Fat Line Towed Array Aft Stabilizer
Navy SBIR 2019.1 - Topic N191-035
NAVSEA - Mr. Dean Putnam - dean.r.putnam@navy.mil
Opens: January 8, 2019 - Closes: February 6, 2019 (8:00 PM ET)


TITLE: Fat Line Towed Array Aft Stabilizer


TECHNOLOGY AREA(S): Battlespace, Electronics, Sensors

ACQUISITION PROGRAM: PMS 401, Submarine Acoustic Systems Program Office

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop a passive or active control system that stabilizes the aft end of towed fat line arrays during operational tow conditions.

DESCRIPTION: Fat Line Towed arrays often operate in hydrodynamic conditions where the flow field is turbulent. Non-uniform flow causes the aft end of the towed array to experience low-frequency motion (i.e., roll, and lateral and vertical motion). These high levels of movement negatively affect the performance and reliability of towed arrays and associated processing by impacting the acoustic performance of the array, degrading performance of the magnetic heading sensor in the aft end of the array, and causing additional stress and failures for components and modules in that area. A stable array is required for accurate understanding of the location of detected signals and improved reliability of the aft heading sensor for array shape estimation. In addition to improving system acoustic performance, an aft stabilization device (stabilizer) should reduce mechanical stress and associated failures in the aft components and modules in the array. The reduction in failures for the towed array components will reduce system lifecycle costs by decreasing the number of repairs required due to failures; increasing the time between failures; and reducing the costs associated with the removal and installation of the system. The Navy is looking for an innovative solution that provides a passive or active control system (stabilizer) for the aft end of towed fat line arrays that stabilizes the low-frequency motion during operational tow conditions. This solution should also be compatible with current fat line array handling and stowage infrastructure.

Commercial towed systems do not operate in the same speed regime or flow field as military towed arrays and do not have the same constraints on size or compatibility with existing array handling infrastructure. The designs and concepts used in the commercial sector are not applicable to this application.

Critical aspects of the technology development for the stabilizer system include control methods and devices; flow analysis of array state in a non-uniform (turbulent) flow field; and feedback and control to mitigate deleterious motion caused by the turbulent flow field. The towed arrays for which aft stabilization is desired are approximately 300 feet long with a diameter of approximately 3.5 inches. The representative specific gravity for developing concepts is 1.025 +0.07/-0.00. The outer surface of fielded fat line towed arrays is smooth.

Critical performance factors of the technology development for the stabilizer system include tow stability, compatibility with the fat line stowage tube and handling, and retention of full system performance, reliability, and compatibility with the towed array. The stabilizer needs to be designed such that any failure modes such as loss of lift or drag will not negatively impact the towed array performance.

The stabilizer system must fit within stowage tube and bell mouth physical limitations. The bell mouth is a funnel shape with a bend radius of ~ 60 inches. The stabilizer is deployed from and pulled into a stowage tube with an inside diameter of approximately 6.0 inches at a rate up to 100 feet per minute. The material for both the bell mouth and stowage tube is a Copper-Nickel alloy. A bell mouth at the interface between the tube and ocean environment mitigates kinking of the array and its tow cable. Deployment of the array itself occurs by allowing the ambient differential pressures to pull the array from the tube, and the stabilizer must not interfere with this passive deployment evolution. To avoid negative impact on reliability, the stabilizer system must survive a minimum of 100 deployment and retrieval evolutions without damage. The size of the stabilizer system is limited to a maximum diameter of 3.5 inches and a length of 4 feet when inactive or retracted. No more than 100 volts and 0.25 amps of system power are available for stabilizer control and activation. The stabilizer system must be able to operate for 30 days continuously under typical tow conditions. Typical tow conditions are speeds from 5-20 knots with most of the time spent at mid-range speeds. The flow input for the stabilizer will be based on the Turbulent Boundary Layer (TBL) developed by the array (cylindrical tow) forward of the stabilizer.

To be deemed suitable for use, the stabilizer system cannot generate acoustic noise or mechanical vibration that negatively impacts the overall system (or magnetic heading or acoustic sensors) performance. Proposers should identify the anticipated acoustic noise and vibration levels associated with their proposed solution. Failure of the stabilizer system should not preclude the retrieval or deployment of the towed array from the stowage tube. The stabilizer is required to mate with the towed array modules. The stability and performance of the device are higher priority than the specific array interface.

