Couplings and dampers can combine to protect a drivetrain, reducing maintenance, extending a vessel’s life and improving the wellbeing of crew
Couplings and dampers have a multi-functional role to play in a ship, protecting vital powertrain components, reducing hull-borne noise, improving the comfort and wellbeing of crew and protecting the sustainability of ocean life.
And, as explained by panelists at a recent Riviera Maritime Media webinar, the gains from these increasingly advanced technologies fall straight to the bottom line through reduced maintenance costs and extended vessel life.
However, it is vital that the technology in couplings and dampers – or mountings – is precisely integrated so that each operate to their mutual advantage.
Part of Marine Propulsion Webinar Week, the webinar event, entitled Couplings and dampers: Protecting your power train, was produced by Riviera and sponsored by Geislinger Powertrain Solutions. The webinar panellists were Dr Klaus Prenninger, manager of torsional vibration calculations at Geislinger Powertrain Solutions, and Matthew Coombs, manager North American operations for mountings specialist Christie & Grey.
Dr Prenninger explained that Geislinger develops tailor-made couplings in a multi-stage process. First, it builds a torsional model that figures out the stresses in the crankshaft, gearbox and the shaft line. “Then, depending on the needs, we put in, for example, torsional vibration dampers in the front of the engine, torsional elastic couplings and misalignment couplings and carbon shaft,” he said.
Throughout the process, Geislinger uses proprietary software. In an average year the group performs more than 500 operational calculations for many different applications and conditions. Throughout, the aim is to achieve a lightweight, extremely robust and compact solution.
“Reduced vibration makes the vessel more efficient and extends its life”
In a highly collaborative arrangement, Geislinger and anti-vibration technology provider Christie & Grey work closely on marrying the former’s coupling with the latter’s mounting system.
As Mr Coombs added, there are several reasons for this: first, an effective mounting system improves the quality of life for everybody onboard by reducing vibration. In support he cites the way that improved damping technology has dramatically improved noise levels, down to around 65 decibels. This compares with levels of 80 to 90 decibels a few decades ago that could permanently damage hearing.
Second, it helps protect sea life by dissipating underwater sound – an increasingly important function as ecological regulations become tougher.
And third, reduced vibration makes the vessel more efficient and extends its life.
Mr Coombs explained: “Klaus works on the torsional end of the project and we work on reducing the noise in the structure. It is very important that we interact to make sure the systems perform best.”
For its part, Christie & Grey ensures the system operates with six degrees of freedom. “Those six degrees of freedom cover the frequency range that the customer specifies,” Mr Coombs explained. “These solutions are not something you buy off the shelf.”
A wide variety of factors are included in the calculations for the mounting, such as the ship’s future working environment, likely sea states, and how the vessel will be used. “We want to isolate those things from the driveline. We want that engine to be pristine. A quiet ship functions best,” said Mr Coombs.
In one of many successful solutions, the 100-year-old company was able to fix a severe cavitation issue with a ferry boat that was caused by the propellers. “Because we were able to isolate it properly, we were able to block the vibrations from the shaft,” he said.
An additional advantage of well-mounted, vibration-isolating systems is that they last longer. “It is not unusual for our vessels to go 20 years on a single set of isolators,” said Mr Coombs. “Service life is everything. What does it cost to replace a mounting system? It’s very expensive. What does it cost to align a system? Also, very expensive.”
Carbon fibre shafting
Both panelists are excited about the potential in carbon fibre shafting, particularly for its ability to achieve less noise – softness – in all directions rather than just vertically. Also, as Dr Prenninger pointed out, new developments in carbon fibre shafts make them suitable for the reduction of high-frequency vibrations. They are usually mounted between the gearbox and propeller.
The panelists stressed the importance of engaging expert advice whenever engines are changed or re-rated, or when propellers or other essential elements of the drivetrain are altered. Any of these can introduce harmful resonances in the propulsion system.
“If you’re changing anything with a coupling, and you have an isolated engine, you better be talking to your isolation manufacturer, your engine mount manufacturer,” said Mr Coombs. “That is because everything that happens in the driveline is based on natural frequencies and those natural frequencies will affect the mounting system, or could potentially affect that system. So that should be recalculated and we should be validating any selections that are currently on the engine and making sure that is going to be a clean system.”
Both men stressed the importance of installing the highest-quality couplings and dampers from the very start, if only because of the high cost of rectifying problems later. “You just have to do the job properly and invest in quality products,” said Mr Coombs. “An alignment costs US$10,000; if you have to do that four times in the life of the vessel, what does that amount to? When you compare it against US$3,000 per set of isolators, you just saved US$20,000 or so.”
But in the case of new vessels, Christie & Grey has found that shipowners benefit substantially when mounting systems are designed into the ship from the outset. “It will pay back royally in reduced maintenance,” said Mr Coombs.
It is also vital to design an easily maintained system. “Well designed systems are cost effective. They’re designed to be maintained. They’re designed to be easily serviced. They’re designed to last a long time,” he concluded.
Dr Prenninger noted how couplings and mountings are increasingly purpose-designed for more complex propulsion systems. For instance, power is transferred from the engine to generators. A wide variety of propellers with zero or full pitch must be controlled, depending on engine speed. “Finding templates and couplings to protect all of these different factors is getting more complex,” he said.
Weighing in on the complexities posed by variable speed, Mr Coombs said it was vital to understand the whole range of speeds and how it affects coupling and damping systems through the entire range.
And sometimes it is just not possible to cover every situation. “[It] may be in a variable speed application that you have to avoid certain rpm,” he said. “There is no way around it. You try to find a natural frequency that has the least effect. You focus on that and you let that be the dominant factor, [but] creating completely clean systems is very, very difficult.”
On the effects of ambient temperature on mountings, Mr Coombs said his own experience suggested it was not usual to see high-risk increases in temperatures because mounting systems are normally located low down in the bilge. It is important however to have good airflow.
On the same issue Dr Prenninger said Geislinger typically asks the customer about the type of engine oil that will be used and then includes likely temperatures and viscosity among other factors in its calculations.