An Ocean of Challenges
As part of this incredible undertaking, Friends of the Hunley Chairman Warren Lasch brought together a high caliber team, including the Department of the Navy, the Park Service and Oceaneering International and many other talented organizations. The scope of this committed team includes intensive planning and engineering, design of the recovery system and procedure; procure the recovery system; plus enlist the very finest divers and archeologists.
After lowering two massive 18 foot by 12 foot, custom engineered suction piles to be used as platforms, a truss will be lowered onto the submarine. Nylon slings with inflated foam pillows and sensors (to distribute the weight evenly) will wrap underneath the Hunley, and a crane will lift the entire truss to the surface. Then it will be loaded onto a barge and taken to the Charleston Navy base for the restoration process. It is estimated it will take close to two weeks to fully sling the Hunley.
Oceaneering International, Inc. is an advanced applied technology company that provides engineered services and hardware to customers who operate in marine, space, and other harsh environments.
Following is a synopsis outline of the H.L. Hunley General Recovery Procedures:
1. Personnel and Diving Operations
The Mobilization of a 19-man dive crew and commercial diving equipment. (2 crews will work 12-hour shifts).
A team of archaeologists will be on site full time to lend recovery support and consultation during diving operations.
Divers will start excavation and rigging operations from the bow and work aft.
2. Site Preparation
Excavation of an area approximately 40 feet wide by 130 feet long to expose the top of the Hunley.
Divers set buoys at extreme point of sub for alignment and deployment of the truss during recovery operations.
Excavation will continues until 1/3 of the vessel is exposed.
3. Suction Pile Installation
Suction piles (typically used in deep water oil rig mooring systems) to be installed and work on principle of differential pressures between surface and water depth of the pile.
Top of pile capped with steel structure to support truss while recovery of vessel proceeds.
The advantage of the suction piles is less penetration required than conventional driven piles plus ease of recovery, location accuracy and minimal disruption to the site.
Divers guide piles into place, monitor levelness, etc. Meanwhile topside crew begins suction operation to set piles at required depth.
Foundation integrity for recovery frame stability is ensured with adjustments throughout the process.
4. Recovery Frame (Truss) Mobilization
Truss prepared topside for deployment.
Truss positioned over site by heavy lifting equipment - diver-guided into position straddling the Hunley.
Diver knife truss into sediment with minimum disruption to supporting matrix under Hunley.
Truss in final recovery position when bearing seats land firmly on suction pile.
Divers adjust truss bearing seats/legs for proper alignment and level relative to the vessel.
5. Sling Excavation
Divers expose one to two foot cross section of hull at a time and inspect condition of each section before positioning support rigging.
Once custom support is considered, a 12" wide fabric sling is draped under exposed section of hull. One end of sling has section of chain allowing for length adjustment and to allow rigging to make contact with the hull. (Chain will not make contact).
Each sling assembly includes a load cell to monitor the amount of tension applied to the rigging.
6. Load Cells
Each load cell (attached to each sling) will be monitored by computer at topside.
Load cell monitoring provides data regarding individual sling tension, total weight of the truss load and alarm signaling during recovery.
Two-way communications from diver to topside personnel enables divers to adjust tension in each sling - which is critical to ensure load of Hunley is distributed evenly to the truss.
This system also utilized during preservation phases of the project. Individual slings can be loosened for preservation considerations then re-tensioned to the initial value - minimizing hull distortion.
7. Foam Installation
A foam system designed by Flexible Products, Inc., will be utilized for stabilization and protection of vessel components.
Foam is injected into containment bags which are attached to the slings.
Foam bags support and conform to vessel at critical points including dive planes, stern and keel.
Upon optimum installation of required slings/supports plus with analyzed load cell data to determine peak stabilization, and weather/sea conditions - divers rig a 6-sling bridle to truss.
Divers move to safe area, and recovery frame lift takes place.
Hunley is positioned upon transport barge.
Support personnel stabilize the Hunley in truss using tension straps at critical locations to prevent movement during transit
Sprinkler system is put in place to continually soak the vessel with seawater to minimize oxidation during transit to Port of Charleston.
9. Recovery Epilogue
This is a one-of-a-kind recovery. Thousands of questions are answered before these processes take place. Developed under worse-case scenarios, these unique recovery plans are always under careful scrutiny and studied physically, and via computer models. Dangers to both the vessel and the crew are possible at any given moment - so every precaution has been taken to ensure the safety of this historical project -- one of the only of its kind on the planet today!
Finding The Hunley
Obstacles to Recovery
A Plan Evolves