Quick Lifting

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 the adaptive PHC or AHC. Tension is kept at say 50% of static weight causing the rod to extend when the crane is lifting. Extension is then done until about 1/3 to 1/2 of compensator stroke is reached. The compensator is now passively keeping tension in the rigging around 50% as the vessel is heaving up and down. At a top of a wave (recommended) the quick lift is activated by the user by the click of a button. The piston rod is the retracted to the fully retracted position in a controlled manner.

The retraction can be done in several ways:

  1. By switching from a low pressure accumulator to a high pressure accumulator that it pre-charged with oil and gas so that it can fully retract the payload in question.
  2. Connecting high pressure gas (with a large connection) to the current accumulator so that tension is increased.
  3. Using AHC HPU to generate required additional lifting force.
It is important that the tension is not too high, which could cause unnecessary dynamics. Norwegian Dynamics compensators are equipped with end damping that will prevent damage to the compensators, but it is in any case good practice to avoid this.