundreds of kilowatts where the actuators have to drive the whole payload against the heave. An inline architecture that leaves a gas spring carrying the static load draws far less at the actuator, which is why the worked example on the active HC page lands an order of magnitude lower: any kilowatt figure needs its architecture, payload and duty stated before it can be compared with another. This adds weight, cost, and maintenance complexity.
Inline active heave compensators are available in both topside and subsea configurations, for the applications where maximum compensation performance is genuinely required.
Key Differences at a Glance
The choice is less about which architecture performs better and more about how much complexity a given lift has to carry. Passive buys reliability and independence from deck power, and gives up a few points of compensation efficiency for it. Active buys those points back, and pays for them in installed power, sensors, software and every failure mode that comes with them. The table below sets both against the adaptive middle ground on the criteria that usually decide it.
When to Use Which
For the majority of offshore lifting and subsea installation tasks, passive heave compensation provides sufficient performance at a fraction of the cost and complexity. This is particularly true when using an adaptive PHC system that can tune itself to changing conditions.
Active heave compensation is justified when:
- The operation demands very high positioning accuracy (e.g., J-tube pull-in, connector mating).
- Load weight varies significantly during the operation and cannot be predicted in advance.
- Environmental conditions are severe enough that passive efficiency is insufficient.
In many cases, the most cost-effective solution is a combination: an adaptive passive system like ANTARES for the majority of operations, with an active system reserved for the most demanding tasks. For a detailed comparison framework, see our heave compensator selection guide.
Choosing between passive and active compensation?
Choosing between AHC and PHC depends on accuracy, sea state, payload sensitivity and power. Send your lift case and we'll come back with the right architecture.
