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Case study

Shallow water site investigation for offshore wind

Client: PDE Offshore

December 6, 2021

From the topside to the underwater instruments, our goal is to make offshore operations easier and less time-consuming, but also highly accurate. As PDE Offshore discovered, with Mini-Ranger 2, our 6G hardware and our Wideband 2 digital acoustic technology onboard, safe and efficient shallow-water site investigation operations, from tracking towfish to positioning seabed geotechnical equipment, are assured.

The challenge

In a short period of time, Taiwan has quickly become a leader in the global build-out of offshore wind. Starting from scratch in 2018, the country has been quick to ramp up its offshore wind capability. Taiwanese company PDE Offshore, based in New Taipei City, was quick to get involved in this new industry and came to us for a USBL system to underpin its offshore wind geotechnical site investigation service offering.

Specifically, it was looking for a system to support geotechnical site and soil investigation works for a new offshore wind farm in the shallow water Taiwan Strait. This involves deploying geotechnical drilling equipment on the seabed at each planned turbine site in just 20 – 60 m water depth. The frame holding the equipment has to be positioned accurately to ensure it’s aligned with the drill string deployed from PDE Offshore’s geotechnical survey vessel.

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Mini-Ranger 2 USBL

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The solution

PDE Offshore chose a combination of our Mini-Ranger 2 USBL system and our Wideband Sub-Mini 6+ (WSM 6+) transponder/responders to track and position their drilling frame on the seabed. Mini-Ranger 2 is built around the same market-leading 6G hardware and Wideband 2 digital acoustic technology you’ll find in our entire family of USBL systems – even the software is the same.

Critically, it’s designed to easily handle just the kind of shallow waters PDE Offshore had to work in on the project in the Taiwan Strait. At the heart of Mini-Ranger 2 is our HPT 3000, a highly capable surface-deployed USBL transceiver that’s optimised for high performance in shallow water, as well as high elevation and long lay back operating scenarios and data telemetry.

It was a simple choice for PDE Offshore, not least as their onboard surveyor was already familiar with Mini-Ranger 2. What’s more, it’s also a great option for smaller vessels and even unmanned surface vessels (USVs).

A wide range of Sonardyne 6G transponders can be used with Mini-Ranger 2, allowing you to select the most appropriate took for each task. For its operations in the Taiwan Strait, PDE Offshore chose our Wideband Sub-Mini 6+ (WSM 6+) transponder/responders. Designed for positioning ROVs, towfish and other mobile targets in water depths up to 4,000 m, WSM 6+ incorporates our Wideband signal technology, so it offers superior ranging accuracy and fast USBL position updates as well as full two-way Wideband support – interrogation and reply signals.

The results

PDE Offshore spent summer 2020 performing site investigation works from the MV Geo Energy in the Taiwan Strait. Our WSM 6+s were mounted on the seabed frame and tracked using the Mini-Ranger 2’s HPT 3000, which was deployed on an over-the-side deployment pole from the MV Geo Energy.

Huang Hsin-chih, president of PDE Offshore, says, “Where we work in the Taiwan Strait, water depth is from 20 to 60 meters; in the future, there might be a chance to work in offshore wind farm with water depth from 50 to 200 meters, so whilst we do need a very precise USBL, we don’t need one that’s full ocean depth capable. Through renting, we became familiar with Mini-Ranger 2 and the benefits it brought to our busy geotechnical operations. So it was a simple choice to decide to go ahead and purchase one of our own and it has proven fully capable for our needs on this and future offshore wind projects.”


Taiwan's offshore wind market

Targeting 27 GW by 2025

10-12 m/s average wind speed

60 m average water depth for each turbine

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