Can be attached to existing tether(s) to increase length
The Homeplug communication protocol has been tested successfully to 300m but distances over 100m may cause intermittent communication dropouts or other failures not yet discovered.
Having a 100m tether is hardware insurance that your OpenROV does not go too deep. Depths at or near 100m may cause critical failure of the main electronics tube or battery tubes. If using extended tethers, keep an eye on depth using the IMU/Depth Sensor or other means.
This tether sinks, so be careful not to get caught on rocks, debris and especially not coral when using extra tether. To mitigate this problem consider using Neutrally Buoyant Tether.