SITIS Archives - Topic Details
Program:  SBIR
Topic Num:  N102-155 (Navy)
Title:  Towed Array Fishing Net Entanglement Prevention or Damage Reduction
Research & Technical Areas:  Sensors

Acquisition Program:  SURVEILLANCE TOWED ARRAY SENSOR SYSTEM (Low Frequency Active) ACAT II
  Objective:  Research and develop a method and/or apparatus to prevent or mitigate towed array system damage from fishing net and hook entanglement
  Description:  Fishing nets plague US Navy operating areas in the Pacific Fleet (PACFLT). They entangle Navy towed arrays, especially the twin-lined (TL -29A) array used by SURTASS. Entanglements occur with little or no warning. The entangled array coupled with the constant tow of the vessel causes enormous stress on the towed array and cable. The stress either snaps the array and/or significantly damages individual modules. The costs of net entanglements are monetarily significant, impact mission critical operations, and reduce PACFLT ASW readiness. Disentanglement operations temporarily halt operations with similar consequences. The Navy is committed to lessening the likelihood of net entanglements. This topic solicits innovative solutions beyond the current state of the art that improve array survivability. Current solutions consist of the following. (a) SURTASS Headline and Roll Control System (SHARC), a rigid system between the two arrays that allows the system to potentially “fly” over the nets rather than collapse in them (as paravanes did). However, the SHARC system can act as a net collector. The system has been useful in preventing collapse of the arrays (and further more expensive damage) but still collects nets and often can “push” fishing nets further down the array. ( b) Preventative tools that measure spikes in tension. The tensiometer that is currently in use measures tension in the array, which is triggered by an entanglement that has already occurred. This device helps to prevent further damage caused by entanglement by alerting the crew to stop the ship and retrieve the array to remove nets. (c)Modifications to smooth array hard points, referred to as the y-joint modification, consist of a hard plastic shell (over the tow cable y-joint). It provides a smooth surface (over a once blunt design) and lets the nets glide over this area. However, there are still areas of the array that are prone to net entanglements (that now occur further down the array). (d)Hardware and sensors are used to locate and recover lost arrays, but that goal is not within the scope of this topic. All of these items provide help in dealing with net entanglements and can minimize impact but none provide a solution to prevent entanglement from occurring. There is still no known solution to prevent entanglements. Using the technology listed above, the Navy has attempted to “steer” the net entanglements and damage to less costly, less critical parts of the array. However, net entanglements still occur and the damage often leads to both potential array loss and/or the array having to be removed from the ship to be repaired. Offerors are asked to research, develop and demonstrate new solutions to the stated problem. Solutions may include location detection (of nets), preventative devices, safe cutting devices, avoidance devices and/or damage mitigation schemes.

  PHASE I: Conduct a feasibility study of how the proposed solution would prevent net entanglements and reduce damage or loss. The feasibility of the proposed solution should be visually supported by a basic working model, CAD drawings at the conceptual level, or simulation. Assess and analyze the remaining research and development required to implement the proposed solution. Clearly identify how the analysis and study address the current Navy’s towed array system and system requirements.
  PHASE II: Implement the Phase I design in an Engineering Development Model (EDM) and test the EDM in a realistic environment, which might include lake or basin testing. Incorporate lessons learned from these tests into a full system design. Complete some small tests or models to demonstrate that the lessons learned were incorporated into the system.

  PHASE III: Fabricate a production representative towed array system for lake and/or at-sea testing onboard a SURTASS vessel. Successful completion of this waterborne testing will enable the integration of the net mitigation solution into the Navy’s towed array systems. PRIVATE SECTOR COMMERCIAL POTENTIAL/

  DUAL-USE APPLICATIONS: Net mitigation applications can have use in any towed array application including the seismic oil exploration industry. In addition any research attained throughout this process may be beneficial to any commercial or environmental agencies/sectors concerned with fishing net entanglement.

  References:  Patents cited represent different approaches and are not to be taken as endorsements of the patent or the patented approach. 1. “Adaptive Methods Develops SHARC Tow System” 2. “Gel-Filled Seismic Streamer Cable” 3. “Lateral Force Device for Underwater Array” 4. “Thin-Line Towed Array Force Measurement Apparatus and Method”

Keywords:  entanglement avoidance; towed arrays; SURTASS; fishing nets; array damage mitigation; array damage avoidance

Additional Information, Corrections, References, etc:
Ref #5: TL-29A towed array drawing. (Uploaded in SITIS 6/2/10.)REF N102_155 TL_29A Array SHARC.ppt
Ref #6: Photos of fishing net entanglements, 5 photos. (Uploaded in SITIS 6/2/10.)REF N102_155 Photos 5.pdf

Questions and Answers:
Q: If the proposed solution involves the need to locate fishnet, are there any detection schemes that are forbidden due to conflict with the tow array?
A: Anything that has acoustic impact on towed array performance (i.e. anything generating loud or repetitive noises).
Q: 1. Can we get a general arrangement drawing of the towed array, twin line rigging and towcable?

2. Are certain types of net/line more of a problem than others? If so what are the general characteristics (e.g. size of mesh, material, etc.)

3. What is the typical tow speed?

4. Is towing off of two separate leaders/winches an option?

5. Are there photos available of past fishing net entanglements?
A: 1. Towed array drawing has been uploaded in SITIS as new REF 5.

2. We run into all kinds of nets. Long line hooks damage array hose but all types of nets cause entanglement. Nets consist of all types of material and sizes. There is no consistency.

3. Typical tow speed while passive array is deployed is 3 - 7 knots.

4. We already tow from two leader cables. Adding an additional winch depends on size and impact to ship structure.

5. Five photos have been uploaded in SITIS as new REF 6.
Q: 1. Would it be possible to add dimensions (even approximate dimensions) to the drawing provided?

2. How far behind the ship is the array towed?

3. Is the SHARC always used? Did it take the place of the paravanes?

4. Does our SBIR proposal have to be a single solution or could we propose two ideas which would be refined and compared as part of the Phase 1 study?
A: 1. We do not currently have a drawing with dimensions but can update the existing drawing with dimensions. This will be provided SEPCOR.

2. This depends on the area of operation. The tow cable scope can range anywhere from 500ft - 4500ft.

3. The SHARC is almost solely used for 1.5M and 2.2M headline spacing. Paravanes are still used for larger spacing. 4.4M SHARC is being developed. In the future, paravanes will only be used as a back-up or for 8.0M spacing.

4. Two ideas would be accepted (that could be later refined).
Q: 1. Was net/line entanglement an issue when you were towing a single line array i.e. are the current entanglement problems the result of the switch to the twin line configuration?

2. What is the approximate tow depth of the array?
A: 1. Net entanglement can still be an issue with single line (more often hooks embedded in the array). However, switching to twinline has caused this to be a much greater issue.

2. This depends on the area of operation. The depth can range anywhere from 40ft - 2500ft.
Q: In an attempt to avoid entanglement, has the Navy done field testing of towing two independent HLAs (completely separate, no bridle). If so what were the results?

If not was the idea considered?
A: The short answer to the question is no, the USN has not tried tandem tow for SURTASS. It has been used for other programs.

Tow with independent HLA has been considered. This is a common practice for tandem tow by the oil and gas industry vessels. It would be nice but would require to many changes to the SURTASS system.
This approach has typically been done using multiple winches and to sheaves.
In the present system configuration this is not considered practical. We are limited by the space and weight required.

Similarly, this approach often requires that you have a "active" mechanism to maintain the proper array depth and separation. This requires major modification to our present array designs. Again, no practical approach to solve this problem has been identified.

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