Quick Lifting
Build clearance while the deck keeps moving.
The payload and the deck keep moving.
Quick lifting uses controlled compensator retraction to build separation. The required clearance must be maintained through the lift-off transient.
Separation is opening
A favourable relative-motion condition can help create separation. The trigger is defined for the coupled crane, load and deck motion.
The deck can close the gap
Initial lift-off alone is not enough. Following deck motion can reduce clearance while the payload is still close.
Concept sketches only: no time history, velocity scale or trigger setting is implied. The lift analysis establishes the transient clearance and load response.
Use the favourable point in relative motion defined by the lift procedure. Preload, available travel, retraction force and the operating envelope are set for the specific lift.
Read the result together with its assumptions.
Modelled re-contact frequency for the same 250 t payload and sea-state definition. The conventional rigid-line crane and ANTARES quick-lift cases use the stated favourable trigger condition.
modelled re-contact frequencyANTARES quick lift
re-contacts / trials
Bars use a common 0–100% scale. The speeds and reported frequencies are retained from the original case table; these are model outputs, not general operating limits.
The published case reports 0 of 120 realisations at each tested point, with a stated 95% interval of 0–3% for that model setup. This does not establish zero operational risk or transfer the result to another lift.
These results belong to one payload, vessel and sea-state case. A project assessment must check clearance, transient loads, available stroke and the relevant crane and rigging limits together.
Case table and published context
| Crane hoist speed | Conventional crane — re-contact | ANTARES quick-lift |
|---|---|---|
| 1–3 m/min | 100% | 0% (0 of 120) |
| 5 m/min | 86% | 0% (0 of 120) |
| 10 m/min | 52% | 0% (0 of 120) |
| 20 m/min | 15% | 0% (0 of 120) |
The quick-lift re-contacted in none of the 120 modelled realisations of that sea state at any speed (95% confidence 0–3% for this model setup). In the modelled snatch the payload leaves the deck at a payload DAF of 1.27 and a peak sling load of 3,118 kN — inside the rigging and crane limits, on 64% of the ANTARES stroke. Modelled in CONSTELLATION as one coupled time-domain load path; deck re-contact evaluated as DNV-RP-N103 §9.5 defines it. One sea state, one case; every lift is sized on its own payload, vessel and sea.
The example was modelled in CONSTELLATION. Equipment capability and the analysed operating envelope are specific to the lift.
Preload, travel, trigger, clearance.
The compensator can already be managing rigging tension before lift-off. The transient then has to satisfy the clearance and load criteria.
Establish preload
Rigging tension is held below the payload’s supported weight while the load remains on deck.
Allow for motion
The planned stroke position leaves travel to manage the heave and carry out the required retraction.
Use the defined trigger
The operator triggers at the favourable relative-motion condition specified in the lift procedure.
Build and maintain clearance
Controlled retraction lifts the load away. The analysis checks the following deck motion, peak loads and stroke use.
The original explanation uses roughly 50% of static weight and ⅓–½ of stroke as illustrative preparation values. Actual preload and travel are specified for the lift; these are not default operating settings.
How the retraction is powered
| Retraction method | How it works |
|---|---|
| Accumulator switch | Low-pressure to pre-charged high-pressure accumulator — sized to retract the payload in question |
| Gas injection | High-pressure gas connected to the working accumulator through a large connection |
| AHC power unit | The HPU generates the additional lifting force |
Retraction force, speed and travel must remain within the assessed envelope. End damping does not replace a check of the transient or available working stroke.
What is the benefit of quick lifting?
Offshore lifts present several challenges. When using relatively slow cranes, recontact between the payload and deck can occur, as unexpected wave or vessel motions may induce rapid movements that result in impacts. Such collisions can damage equipment and lead to costly delays. The quick lifting ability provided by adaptive PHC and AHC units helps mitigate this risk by reducing the likelihood of payload-deck contact.
How does it work?
The payload is attached to a unit configured for quick lift. The illustrative explanation uses tension around 50% of static weight and extension to about 1/3 to 1/2 of the compensator stroke. The actual preload, stroke position and allowable response are established for the lift; the compensator manages rigging tension while the load remains supported by the deck.
The retraction can be done in several ways:
- By switching from a low-pressure accumulator to a high-pressure accumulator that is pre-charged with oil and gas so that it can fully retract the payload in question.
- Connecting high pressure gas (with a large connection) to the current accumulator so that tension is increased.
- Using AHC HPU to generate required additional lifting force.
Quick lifting — frequently asked
What is quick lifting?
Why is quick lifting needed?
When is the quick lift triggered?
How is the rapid retraction powered?
How likely is deck re-contact without a quick-lift?
Which compensators offer quick lifting?
Planning a lift-off that has to happen fast?
Send the crane, payload, supporting-vessel motion and available equipment data. The analysis can assess the trigger condition, clearance history, transient loads and stroke required for the lift-off.
See it in action
ANTARES quick lift — “clear first time” off a heaving feeder barge, simulated in CONSTELLATION
