Design and Testing of a Snap Load Alleviator for a Submarine Rescue Vehicle Handling System

The snap load alleviator (SLA) is a passive, hydraulic, shock-absorbing backup system to mitigate snap loads in a launch and recovery system for a manned submersible. The SLA is part of a mitigation strategy for potential failures identified as part of a hazard analysis. This analysis considered failures in the active heave compensation system, which is the primary approach to compensate for vessel heave in rough seas. To reduce the size and weight of the SLA, it has been designed with a much shorter stroke than the magnitude of expected vessel heave. The SLA has low inertia and mitigates only the leading edge of a snap load while the rendering function of the lift winch, which has much higher inertia, deploys additional lift line before the SLA runs out of stroke. Tight coupling of the dynamic properties of the SLA and the lift winch is required for this approach to succeed. The rationale and the design of the SLA is presented. Computer simulations demonstrate the snap loading problem and validate the proposed solution. Hardware testing to qualify the design and to corroborate the simulations is described.