The common methodology adopted to test the Underway Replenishment (UNREP) equipment aboard ship is to utilize a dockside or floating crane, a set of test weights and a preventer line to control the angle of the test loads applied, and to ensure that the suspended weights from the crane are kept truly vertical so as not to overload the crane.
The preventer line has to be attached to a strong point on the wharf or floating crane barge, and has the potential to cause a mishandled crane to be overloaded and damage the jib or slewing ring. The test equipment and rigging also has to take into account the height difference between the deck level, test points, availability of strong points for fixing the preventer lines and availability of a suitable crane able to support the full test weight. This methodology is traditionally time consuming and expensive.
All of these problems can be overcome by the use of a gin pole acting as a strut to convert the water Weights into the required pull on the UNREP pad-eye or sliding block. Altering the length of the gin pole would facilitate testing angles in the vertical plane and fixed rigging points on the vessel with adjustable rigging wires would permit the tests to be conducted at a variety of angles fore and aft of a beam, all with the minimum of difficulty.
In addition, the use of a gin-pole would preclude the necessity for a crane to support the test weight other than for rigging the test. This removes the likelihood of shock loading the crane from the impulse of a dropped load should the item of equipment being tested fail. The use of water bags will allow the gradual application of load, together with monitoring key components of the system during the test, thus ensuring that UNREP testing does not create a hazardous situation.
System Description
• Adjustable length gin pole and Water Weights bag
• Load attachment plate
• Base plate and deck load spreader
• Lateral restraint rigging
The gin pole is erected with its rigging to fixed points on the ship such that the gin pole acts to strut the test load off the vessel and convert the vertical test load to a horizontal pull. The UNREP testing can then be carried out very simply by adjusting the length of the gin pole with the addition of intermediate sections to achieve the ±30ยบ vertical alignment about mid-position and by adjusting the lateral restraint rigging to alter the fore and aft alignment of the test.
The use of a gin pole allows the resolution and transfer of the test loads into the internal structure of the vessel by the base plate and deck load spreader without the need for a preventer line to a dock side fitting or bollard. Load monitoring and measurement can be integrated with the gin pole and rigging to ensure the specified test loads are being applied to the UNREP system to meet the design intent.
Water Weights also has the ability to provide a full monitoring suite of instrumentation during testing to determine the ongoing structural integrity of the UNREP system. Typical techniques include the use of Acoustic Emission fingerprinting and monitoring during load applications, instrumented load pins in the primary load paths, rotary encoders for accurate measurement of line angles and telemetry load links able to remotely report the loading regime under which the test is being carried out.
Note: The company is in the process of fitting a full set of monitoring equipment to a Royal Navy Type 23 frigate to monitor the actual loads in real time experienced by the Replenishment At Sea (RAS) system during a period of sustained use under a variety of sea states, load transfers, connected platforms and operational environments. This is part of a data gathering exercise to support the development of a higher load capacity and throughput RAS system for the Royal Navy future carrier project.
For more info visit: http://www.waterweightsinc.com/files/files/US_Downloads/UNREP_Testing.pdf
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