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Pavan Kumar Sadashiv
Pavan Kumar Sadashiv

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MATSYA-Node: Complete Submerged Hardware Architecture & Marine Components

#hardware #iot #marine #hackathon

MATSYA-Node: Submerged Hardware Subsystems

To adhere strictly to the MATSYA 2026 competition requirements—zero permanent boat alterations, high portability across hull types, and reliability in harsh sea conditions—no holes are drilled into the vessel hull.

Instead, the submerged instrumentation is decoupled into two compact, hydrodynamic sub-assemblies:

  1. Unit 1: The Wet Sensor Pod (Continuous surface and subsurface parameter monitoring).
  2. Unit 2: The Net-Attached Clip (Automated depth profiling and net-drop trigger).
                       +-------------------------------+
                       |   BOAT DECK (ABOVE WATER)     |
                       |  - IP67 Edge Box (Pi / ESP32) |
                       |  - Sony IMX219 Camera         |
                       |  - GPS + IMU + LoRa Radio     |
                       +---------------+---------------+
                                       |
                   +-------------------+-------------------+
                   |                                       |
      (Umbilical 1: Over Gunwale)            (Umbilical 2 / Net Line)
                   |                                       |
                   v                                       v
     +---------------------------+           +---------------------------+
     |   UNIT 1: WET SENSOR POD  |           | UNIT 2: NET-ATTACHED CLIP |
     | - Marine SS DS18B20 Temp  |           | - MS5837-30BA Depth/Press |
     | - Optical Turbidity Probe |           | - Deep Thermocline Sensor |
     | - Piezo Hydrophone        |           | - Net Deployment Trigger  |
     | - Immersion Wake-Up Pins  |           | - Immersion Wake-Up Pins  |
     +---------------------------+           +---------------------------+
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1. Unit 1: The Wet Sensor Pod (Continuous In-Water Sensing)

Physical Form & Mounting

  • Enclosure: Torpedo-profile bullet casing machined from Delrin (POM) or printed in high-density PETG, ballasted at the nose with a 316 stainless-steel nosecone.
  • Mounting Method: Suspended over the gunwale or clamped to the outboard transom bracket using a marine-grade quick-release carabiner. It rides at an operational depth of 0.5 m to 1.0 m below the surface during steaming, trawling, or drifting.

Submerged Components Inside Unit 1

1. Digital Temperature Probe (Maxim DS18B20)

  • Packaging: 316 Marine Stainless Steel hermetic sheath (6 mm x 50 mm).
  • Specs: 9 to 12-bit programmable resolution, +/-0.5 deg C accuracy from -10 deg C to +85 deg C (+/-0.1 deg C calibrated range).
  • Role: Continuous logging of Sea Surface Temperature (SST) to detect oceanographic thermal fronts where commercial fish congregate.

2. Optical Turbidity Sensor (Infrared Photodiode Probe)

  • Packaging: Sealed optical window with hydrophobic/fluoropolymer coating.
  • Specs: 0 to 1000 NTU (Nephelometric Turbidity Units).
  • Role: Quantifies suspended particulate matter and plankton density. Sharp turbidity boundaries correlate strongly with nutrient-rich upwelling zones.

3. Piezoelectric Contact Hydrophone

  • Packaging: Potted in acoustic-grade polyurethane resin.
  • Specs: Frequency response of 20 Hz to 45 kHz.
  • Role: Passive acoustic sensing—captures vessel engine acoustic signatures, eco-sounder pulses, and biological sound layers (e.g., snapping shrimp, pelagic shoals).

4. Dual Saltwater Immersion Pins

  • Packaging: Gold-plated brass electrode terminals spaced 10 mm apart.
  • Specs: High-impedance circuit sensing saltwater conductivity (~4.8 S/m).
  • Role: Generates an immediate digital interrupt to awaken the pod from low-power sleep mode as soon as it enters seawater.

