Sea Technology

NOV 2017

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Page 17 of 53

16 st / November 2017 presence (i.e., being nearer to areas of interest) entails substantial challenges. Seabasing seeks to overcome or elimi- nate several of those challenges by es- tablishing a base at sea, independent of shore infrastructure. The seabase is as close as possible to, yet out of range of, possible hostile action. Seabasing introduces a new set of complexi- ties, such as bringing ships, vessels, craft and lighterage together in order to transfer personnel, equipment and cargo from one platform to another, usually in less than ideal weather con- ditions. Standard operating procedures for conducting both military and com- mercial safe operations at sea typically use a statistical approach to establish safe operating limits by setting a sig- nificant wave height (SWH) limit or a sea state limit. SWH is a statistical rep- resentation of the wave heights defined as the average trough to crest height of the top (highest) third of the waves. For example, lightering for ship-to-ship (S2S) transfer of oil cargo will not usu- ally be performed if SWH is above a specified value. Seabasing necessitates a similar SWH limitation for conduct- ing vehicle transfers in an S2S configu- ration where excessive relative roll of the two ships can impart catastrophic twist on the transfer ramp. This statistical approach ensures that potentially damaging ship mo- tions are less likely to occur if the wave heights are statistically below a speci- fied value. Since this approach uses probabilistic and not deterministic rea- soning, to keep it safe, the procedural limit needs to be conservatively set. If, on the other hand, you could deter- ministically forecast ship motions, that is to say, directly measure and forecast specific waves and time the resultant ship motions, then you could set a lim- it based on the actual waves, and not just the statistical representation. Most seabasing operational profiles also dictate a best-heading approach for operations, but in confused seas from multiple directions, this also pres- ents a challenge. To that end, ONR set out with the Environmental and Ship Motion Forecasting (ESMF) program to provide sea-based military and civilian ship and cargo system operators with seaway environmental forecasting in order to predict ship motions and de- termine windows of opportunity for in- ter- and intraship material and person- nel transfer. ESMF is a decision support tool that helps ship crews determine whether it is prudent and safe to con- duct S2S transfer of people, equipment and cargo. The system significantly increases safety while also extending the operating environment for various missions by predicting time periods or ship headings where movement may be conducted despite sea states normally deemed beyond safe operat- ing limits. ESMF provides the ship op- erators with a recommended course/ speed and the ability to make go/no-go decisions for the operational process based on direct knowledge of the in- coming waves and predictions of the resulting ship motions. The result is re- duced risk to the operators, more effi- cient transfer operations and ability for these operations to occur in increased sea state environments. Commercial ESMF Derived from the ONR effort, Fu- tureWaves is the GD-APS commercial variant of the ESMF system. At the core of the FutureWaves system are several key enabling technologies developed UNDERWATER LISTENING SYSTEMS Versatile Acoustic Recorders Real-Time Listening Remote Buoys New Noise Processing Features 25 rue Michel Marion 56850 Caudan - France +33 (0)297 898 580 - International Standard and Guideline Compliant (ANSI, MSFD...) (Photo Credit: U.S. Marine Corps, Alvin Pujols) A U.S. Marine with 1st Marine Logistics Group awaits an M1A1 Abrams tank to be unloaded from an LCAC during exercise Pacific Horizon 2017.

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