One passive unit, many operating points — retuned phase by phase, on battery.
Adaptive Passive Heave Compensation
How an adaptive passive compensator differs from a fixed-setting passive unit: what it changes between phases of a lift, what that solves, and when it is worth choosing over a basic PHC.
By Tord Martinsen & Peter Wang · · Reviewed · 5 min read
Adaptive passive heave compensation is an advanced form of passive heave compensation that can adjust its performance characteristics to suit different phases of an offshore lifting operation. Unlike basic PHC systems with fixed settings, adaptive compensators can switch between operating modes (such as locked, splash zone, and subsea) to optimize performance for each stage of the lift.
This makes adaptive PHC systems ideal for complex operations that involve multiple challenges, such as lifting through the splash zone followed by a precise subsea landing.
What's the difference between an adaptive PHC and a basic PHC?
Typically an adaptive PHC is a higher-cost, higher-performance compensator. The main differences are summarised in the table below:
| Feature | Basic PHC | Adaptive PHC |
|---|---|---|
| Cost | 1× | 2–3× |
| Gas to oil ratio | Sized once for the lift duty | Larger, with reserve gas for in-service retuning |
| Stroke equilibrium control | No | Yes |
| Adjustable stiffness during use | No | Yes |
| Adjustable damping during use | No | Yes |
| Quick lifting | No | Yes |
| Temperature compensation | No | Yes |
| Weight compensation | No | Yes |
| Depth compensation | No | Yes |
| Battery operation | No | Yes |
| Data logging | No | Yes |
| Rod locking | No | Yes |
What does the adaptive PHC solve?
What the adaptive unit adds is a set of operating modes. The load path stays passive in all of them; what changes is stiffness, damping and where the rod sits in its stroke.
Rod held for deck handling
The piston rod is locked so it cannot extend when the payload is picked up, which keeps the required lifting height down while the load is still over the deck.
Stiffer and better damped through the surface
Higher stiffness and higher damping in both directions, with the equilibrium position offset to allow for the buoyancy the load picks up as it enters the water.
Cooling and depth corrected on the way down
Seawater cools the unit and its gas pressure falls, so onboard high-pressure gas is injected to hold the pressure at the right level. As depth builds, external pressure pushes the rod inwards and gas pressure is adjusted down to match. Extremely deep water with light payloads needs a different technique again: contact us for that case.
Soft for landing and resonance avoidance
A larger gas volume is connected to the cylinder, lowering the spring rate. That cuts load variation over stroke at set-down — whether it also moves the system clear of a resonance concern is checked in the lift model, not assumed.
Controlled lift-off, repeatable
Tension is first held below the weight of the payload, then raised quickly so the rod retracts in a controlled way. The sequence can be run more than once, which matters when a lift-off has to clear on the first attempt.
Asymmetric damping for snap and overload
Extension damping is limited while retraction damping is raised, so the unit yields through its stroke on the event and controls the return. How much of the peak that removes is read off the event’s force–stroke response in the model.
Three capabilities run underneath all six rather than being modes themselves. Filling and preparation are software controlled, checked against the parameters of the lift being prepared. The unit weighs the payload once it is attached and corrects its gas pressures on the fly if the figure differs from plan, with no trip back to deck. And every lift is logged, so stroke usage, DAF and landing speeds can be read back afterwards.
All six modes are the same gas-spring hardware under different settings, applied on the fly and logged for review afterwards. The primary load path stays passive alongside the added capability; the adaptive functions add valves, sensors, controls and a battery, each with a defined safe state on loss. That operating envelope is what ANTARES was built around.
When should an adaptive PHC be used instead of a basic PHC?
- If a basic PHC cannot deliver the performance the operation needs, most often during landing.
- If the equilibrium position will drift too much with a basic PHC (can be offset partly by using longer stroke) for example due to buoyancy or water depth.
- When different settings are needed to achieve the target dynamics, for example one setting through the splash zone and another subsea.
Adaptive passive HC — frequently asked
What is adaptive passive heave compensation?
What is the difference between an adaptive and a basic PHC?
Does an adaptive PHC need external power?
What happens when the compensator cools down in seawater?
When is an adaptive PHC worth it over a basic one?
Need one unit to cover several lift modes?
ANTARES is our adaptive passive compensator — same hardware, multiple operating points. Tell us the lift data and we'll come back with sizing.
See it in action
ANTARES adaptive passive heave compensation — deck to seabed, simulated in CONSTELLATION
