Fathom ROV Tether (R2)


This page is the most recent Fathom ROV Tether documentation page. If you have an older version, you may wish to refer to the archived documentation page: Fathom ROV Tether R1 (Retired August 2018).

The Fathom Tether is a high quality tether cable designed specifically for ROVs and other subsea applications. It is neutrally buoyant, has 350+ lb breaking strength, and is embedded with water-blocking fibers to seal any leaks. The tether has a diameter of 7.6mm and is slimmer than the vast majority of comparable ROV tethers.

The tether carries four unshielded twisted pairs (UTP) of 26AWG wire. These pairs are colored and arranged in the same fashion as a Cat5 networking cable including cross-talk resistance. Kevlar strength fibers through the tether allow the tether to carry a significant force without breaking.

The Fathom Tether has a polyurethane outer jacket for better flexibility and adherence to potting material. The tether is sold by-the-meter and also in an ROV-Ready version with a pre-installed cable penetrator, Binder 770 Connector, and tether thimble.

Pololu carries the 3 position 0.1” (2.54mm) Crimp Connector Housings and male crimp pins that may be used for connecting your own devices to the spare tether terminations.

Quick Start

  1. Install the tether on your BlueROV2 or enclosure by lubricating the penetrator O-ring, tightening the nut with a penetrator wrench, and plugging the blue (-) / blue-white (+) twisted pair into the Fathom-X tether interface.

  2. Attached the tether thimble with three thick zip ties and secure the thimble to the ROV frame. It’s very important that the thimble supports the tether so that you don’t pull on the cable penetrator often. Use the [mounting instructions] (http://docs.bluerobotics.com/brov2/assembly/#mounting-the-tether-to-the-frame) for the BlueROV2 as an example.


Specification Table

Item Value  
Tether Diameter 7.6 mm 0.30 in
Weight 0.043 kg/m 0.0287 lbs/ft
Buoyancy in Freshwater Neutral  
Buoyancy in Saltwater Slightly Positive  
Wire Gauge 26 AWG  
Working Strength 35 kgf 80 lbf
Breaking Strength 155 kgf 350 lbf
Minimum Working Bend Diameter 200 mm 8 in
Tether Connection, ROV Side (ROV-Ready Only) 8mm Cable Penetrator  
Tether Connection, Topside (ROV-Ready Only) Binder 770 Plug  
Item Value  
DC Resistance @ 20°C 0.0386 Ω / ft 0.127 Ω / m
Characteristic Impedance @ 1 MHz 120 Ω  
Capacitance @ 1 kHz 16.5 pF / kft 54.1 pF / km
Insulation Resistance @ 500 VDC > 500 MΩ / kft > 1640 MΩ / km
Voltage Rating (Twisted Pair) 300 VDC  
Voltage Rating (Between Pairs) 600 VDC  
Twisted Pairs   Color Binder Connector Pin #
Pair 1 Wire 1 Blue/White 1
  Wire 2 Blue 2
Pair 2 Wire 1 Orange/White 3
  Wire 2 Orange 4
Pair 3 Wire 1 Green/White 5
  Wire 2 Green 6
Pair 4 Wire 1 Brown/White 7
  Wire 2 Brown 8

Section View


Installation tutorial with updated pictures coming soon. For now, please refer to the Fathom ROV Tether R1 (retired) tutorial.