Coil-Cord Conductors on Compliant Elastic Moorings

High stretching rubber tethers are one means of supplying the required compliance in coastal buoy moorings. However, a major disadvantage of the elastic tether approach has been that electrical signals and power could not be carried along the elastic tether to allow data from all depths to be sent to the surface buoy for telemetry to shore. To overcome this difficulty, a coil-cord design concept was tested as part of an ongoing observatory/monitoring effort 13 km off the coast of New Hampshire in 55 m of water in the open Gulf of Maine. In this application, the rubber tether with an added coil-cord was located near the top of the mooring to allow the buoy to move more freely with the sea state to obtain better wave statistics. An environmental sensor package located below the rubber tether was hard-wired through the coil-cord to the surface platform, allowing its data output to be regularly telemetered to shore together with the buoy's meteorological, sea surface temperature and salinity and accelerometer data. Near real-time access to the mid-water data is much more useful for the nearby aquaculture than access to archived data collected by internally-recording in-water sensors which are available only every three to four months when the mooring is serviced. The coil-cord/compliance assembly was constructed with four parallel elastic tethers, each 14 m long, with the coil-cord spiraled around one of them. The coil-cord was terminated at each end with standard underwater connectors, and attached to a bridle and the tether splice to prevent movement relative to the tether at each end. Also, the coil-cord was securely attached to the tether with self-vulcanizing tape at two places along the tether. This is done to prevent the coil-cord from working its way down the tether, causing uneven stretch and loading response and possibly local abrasion of the rubber tether around which the coil-cord is wrapped. The top connector on the coil-cord was attached to the surface buoy and the bottom connector to a Sea-Bird SBE-16Plus Seacat measuring temperature, conductivity, dissolved oxygen, optical backscattering and chlorophyll-a. This data collected routinely by the Seacat (15 minute samples) was recorded internally and also sent through the coil-cord to the surface buoy for telemetry to shore. The first deployment in the winter 2005-06 (mid-December through February) worked well. The coil-cord and tether showed no wear, or signs of failure. It was cleaned and redeployed again on 30 March and retrieved mid-July 2006 after the telemetry up the coil cord-cord stopping sending signals. The post-deployment evaluation of the mooring is ongoing. The telemetry stopped when the Seacat battery prematurely ran down. A similar Seacat with identical sensors ran for the full 3.5-month deployment. While the conductors were still in intact, first indications are that the cable was flooded (lower resistance between conductors) through a rope strength member. There was no visible mechanical damage to the rubber tether and coil-cord assembly. We hope to improve coil-cord cable design to prevent flooding and conductor wetting in the future. If this proves successful, the high-stretch conductive mooring element will be a viable candidate for powering sensors down the cable (lowering underwater instrumentation costs by not having to provide power in the sensor) and recording data that is telemetered up the wire to the buoy (again reducing underwater instrumentation costs by not having to store the data). This will enable the buoy to then telemeter the data collected from depths to shore with other information/data collected on the buoy. Also, the high-stretch conductive mooring element can be used for buoy-based observatories where the advantages of elastic compliance can be realized and data can be routinely telemetered to shore for distribution on the Web