Hybrids: More than a change in the engine room
Andy Page of naval architecture consultancy Chartwell talks to Stevie Knight about the challenges and rewards that hybridization will bring to commercial marine.
Founder and MD Andy Page, known for his work with Alicat, set up Chartwell around a year ago. He explained that in response to the broadening market demand the company has developed not just one, but two hybrid vessel variants.
The first is the brand-new Chasewell monohull, aimed mainly at the pilot and patrol boat market: the initial model is a 9m model presently under build at Wight Shipyard, although there are 11m, 14m, 15m and 18m designs with the potential for scaling up even further.
Inside, the propulsion is a reasonably straightforward parallel hybrid, engaged by a clutch. “This leaves the mechanical drive train intact, giving traditional maritime pilots the comfort of knowing there’s extra redundancy and that the propeller is directly coupled to the shaft,” said Page.
However, electric operation typically gives you sub-8 knot speeds - and this has particular consequences for the hull design he explained: “The effects of slow speed drag haven’t been of much interest to the industry. Generally, we’ve been far more focused on what it takes to bring a boat up to hump speed – not so much about what happens on the way to that point.”
Getting it right has been tricky, he admitted: “We wanted to lower water resistance and the electric power range, but we had to be cautious not to increase drag at higher speeds as a result.” So, the Chartwell team generated three different hull forms, using CFD analysis to explore the concepts till they finally found a shape that hit all the right buttons: “It has a relatively deep forefoot at the bow, but a reduced wet area aft”, explained Page.
By contrast, Chartwell’s other hybrid development has been twin-hulled vessel; while both have batteries, this is an entirely different animal as it will be a series, not parallel, design.
The first of these is destined for US research: a 20m catamaran with a relatively shallow 1.2m draft which will be used to gather sediment samples, take bathymetry readings and carry out fish, bird and mammal studies. “Here the electric motor is directly coupled to the drive shaft as it will spend a huge amount of time at slow speeds - for example on an S-pattern survey path,” said Page.
It will be plugged in overnight to recharge, giving enough battery power to go without switching on the gensets for at least a few hours and that means silent running for collecting fish, wildlife spotting or picking up shallow water samples. As Page pointed out, there’s more to performance than the fuel bill: “When I say this boat is efficient, I don’t just mean the rate it burns diesel – it also helps those onboard to work effectively in their various roles.”
The pilot, patrol and research segments may be the new company’s initial entry, but Page predicts these won’t be the last. Hybridisation offers important advantages to wind support ships which often spend half their day loitering. More, he believes that motivated by organisations like the Carbon Trust and other European accelerator programmes, systems will evolve to allow vessels to pick up a charge from the power generated on site.
However, he underlined that alternative power, especially the series hybrid configuration, stands to break through some of the longstanding barriers to innovative crew transfer design.
“A diesel-electric drive gives you more flexibility. If you start to look at SWATH forms, you haven’t got much volume where the shaft would be and it makes for an awkward layout. But with a series hybrid you don’t have to try to find room for it – it’s connected by cables instead,” he said, and added: “It gives the naval architect a lot of options for smart design.”
Lastly, he pointed out that the interest is rising: “Local authorities and councils are taking an active role now - they are actively looking for local emission reduction in their harbour craft.”
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