The purpose of the stabilizer system is to mitigate low-frequency movement and oscillations (roll) of the towed array and demonstrate this ability during testing under actual tow conditions with an instrumented array provided by the Government. The environmental compatibility of the unit testing will be in accordance with MIL-STD-810G [Ref 4]. The Government will evaluate the compatibility of the stabilizer system with current deployment and retrieval equipment and procedures by using a mock-up of the stowage tube during static and towed conditions.

The Phase II effort will likely require secure access, and NAVSEA will process the DD254 to support the contractor for personnel and facility certification for secure access. The Phase I effort will not require access to classified information. If need be, data of the same level of complexity as secured data will be provided to support Phase I work.

Work produced in Phase II may become classified. Note: The prospective contractor(s) must be U.S. Owned and Operated with no Foreign Influence as defined by DoD 5220.22-M, National Industrial Security Program Operating Manual, unless acceptable mitigating procedures can and have been be implemented and approved by the Defense Security Service (DSS). The selected contractor and/or subcontractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances, in order to perform on advanced phases of this contract as set forth by DSS and NAVSEA in order to gain access to classified information pertaining to the national defense of the United States and its allies; this will be an inherent requirement. The selected company will be required to safeguard classified material IAW DoD 5220.22-M during the advance phases of this contract.

PHASE I: Develop a concept for a stabilizer system that must address the critical performance factors for a fat line towed array as described in the Description, including the design of any control system required. Demonstrate feasibility by analysis and modeling of key elements. Develop a Phase II plan. The Phase I Option, if exercised, will include the initial design specifications and capabilities description to build a prototype in Phase II.

PHASE II: Design, develop, and deliver a prototype stabilizer system. Ensure that the prototype demonstrates its ability to reduce the array aft end motion based on the requirements in the Description. Perform the demonstration at a Government- or company-provided facility.

Conduct the final system validation on a Navy ship that uses towed arrays. Monitor the performance of the array using the existing array sensors and compared to baseline measurements. Measure the reduction in array aft end motion and vibration during system performance testing to quantify the overall stabilizer performance. Assess the reduction in damage to sensors and modules in the array during the testing of the stabilizer performance. Prepare a Phase III development plan to transition the technology for Navy production and potential commercial use.

It is probable that the work under this effort will be classified under Phase II (see Description section for details).

PHASE III DUAL USE APPLICATIONS: Assist the Navy in transitioning the fully functional stabilizer system for Navy use. Support installation of the stabilizer system into a Government-defined fat-line towed array and provide assistance during laboratory and shipboard test events.

The developed technology is applicable to any towed system where aft end stability is required. One example would be the stabilization of dual array systems where the relative position of the two arrays impacts system performance. The stabilizer design could be re-sized and modified to work with this application. Towed arrays are used in undersea surveys, such as oil exploration.


1. Lemon, S. G. "Towed-Array History, 1917-2003." IEEE Journal of Oceanic Engineering, Vol. 29, No. 2, April 2004, pp. 365-373. http://ieeexplore.ieee.org/abstract/document/1315726/

2. Obligado, Marin and Bourgoin, Mickael. “An experimental investigation of the equilibrium and stability of long towed cable system.” New Journal of Physics, Volume 15, April 2013. iopscience.iop.org/article/10.1088/1367-2630/15/4/043019/pdf, 15 April 2015; http://iopscience.iop.org/article/10.1088/1367-2630/15/4/043019/meta

3. Bearman, P.W., Huera-Huarte, F.J., and Chaplin, John R. “The Hydrodynamic Forces Acting on a Long Flexible Circular Cylinder Responding to VIV.”

4. MIL-STD-810G, Department of Defense Test Method Standard: Environmental Engineering Considerations and Laboratory Tests, 31 Oct 2008. https://snebulos.mit.edu/projects/reference/MIL-STD/MIL-STD-810G.pdf

KEYWORDS: Hydrodynamic; Towed Array; Flow Stabilizer; Towed Dynamics Control System; Flow Analysis; Turbulent Boundary Layer; Fat Line



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