Class societies have launched a raft of notations related to underwater noise and vibration – while there has been a slow take-up from ship operators, this may soon change with incentives and benefits to encourage adoption
Interest in reducing underwater noise has cranked up – but in order to capture more interest from shipowners, initiatives have recently been launched, including one from Bureau Veritas (BV).
BV introduced its class notation NR 614 – URN in 2014 and updated it in 2016. BV launched this voluntary notation to help ship operators and shipbuilders measure and reduce underwater-radiated noise.
RINA Services launched a voluntary notation last year to be applied to commercial vessels that have mitigated underwater noise. Its Dolphin notation was developed for vessel operators which operate in sensitive marine areas and who want to demonstrate they have acted to mitigate the impact of their vessels.
And ABS and Lloyd’s Register have followed in their footsteps this year by launching their own voluntary notations in this sector. DNV-GL has its Silent notation.
To make the notation more attractive to shipowners, in July BV updated its rules to include another measurement procedure for adding the notation to the vessel. BV head of measurement department Eric Baudin explained the measuring procedure has been shortened from two passages by the ship including two u-turns and realignments, to just one passage. This has been achieved by doubling the instruments used to measure underwater noise and vibration.
Mr Baudin said “After continuous exchanges with stakeholders, we have introduced a new underwater noise measurement procedure in line with ship-in-service constraints. The expertise of BV specialists and their key partners answered this need with a cost-efficient solution that still sustains the level of accuracy. This procedure means it is less expensive (in terms of fuel and time spent) for the shipowner.
“This was particularly aimed at ships in service for which we have less flexibility than for new delivered ships during sea trials.”
While there is interest in the underwater notation and BV is seeing “more and more requests”, the uptake among ship operators has been slow. BV’s notation is currently being used by a fishing research vessel. To increase shipowners using the notation, “we are trying to listen more carefully to the market, put efforts into informing the stakeholders and find ways to promote the notation.”
Another problem is the reluctance of some shipyards to follow the notation. Mr Baudin explained “Some shipyards are not fully aware of what could be done to fulfil the notation so are afraid to accept the specification.”
He explained that measuring and reducing underwater noise has a cost, which means it had not previously been a focus for ship operators. But Mr Baudin is keen to address this. “Dealing with underwater noise and vibration is not solely one initial cost, it is linked to the rest of the ship and design and is part of the overall noise and vibration management. If you do it properly you can address underwater noise and vibration at the start and boost comfort, and propeller efficiency is increased if a design is worked upon; that reduces underwater noise and vibration as well. The return on investment is thus obvious.”
Mr Baudin said it was a good sign that both ABS and LR had released notations. “The trend is promising, as more class societies are considering this an important issue and shipowners are more and more aware of this.”
He singled out another reason that would push the uptake of such notations: Two Canadian ports, Port of Vancouver and Prince Rupert launched port tax reductions of 47% and 50% respectively last year to reduce underwater noise due to the endangered species off the coast of British Columbia.
Mr Baudin commented “Regarding global actions Canada is still very active and during last MEPC session in IMO [in Apri 2018] a lot [much more than expected] of flag representatives showed their interest in this underwater noise topic. There have been new discussions and actions are in progress to carry on working in the direction of improving knowledge, sharing feedback and tackling this issue at the lowest cost possible.”
Eric Baudin (BV): Advice to ship operators
Noise and vibrations were one of the top items on the agenda for Shipyard De Hoop when it came to building Lüftner Cruises’ new Amadeus Queen – the 15th river cruise vessel the shipyard has delivered to the river cruise operator.
The vessel is now in service following its naming ceremony on 4 April 2018.
Two Caterpillar 3508 main engines, rated at 783 kW @ 1,600 rpm, directly drive two Veth Z-drives with contra-rotating propellers. These main thrusters are recessed, limiting the minimum operational draught to only 1.52 m allowing the vessel to cruise most European rivers where water depths are often critical.
To isolate vibrations from the propulsion units, a double hardwearing flexible mounting system has been applied. On both sides, the azimuthing thrusters are mounted on separated bottom sections, which are integrated in a frame of the actual ship’s bottom. Furthermore, the main engines are mounted on double-vibration dampers and paired to the thruster units through flexible couplings. This so-called ‘boat-in-boat’ solution has the effect of reducing the sound levels in the public spaces and guest cabins.
To further reduce the sound and vibrations in the Amadeus club and pool above, another innovation was introduced: to lower the impact of propeller blade impulses to the hull, an air curtain buffer was installed – by blowing air in between the propeller and hull, the pressure pulses are not transmitted to the hull.
Incat Crowther has launched Spirit of the Wild for Gordon River Cruises – which it claims is the first tour vessel in Australia to operate in World Heritage-listed wilderness with silent drive.
Built by Richardson Devine Marine, Spirit of the Wild is fitted with a pair of MTU 10V2000M72 main engines. Added to this is a hybrid electric system, consisting of a pair of ABB e-motors, driving hybrid-ready ZF gearboxes. Incat Crowther said particular attention was given to the mounting of the engines and gears to reduce the transmission of vibration and noise. The main engines’ modest rating is tailored to the local manning requirements. In open water, the vessel will use ‘boost’ mode from the hybrid system, which matches motor speed to engine speed to add electric power. In this mode, the vessel operates at 25 knots.
When the tour vessel comes to the World Heritage-listed Gordon River, silent drive mode is engaged. In this mode, the main engines are shut down and the vessel runs on electric power.
Engine ventilation systems and the engineroom were addressed with a fully-engineered acoustic insulation system. Attention was paid to fittings and door openings, with seals and bushes used extensively to stop rattles and gaps. Incat Crowther said “In silent drive mode, the experience is eerily quiet, with seats returning sound level readings as low as 45 dbA.”