Next generation CTVs arrive to help combat emissions

Reduced emissions and fuel consumption, increased speeds and range, and an ability to operate in higher sea states are factors influencing the design of the latest crew transfer vessels (CTVs) for the offshore renewables sector.

Vessels are being designed with hybrid propulsion, electric drives and an ability to operate in more remote locations for longer, as the offshore wind sector installs deepwater fixed and floating turbines.

Global Marine Group subsidiary CWind head of fleet Lea Hurst explained the latest trends in vessel design during Riviera Maritime Media’s Maritime Hybrid, Electric and Hydrogen Fuel Cells Conference in Bergen, Norway, in October.

“We are at a pivotal point in the success story of offshore wind,” he said. “As we continue to scale up, we are looking for solutions to industry challenges to reduce emissions, reduce costs and increase performance of offshore assets.”​

Challenges in reducing emissions and costs can be overcome through investment in hybrid propulsion and batteries for low, or even zero, carbon operations. If these are not viable, then vessels should have IMO Tier III-compliant engines for minimal NOx and particulate matter emissions.

“Reflecting on what our customers now require of us, we must strive to create vessels which are future-proofed and ready to adapt and evolve to the changing demands of the industry,” said Mr Hurst.

“A vessel which can perform in increased sea states is vital for reducing lost time due to weather days. As projects move further offshore, the investment in individual vessels increases,” he said. Capital investment in CTVs of more than 30 m in length are estimated to be around US$10M.

Earlier generations of CTVs were built to operate in 1.5 m significant wave height, but there are requirements for up to 2 m height. “This is becoming more of a desired advantage for projects further from shore,” said Mr Hurst, as is having accommodation, including sleeping areas on vessels.

There is also an advantage for increasing passenger capacity. “The sweet spot seems to be 24 passengers; however, some of the largest CTVs in the market are able to carry up to 56,” said Mr Hurst.

“Clients are seeking flexibility for a high cargo capacity to ensure they have the ability to utilise their contracted vessel for as much work as possible,” he said.

“We must create vessels which are ready to evolve to the changing demands of the industry”

The hullform of CTVs has also become important for operational and environmental performance, capacity and range. “The impact vessel hullform has on emission reductions is now being realised,” he explained. “It is not enough to simply choose the vessel based on aesthetics alone, we also must evaluate the operational profile requirements of the work it is required to do on site.”

Most hullforms on existing CTVs are monohull or catamaran. There are also trimaran, swath and surface-effect ship (SES) hulls. The benefits of monohulls include ride comfort and fuel saving, while catamarans have larger fore decks and better stability.

Trimarans provide stability and larger cargo capacity, while swath have better ride comfort and SES offer higher speed and ride comfort.

CWind is set to introduce the world’s first hybrid CTV with an SES hullform, CWind Pioneer, which has the “ability to be zero-emissions in-field, whilst the technicians are on the turbines, as well as being 20-30% more fuel efficient than a conventional crew transfer vessel,” said Mr Hurst.

“The vessel marks the next generation of CTVs, capable of transferring in increased sea states, reaching speeds exceeding 40 knots and tracking a wealth of data to increase performance, all whilst offering a reduction in emissions,” he explained.

“This vessel offers customers a more cost effective, greener alternative to expensive, fuel-intensive SOVs, which is especially beneficial for windfarms located further from shore,” he said.