SEDNA - Cable Burial and Maintenance System
Authors: Martelli Giorgio 
Published: October 2008

Abstract
The world is witnessing a high level of activity in the development of Submarine Cable projects, driven mostly by the voracious need for bandwidth of the Internet, multi-media and other communications. Fiber optic submarine cables are also expanding into the Oil & Gas sector, where existing satellite and microwave radio links are no longer sufficient to handle the high flow of data necessary to control and optimize production between offshore facilities and shore headquarters.
As the market continues to grow, it will attract more and more equipment suppliers and service providers; thereby, increasing competition. We believe that winning factors that will set apart leading companies from the rest, are the capacity to do more (performance) and better (reliability), and to provide a full, encompassing service so that telecom companies can concentrate on their business.
Two years ago, Sonsub started developing new technology for ROVs that has led to the Innovator-Work Class System for heavy work in ultra-deep water, having as a design goal the ability to deliver more power to the seabed in a more reliable way. SEDNA is the most sophisticated application of the INNOVATOR-technology, applied to the service of the subsea cable maintenance requirements.

Introduction
Sonsub conceived SEDNA as the ultimate flexible tool for maintenance for subsea cables. Sophisticated systems - both hardware and software - were implemented in order to give to the operator the capacity to use many different tools at various settings and even to re-configure parts of the system with a simple flip of a switch, or better a touch of a display screen. The first SEDNA vehicle is now work operational in Portland, OR under a 6-year contract to serve maintenance tasks to the subsea cables of the Pacific Ocean.

Design Basis and Main Features
The SEDNA design goals included the following challenging performance levels and task accomplishments.Trench at 800 m/h with a 1.5-m depth of burial.Trench in soils with undrained shear strength of 80 kPa with the standard jetting tool.Bury and de-bury cables in soils up to 150 kPa.Hold station while descending to depth in 6 knots of current.Perform a series of operations on either fiber optics or wire rigging cables, such as locating, gripping, cutting, attaching clamps, lifting and relocating.Perform various survey activities, of both cables and seabed features.Launch and Recover in sea states up to force 6 Beaufort.Rapid mobilization on a Vessel of Opportunity within 48 hours from call-out.
SEDNA achieves the above objectives by virtue of the following features.3,000 meters depth rating (extendible to 4,500 meters).500 shaft horsepower electro-hydraulic system powered by two 250 H.P. electric motors.Voltage/power transmission system of 4,500 volts.A 38.2 mm diameter umbilical with 67,000 kg break strength, double steel armor, rated for 700 H.P, employing ultra thin wall, high temperature power conductors with polymer technology.High thrust capacity: Longitudinal 3,000 kg, Vertical 1,100 kg.A single titanium pressure vessel to house all the electronic assemblies and subassemblies.Enhanced operator ergonomics surface consoles utilizing touch-screen technology and multiple picture-in-picture screens.