2. Unit 2: The Net-Attached Clip (Tethered / Net-Line Submerged Unit)

Physical Form & Mounting

  • Enclosure: Ultra-compact, pressure-resistant, polyurethane-cast cylindrical capsule (30 mm diameter x 75 mm length).
  • Mounting Method: Clamped with a heavy-duty stainless-steel spring-carabiner directly to the headrope, wing, or cod-end of the fishing net. It descends through the water column during shooting and rests at fishing depth.

Submerged Components Inside Unit 2

1. Piezoresistive Pressure & Depth Sensor (TE Connectivity MS5837-30BA)

  • Packaging: Gel-filled, ceramic-metal hermetic housing rated to 30 bar (300 meters depth).
  • Specs: 24-bit delta-sigma ADC, 0.2 mbar (approx. 2 mm water depth) resolution.
  • Role:
    • Primary Automated Trigger: Net deployment is confirmed automatically when pressure exceeds 1.05 bar (>0.5 m submersion).
    • Depth Profiling: Continuously logs the net's operational depth trajectory (surface, mid-water pelagic, or demersal bottom trawling).

2. Deep Thermocline Sensor

  • Packaging: Direct-contact internal sensor reading through the gel interface.
  • Specs: Fast thermal response (<500 ms).
  • Role: Captures the vertical temperature gradient (thermocline) between surface waters and the seabed, mapping exact thermocline depth for pelagic fish habitats.

3. Marine Cabling, Connectors & Signal Transmission

Component Engineering Specification Practical Justification
Umbilical Cable 4-Core Polyurethane (PUR) jacketed cable with Kevlar central strain member PUR resists diesel oil, fish slime, solar UV, and saltwater hydrolysis far better than standard PVC. Kevlar prevents stretching or tearing under wave drag.
Deck Quick-Disconnect IP68 Push-Pull Marine Circular Connector (Weipu SP13 / M12 4-Pin) Allows deck crews to disconnect and stow the submerged pods in under 5 seconds during net clearing or harbour docking.
Cable Glands PG7 / M12 Nickel-Plated Brass or Nylon Glands with EPDM O-rings Ensures zero water ingress at the cable entry point under dynamic strain.

4. Hardening Against Marine Failure Modes

  1. Zero Mechanical Seams (Solid Resin Potting):
    • Hollow enclosures collapse under water pressure or experience internal condensation due to temperature swings. All internal sensor boards are encapsulated solid in marine epoxy or polyurethane potting compound.
  2. Galvanic & Salt Corrosion Resistance:
    • All exposed hardware is strictly Grade 316 Stainless Steel (A4 marine grade).
    • Dissimilar metals are isolated with nylon washers to prevent galvanic corrosion in seawater.
  3. Bio-Fouling & Lens Protection:
    • Optical turbidity windows are treated with a hydrophobic, oleophobic wipe to shed fish slime.
    • A thin copper ring is mounted around the optical window—copper ions naturally discourage micro-algal and barnacle adhesion without toxic chemical leaching.
  4. Mechanical Snag Protection:
    • Smooth, tapered bullet contours with zero exterior corners or sharp ledges prevent netting, ropes, or sea debris from snagging during net hauling operations.

5. Submerged Parts Specification Summary

Subsystem Component Submerged Location Operating Depth Primary Function
DS18B20 Temp Probe Wet Pod (Transom / Gunwale) 0.5 m to 1.0 m Surface thermal front detection
Optical Turbidity Sensor Wet Pod (Transom / Gunwale) 0.5 m to 1.0 m Water clarity & upwelling assessment
Piezo Hydrophone Wet Pod (Transom / Gunwale) 0.5 m to 1.0 m Ambient bio-acoustics & noise logging
Gold Immersion Pins Wet Pod & Net Clip Surface to 300 m Hardware interrupt wake-up circuit
MS5837-30BA Pressure Sensor Net Clip (Net Headrope/Wing) Up to 300 m Net-drop trigger & vertical depth profiling
PUR Marine Umbilical Water column to deck box Surface to 2 m Power delivery & I2C/1-Wire telemetry

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