Using SES technology, a new daughter craft will provide similar operational performance as larger CTVs, but with improved fuel consumption
With windfarms moving further offshore into harsher environments, crew transfer vessels (CTVs) will need to provide stable, fast and fuel-efficient platforms for safe, reliable operations. An independent Norwegian ship designer believes it has struck on the ideal solution in the form of a first-of-a-kind surface effect ship (SES) daughter craft.
Delivered in 2018 to WindPartner, the 15-m SES daughter craft Sea Puffin 1 logged extensive test and demonstration experience at North Sea windfarms Horns Rev 1 and 2 and Hywind Scotland last year, until the outbreak of Covid-19 halted the programme, ESNA naval architect Trygve Halvorsen Espeland tells OSJ.
As a first of a kind, Mr Espeland admits the vessel had its “share of child diseases”.
However, he points out, Sea Puffin 1 has “repeatedly confirmed that she meets and exceeds all performance expectations for speed, operational wave height and fuel consumption.”
He says SES technology provides high performance in a small vessel. Sea Puffin 1 uses its air cushion for motion damping when accessing wind turbines, offering the same wave height for safe transfer as 20 to 22-m catamaran CTVs. When it comes to exposed windfarms such as Dogger Bank or those proposed on the US east coast, Sea Puffin 1 provides double the operational weather window – 70% as compared to 35% for a conventional daughter craft, according to Mr Espeland.
“Sea Puffin 1 provides double the operational weather window – 70% as compared to 35% for a conventional daughter craft”
Sea Puffin 1 performed safe turbine access in up to 1.8-m significant wave heights, and the motion-damping system is especially effective in the typical long wavelengths of the exposed windfarms.
Due to its small size, Sea Puffin 1 yields lower fuel consumption than other CTVs with similar performance. At full speed and performance, the consumption is 150 liters/hour. In mixed operation of push-on and transit, the vessel has recorded average operational consumption of 100 liters/hour.
While feedback on its performance has been positive, it is clear that Sea Puffin 1 is a small vessel where several design choices were made to save weight to allow single-hook davit operation.
These were addressed in the development of a Mk II version of the vessel, Sea Puffin Mk II, which will offer “a step up from Sea Puffin 1, with a revised design and weight optimisation,” says Mr Espeland. Among the changes are a larger cargo deck fore and aft, more space and improved views for passengers, reduced noise and increased luggage storage. Additionally, the Offshore Launch and Recovery Systems (LARS) will be offered as single-hook, dual-hook or cradle solutions.
Mr Espeland sees further refinements ahead, driven by charterers’ increased appetites for hybrid and electric propulsion to reduce fuel consumption and cut emissions.
ESNA has developed a zero-emission battery solution that can offer around two hours of operation between charging. “With a daughter craft, the charging can be easily supported by the mothership/platform with the LARS system,” he says.
The biggest challenges of such technology will be cost and charterers’ willingness to pay for it. Mr Espeland, however, thinks that this will change based on the vessel’s opex, expanded operating window and environmental performance. “We are optimistic that [reduced emissions] will be more valued in future tenders
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