How does SeaChannel work?
The current system runs from 12V, although solar powered and Lithium battery solutions will also be offered. A electronic invertor digitally generates the sinewave power carrier at 500Hz. Data carrier signals run at higher frequencies and digital signal processing techniques are used to retrieve and demodulate the data on a continuous basis, and in the presence of the power carrier signal. In this way, both power and simultaneous bi-directional communications are maintained to the underwater unit. Both the shore (or boat) equipment and underwater terminal have two connections. One is a short connection to a sea electrode at each end of the link, and the other is an electrical connection to the wire rope itself. In this way a complete circuit is formed, with the sea itself acting as the return circuit.
Making and connecting a SeaChannel Tether
The system is designed to run with off-the-shelf shrouded stainless steel wire rope. A stainless steel terminal can be provided, which is designed to be mounted on a flat non-conducting surface of the underwater unit, such as a plastic housing. An o-ring provides the waterproof seal. This terminal has a reverse M5 thread to allow connection to a turnbuckle (rigging screw) which is, in turn, connects to an M5 stainless steel stud, which itself is crimped to the wire rope. The terminal assembly does carry a low AC voltage when in use and must be insulated from the sea. There are a variety of methods to do this, including heatshrink, insulation tape, or self amalgamating tape, depending on the application. For deep (high pressure) applications, a gel filled insulating assembly is envisaged, and these are under development. As such, and with a hand crimp tool, a SeaChannel connection system can be cut to length and fit to the underwater unit in the field. The use of a turnbuckle means that the underwater equipment doesn’t have to be rotated when it is connected to the wire rope.
The system is also designed to be tolerant of sea electrode corrosion. Our tests, have indicated that sea-electrodes should last at least a year under normal operation. These are being designed to be replaced in situ by a diver. Slow erosion of the sea electrode is a natural process simply as a result of the boundary of electrical metallic conduction and ionic conduction through the sea.
Successful freshwater trials have been done, but whereas the sea is relatively constant salinity, freshwater varies considerably in its (much lower) conductivity. In freshwater, larger electrodes are required, and the ability the transmit power is reduced.