It started with two – superficially straightforward – renewal requests he explained: Gisaş Shipbuilding asked for harbour tugs that were both “lower emissions… and smaller” than its previous fleet, since the yard’s tugboats have to meet a rising environmental awareness along with a particularly tight operating environment inside the Port of Istanbul.
Unfortunately, these turned out to be conflicting demands: despite a growing utilisation of diesel-battery configurations for tugs and a number of clean-tech add-ons, NAVTEK’s initial R&D studies showed fulfilling the contract “wasn’t possible with hybrid or diesel power solutions”, he remarked.
That was when a young design engineer proposed a fully electric, rechargeable solution: “We all objected at first, but he convinced us to run a study,” remembered Acuner. Despite this, he added: “I confess that during the R&D, I’d been worried the final calculations would show that you couldn’t apply the technology to this type of vessel…” He shouldn’t have been concerned: although novel, the figures showed it was doable, and the NV-712 build got underway.
However, realising it took “meticulous engineering”. The main challenge was the sheer scale of the electrical power delivering the 32 tonne bollard pull: in fact, standard switching technology would result in “distribution panels needing more space than the whole ship”, he explained. Usefully, a heavy-duty crossover from the mining industry was found to power the 925kW propulsion motors driving the ABB thrusters below. This, combined with locating the various elements around the vessel and connecting them with single core cables rather than power bars, helped pull it all into the limited footprint offered by the modest, 18.7m long, 6.7m beam tugboat.
All this requires a substantially different developmental approach, said Acuner: he underlined that the most important lesson has been “don’t design a conventional diesel drive and then try to convert it…. but start from the very beginning as fully electric”. There were also some useful surprises surrounding predicted efficiency: “During the tests, we noticed that it needed less energy to complete an operation than we’d calculated,” he remarked.
Despite its success, Zeetug’s implications reach further than this first vessel, (which, he added, is “performing excellently” for Gisaş) or even the next three now on NAVTEK’s order book.
As Acuner noted, numbers of all-electric vessels are now rising, along with supporting technology: “Words such as ‘bunkering’, ‘fuel rate’ and ‘fuel treatment’ are being exchanged for ‘charging station’, ‘electric power unit price’ and ‘energy management software’,” he concluded.
As Gold Sponsors of the Coastlink 2020 Conference, take the opportunity to meet with the team from NAVTEK Naval Technologies Inc throughout the 2-day event. Book now to secure your delegate place at Coastlink. If you are a member of one of Coastlink’s supporting associations a 10% discount is available – please quote the Supporter code when making your booking and the discount will be applied. Alternatively, please call the team on +44 1329 825335 or email info@coastlink.co.uk.