Hydrophone Array Repair(ed!)

In 2013, the Bangarang’s towed 2-channel hydrophone array was incapacitated after a tragic run-in with a particularly forceful hydraulic flow over Verney Passage’s northern sill during July’s spring tide. Lesson learned, we are returning this summer with a repaired and improved towed array as well as about 3 or 4 back up acoustic recordings systems. Advisor Jay Barlow and I have been working on the repairs for the last few weeks, and today the job is done.

OBJECTIVES of REBUILD:
1. Resplice a broken section of the array’s 100m cable.
2. Strengthen the weak points at all connections in the array.
3. Add a depth sensor to the oil-filled array.
4. Replace all connectors with 9-pin connectors, to accommodate depth sensor wiring.
5. Build and splice in a pre-amplifier in the oil-filled array, boosting the received signals far above self-noise in the electronics. The preamplifier would add 20dB gain nd a 480 Hz soft high-pass to both channels.
6. Replace end piece with brass plug and run a seawater ground from the cable to it through the array.

STEP 1: BUILD SILICONE MOULD of the 3M splicing kit, to have a repair mould on board this summer.

Photo Jan 27, 9 30 06

A 48-hr process. Followed the procedure used here.

Photo Jan 27, 11 24 41
(Not pictured — build a plaster cast around mould for strength)

STEP 2: PREPARE SPLICE

Photo Jan 30, 10 20 17

(Always slip heat shrink on the cables BEFORE you splice!)

Photo Jan 30, 10 19 38

STEP 3: POUR 3M PLASIC CAST AROUND SPLICE

Photo Jan 30, 16 42 37

Photo Jan 30, 16 45 52
(Clean up cast with a box cutter for sleak hydrodynamics underway)

STEP 6: REPLACE CONNECTORS

Photo Jan 17, 10 27 12

STEP 7: BUILD & TEST PREAMP, BUY DEPTH SENSOR (Not pictured)

STEP 8: DRAIN CASTOR OIL FROM TUBE
Have spill response and mitigation gear handy!

Photo Feb 12, 9 10 41

STEP 9: INSTALL PRE-AMP & DEPTH SENSOR
Pull array out of tubing, and get very messy as you do. Triple check before you solder, and have many rolls of paper towel within arm’s reach.

Photo Feb 12, 9 28 53

STEP 10: POUR OIL BACK IN

Photo Feb 12, 11 53 02

Make sure to get all the air bubbles out! This takes a few hours.

Photo Feb 12, 11 58 43

STEP 11: GROUND, INSTALL & SEAL BRASS END PIECE
Using the Barlow Machine Shop lathe, cut the plug to the proper diameter and add barbs.

Photo Feb 17, 14 09 28

Before you seal it up, do some tests. Time to break out your best humpback feeding call:

Screenshot 2014-02-17 15.09.13

Beautiful! Fingers crossed that it sounds as good as it looks, use heat-shrink band clamps to re-seal both ends of the oil array and add heat shrink at the connections. Start getting excited.

Photo Feb 17, 14 55 46

STEPS 11 – 13: SIGH IN RELIEF, PACK IT UP, and CHECK IT OFF THE LIST.

Photo Feb 17, 15 17 33

Jay’s generosity with his time, knowledge, lab resources and hospitality made this repair possible.

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