# Tether Selection Notes

**Author:** Eric Martin  
**Project:** Benthic Observation System  
**Last Edit:** 31 January 2017  
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## Requirements

+  Tether must allow for successful working depths of 300-m.
+  Tether must accommodate power transmission of 600-W.
+  Tether must have signal conductors for ground fault interruption feedback.
+  Transmission through the tether must allow for control communications and SD video streaming.
+  Tether and management system must integrate with regional-class ships of opportunity.
+  Tether must double as lifting strength member. 
+  Tether termination must allow for desired bottom behavior. 

## Derived Requirements

### Mechanical 
1.  Length of the cable must allow for field re-termination, and catenary required for the typical watch circle of a region-class vessel. 
	+  Watch Circle: ~20-m
	+  Flying Lead at bottom: ~10-m
	+  Re-termination minimum length: ~2-m
	+  Resultant Minimum Tether Length is 350-m, design maximum will be 400-m.
+  Recovery means that the cable must have a working tension rating of the final design weight of the lander, estimated at 100Kg in air. Minimum safe working load is near 2kN. 
+  Winch much accommodate 400m of cable, slip ring, and be able to support the combined in water weight of the cable and lander.
+  Haul Speed must be at least 30m/min. 
+  Current Design Weight Estimates:

	| Item      | Air Weight  |  Water Weight | 
	|:--        |:--          |:--            | 
	| Lander    | 100kg       |  ??           |
	| Cable     | ??          |  ??           | 

+  Mobilization Requirements? 
+  For specified weights double for dynamic load rating.
+  Wire must be 5x rated for dynamic load rating.


### Electrical 

1. Chad has expressed a desire for minimum 16AWG/4C or 14AWG/2C as conductors for the 400VDC 600-W Supply.

	| Wire | FEP Single Conductor Ampacity[^From NEC Table 310-16] | Total Current Rating | DC Resistance Ohms/1000-ft[^From http://www.standard-wire.com/downloads/swc_catalog.pdf] | 2-Way Transmission Loss 400-m @ 600-W |
	|:--       |:--  |:--  |:--   |:--    |
	| 16AWG/4C | 18A | 36A | 2.28 | ~9 V  |
	| 14AWG/2C | 25A | 25A | 2.88 | ~12 V |

2. Single Fiber or other medium capable of multiplexing 8 SD video streams or 1 Gigabit data rates. Multiple fibers preferred. 
3. 2 Small Conductors (~24-22AWG) are required to create the GFI circuit.

### Data

1. I looked into leveraging an adsl solution to investigate using coax vs the electro-optical cable. V/ADSL speeds max at 25-Mbps, which would limit performance greatly. SD streams are typically 6 Mbps each. Not to mention the current limitations of OTS components for this type of solution. 400VDC 600W would be very difficult, and require complex custom board design. 
2.  Need Data Capacity for 4 simultaneous video feeds (4x6Mbps)