Traq-ing underwater trenching

Hi-Traq streamlined chassis with buoyancy grabs and tooling cylinder.

Cable-laying challenges on offshore wind farms has led to a new tracked trenching vehicle being designed, which may also have benefits in the oil and gas sector. Chris Jones explains.

Unlike the calm subsea environments in deepwater locations, the waters around offshore wind farms are susceptible to strong currents and wave action.

These conditions lead to changes in the underwater landscape, creating up to 20m high sand waves and ripples on the seabed. Potentially uneven seabeds range from loose sands through to extremely hard clays, which require different trenching tooling for cable burial operations. High wave loadings and strong cur- rents can create up to 6knot combined water velocities, requiring a minimum submerged vehicle weight, in order to keep a vehicle on-station during operations.

Many of the more conventional, neutrally buoyant, free swimming ROV’s have difficulty coping with these demanding environments and can lose position; endangering the cable being buried.

IHC Engineering Business saw an opportunity to create a new solution to make traversing these rough terrains easier by using a tracked vehicle. The Hi-Traq subsea crawler is designed to stay on station in challenging conditions, increasing available operational windows and safety.

With support from the European Regional Development Fund, Hi-Traq has been developed by northeast England-based IHC Engineering Business, part of Netherlands-based IHC Merwede, over two years. It is a remotely-operated, tracked, trenching vehicle, designed for power cable burial on offshore wind farms. A Hi-Traq demonstration vehicle underwent land-based proving trials earlier this year at IHC EB&rsquo s Port of Tyne testing facility. The testing encompassed a range of activities, from 20° incline traverse trenching to 10m-radius trenching with skid, wagon, and crab steering tests. Hi-Traq has a four-track undercarriage system with a bogey arrangement. The design means the vehicle has low ground-bearing pressures, because it evenly dis- tributes the weight of the vehicle, enabling maneuvers over variable terrain to be managed, while providing high traction, compared to two-track alternatives.

The Hi-Traq demonstration vehicle during land based trials.

The vehicle has an automatic self-levelling system, allowing it to traverse 20° sand wave and ripple slopes and maintain a constantly level chassis to ensure stable and vertical trench depth.

Independent track steering reduces the traction loss associated with skid steering, preventing the trencher from getting “bogged down, and enabling a 10m radius corner trenching capability. This means cables can be trenched up to the wind turbine foundations, avoiding the need to deploy additional support vessels, which are usually required for external protection measures, such as matressing or rock-dumping.

The undercarriage system has two trenching modes; jet sword cutting, for softer soil conditions, and mechanical cutting, using cutter chains, for trenching through harder seabeds.

The system was primarily designed for cable on offshore wind farms.

For this purpose, two chassis configurations were designed, a 25-tonne (in air) unit, with jet swords only, and a second, weighing 50-tonne, with both jetting and mechanical cutting options.

IHC Merwede also sees the potential for Hi-Traq to be used in offshore oil and gas, so a third design weighing 65-tonne in air was created. The larger system has been designed to handle larger product diameters, such as oil and gas flowlines and flexible pipelines, of up to 400mm in outer diameter. This vehicle’s functionality compares with a previous IHC Merwede trenching vehicle i-Trencher but the Hi-Traq system is 30 tonnes lighter.

Track pivoting on the Hi-Traq demonstrator vehicle.

EB designed and built the i-Trencher system, including a 1.25MW trenching vehicle, its launch and recovery system, and heave compensation system for trenching and backfilling up to 2m deep in hard soil and deep waters.

Hi-Traq has an operator control system with surveillance and locating technology, which enables operations to be viewed remotely using a universal fiber optic multiplexer system. A launch and recovery spread has been designed to be suitable for deployment in high sea states, with a snubber system designed to manage dynamic loads caused by wave action. The offshore renewables-focused Hi-Traq vehicles can be deployed using a lift umbilical.

IHC Merwede is planning to extend Hi-Traq’s tooling range to address the inspection, repair, and maintenance, segments, as well as decommissioning. Hi-Traq could also carry other subsea tooling, such as an educator dredging system, coupled to a long-reach excavation linkage, to carry out subsea dredging.

Chris Jones is responsible for product development of subsea excavation and trenching equipment at IHC Engineering Business. He primarily works with product focused research and design whilst developing close contact with the market place to define product development requirements. He was previously at Caterpillar Building Construction Products, aiding in the development of market hydraulic excavators. He studied at the University of Central Lancashire.

IHC Engineering Business is part of IHC Merwede, which supplies vessels, equipment and services to the dredging, mining, offshore and marine markets.