Landing Speed Reduction

When a load reaches the seabed, it transitions from a dynamic hanging system to a static supported structure. The landing impact generates forces that depend on the velocity at touchdown, the stiffness of the structure and seabed, and the mass of the load.

Even moderate landing speeds can cause problems:

• Equipment damage — Subsea manifolds, trees, and templates contain precision-machined surfaces and seals that are sensitive to impact loads.
• Structural damage — Mudmats and foundations can buckle or over-penetrate the seabed if impact forces are excessive.
• Alignment failure — If the load bounces or shifts on landing, it may not settle in the correct position for subsequent tie-in operations.

Without heave compensation, the landing velocity is determined by the vessel’s heave motion — which the operator cannot control. This often means waiting for very calm weather, or accepting the risk of a hard landing.

A heave compensator reduces landing speed through two mechanisms:

• Heave isolation — By decoupling the load from vessel heave, the compensator eliminates the dominant source of uncontrolled vertical velocity. The load descends at the winch lowering rate, not at the combined rate of winch and heave.
• Increased damping — During the landing phase, the compensator’s damping can be increased to slow the load’s descent, providing a controlled final approach speed.

The result is a predictable, controlled landing at a velocity determined by the operator, typically 0.1–0.5 m/s, regardless of the sea state. This dramatically reduces impact forces and improves the reliability of the landing operation.

A typical subsea landing sequence using a heave compensator proceeds as follows:

• Approach — The load is lowered to a few metres above the seabed with the compensator providing normal heave compensation.
• Final descent — The compensator damping is increased and the winch pays out at a controlled rate, reducing the effective landing speed.
• Touchdown — The load contacts the seabed at low speed. The compensator absorbs any residual heave motion, preventing the load from bouncing.
• Set-down — The crane wire tension is gradually reduced, transferring the full load weight to the seabed. The compensator prevents snap loads during this transition.

For more on the broader challenges of getting a load to the seabed safely, see our guides on subsea lifts and splash zone crossing.

The landing phase favours compensators with adjustable damping — the ability to increase resistance during the final approach and then reduce it for normal heave compensation during other phases.

Norwegian Dynamics ANTARES is particularly well-suited to landing operations. Its adaptive gas spring maintains optimal heave compensation during lowering, whilst its adjustable damping system provides controlled deceleration for landing. The piston rod locking function also allows the load to be held securely after set-down if the crane wire needs to remain connected.

For operations where maximum control is required — such as precision connector mating or landing on an existing structure — Norwegian Dynamics active heave compensator provides the highest level of motion control, allowing the operator to set an exact lowering velocity. For help choosing between these options, see our compensator selection guide.