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Offshore Wind Journal

Next-generation CTV design would be efficient across the speed range

Wed 25 Jul 2018 by David Foxwell

Next-generation CTV design would be efficient across the speed range
The first example of Chartwell Marine’s innovative new designs could be in the water in early 2019

Crew transfer vessel design has mainly focused on achieving high speeds and good seakeeping while transporting windfarm technicians, but a British naval architect with experience in the sector believes there’s more to their efficient operation than that

Naval architect Andy Page, director of Chartwell Marine, has been designing crew transfer vessels (CTVs) for many years. With demand growing for ever more fuel-efficient vessels with reduced emissions in keeping with the offshore wind energy industry’s green credentials, he believes the time has come to refine CTV design and take advantage of new ‘hybrid’ fuel efficient, environmentally friendly propulsion technology.

Mr Page worked on CTVs at South Boats and Alicat Marine Design and on the design of a number of vessels for well-known owners. He has some interesting views about how viable hybrid propulsion for CTVs might be in practice, and the economic, environmental and operational case for hybrid CTVs, but believes it’s not just the propulsion system that counts.

Having worked at firms behind a good number of the operational CTVs in the UK and Europe, Mr Page launched Chartwell Marine when interest in new technology that can reduce emissions and fuel consumption, enhance operations and reduce maintenance needs of crew transfer vessels is growing.

A key example of this trend is the Carbon Trust’s Offshore Wind Accelerator's call for entries from companies and consortia interested in undertaking a study to evaluate potential technology for reducing emissions and fuel consumption.

“In order to implement these technologies, an understanding of the necessary infrastructure is required. The objective for the assessment part of the project is to understand the current and future technology applicable for offshore wind vessels, for example electric, hybrid-electric, liquefied natural gas, or hydrogen fuel cell hybrid-electric propelled vessels, and determine what their potential is for meeting the objectives,” said the OWA. The focus of the project is on CTVs during the operations and maintenance phase of an offshore windfarm.

Mr Page highlighted that regulation governing emissions is increasingly stringent, there is widespread adoption of emission control areas, and initiatives at ports and harbours to reduce emissions from vessels of all types that use their facilities.

He also highlighted that, until now, naval architects have rarely needed to study the effects of resistance on vessel performance at low speed. They have focused mainly, if not exclusively, on optimising CTVs for high-speed operation, such as when as in transit.

But that’s far from the whole story of a CTV’s operating profile. Mr Page said a typical CTV might actually only spend 20% of its time at high speed. A lot of the time – as much as 40% – it could actually be idle, spend around 20% of its time at less than 8 knots – such as when departing or entering a harbour – and 20% per of its operating profile pushing-on against a turbine for a transfer.

There are numerous potential options for hybrid vessels, including engines that can burn liqufied natural gas or hydrogen, or vessels that use batteries to store energy, but for hybrid designs making use of electric propulsion, “hull designs are inevitably going to need rethinking to create a boat that performs efficiently at all speeds and under both conventional and electrical propulsion,” Mr Page said.

At Seawork 2018 in Southampton in July, Chartwell Marine unveiled a new range of hybrid patrol/pilot boats, designed in collaboration with aluminium craft specialists, Wight Shipyard Co. The vessels are the first in the new Chasewell range and benefit from a hybrid system architecture and an innovative new hullform that minimises drag and resistance throughout the speed range.

The concept is equally applicable to CTVs, he told OWJ, noting that apart from propulsion innovations of the type the Carbon Trust is examining there are significant design challenges to be overcome in the development of effective hybrid workboats and CTVs. For instance, conventional hull designs, while appropriate for high-speed operation, may not be as suitable when a vessel is being driven at low speed by electrical propulsion alone, in order to reduce emissions.

The Chasewell range is the product of research undertaken by the team at Chartwell Marine into low-speed resistance, and benefits from a new hull design that enables efficient performance under diesel and electrical propulsion. “We’ve made some modifications to the hull shape that reduce drag at low speed,” he explained.

Ultimately this hullform, optimised through extensive computational flow dynamics testing, allows an operator to maximise time spent on electrical power, with substantial advantages when it comes to reducing total emissions.

“In today’s market, it’s rare that a one-size-fits-all approach will meet the needs of the end user,” said Mr Page. He envisages a CTV with a hybrid propulsion system and Chartwell’s new hullform might spend all of its time at low speed on electrical power, with very much reduced emissions, only using its diesel engines when more power is required, such as in transit.

The key thing about a CTV and many other classes of workboat is that a lot of their time is idle time when they are not under way at high speed, he concluded. “If you can eliminate the use of diesel engines during these periods you can reduce fuel consumption and emissions and reduce wear and tear on the engines at the same time. That means that you can increase the time between overhaul and reduce maintenance costs while benefiting from reduced emissions from hybrid propulsion.”

By early 2019 Mr Page hopes to have a demonstrator in the water that will be used to test the new hullform in diesel mode, after which it could be refitted with hybrid machinery.

 

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