As a heave compensation specialist, at TENSA, we receive a lot of client’s enquiries on the right product to choose for different lifting applications in offshore operations.
The following table outlines the key criteria you can use to decide on the right heave compensation product for your project:
Choosing the right system
Dynamic load reducer (DLR) is used with offshore cranes to reduce the dynamic loads associated with lifts from moving vessels.
Passive heave compensation (PHC) is generally used to support a stationary load or to reduce motion when the lifting system is moving, for example, when lowering subsea equipment to the seabed. It is also used to minimise loads in the splash zone.
Active heave compensation (AHC) is designed to hold a load stationary relative to earth and is particularly useful for lowering a boat supported load to the seabed or connecting load to a fixed structure.
Misconception #1: To reduce crane dynamic loads, a long stroke is needed
The optimum cylinder stroke is between 1m and 1.5m as the shock absorption is most effectively handled over a stroke of 0.5m. The extra stroke allows the system to handle a wide load range without adjusting the setup as the cylinder force increases as the rod is extended.
Misconception #2: Active heave compensation is a good technique to reduce dynamic loads in the splash zone
In the splash zone, you must use passive heave compensation as AHC will hold a load stationary to the seabed, whereas the load needs to stay stationary relative to the water surface to minimise loading.
Misconception #3: Active heave compensation is suitable for supporting loads connected to the seabed from a moving vessel
AHC is never perfectly accurate and can fail. Hence any rigid connection between a vessel and the seabed could be overstressed. A passive heave compensation device should be included in the connecting string.