It all comes down to control

A group of companies has undertaken "mapping" the kinds of loads and capacities found on hybrid marine installations – and how they play off each other. No small task.

Hymar is an EU supported R&D venture that aims to deliver an "architecture" for state-of-the-art marine hybrid systems for displacement vessels up to around 24m in length. Now, this should give some outlines around what make a design work – independent of the actual supplier of the individual bits of kit – and according to project leader Ken Wittamore, it will also be equally applicable to parallel or series drives.

Its got a big remit: to deliver more fuel efficient and sustainable propulsion and power options for small craft, to deliver systems which satisfy the market demand for increasing amounts of electrical power on board and to reduce the environmental impact of small craft by cutting down both fuel consumption and noise and vibration.

Energy questions
Mr Wittamore explains it’s a complicated area. When you just have a standard diesel driving the propeller shaft, you have just the one fuel conversion – from diesel to the shaft.

“With a hybrid, you have many more, you go from diesel to generator, to electricity, to battery to motor and shaft. On every changeover you accrue losses. So, at first sight it looks impossible to balance the equation in favour of hybrid - you’d think a diesel is always going to be better,” he explains.

But, what a hybrid allows you to do is operate all the bits of kit at their most efficient load points. As it turns out, a diesel engine directly onto the shaft isn’t actually the most efficient: if you are involved at low speed, low power manoeuvres. The data we are getting shows hybrids are actually more efficient in this area. But, it’s not easy to qualify what kind of set up is best as it really depends on what the systems are going to be used for.

Efficiency mapping
The secret lies in knowing the characteristics of all of the key components, particularly their efficiency maps, and then ensuring that they are only used when they can run at their optimum point.

For example, in parallel systems, if only the generator is being driven by the main engine it won’t absorb all the power the diesel can produce – which leads to inefficiency. But if you are using the diesel to both drive the shaft and charge the batteries, then it can becomevery efficient.

The important part for all of this is you quickly find you need an intelligent "brain" which understands all of these complex interactions and can make decisions based on the user’s objectives, which may not just be about fuel efficiency. He may want to sail faster, or run quietly, or minimise wear and tear on the boat.

So with a parallel drive for example, the control system knows the batteries charge and the prop runs happily, both together, at say 6 knots: but then if you drop the speed it will know that there’s no point in running the diesel, and it tells the power management system its time to cut that out and start to pull the power from the batteries. “The brains, the ‘intelligence’, is actually to do with the control strategy itself,” says Mr Wittamore. “One stage back from the actual power shunting.”

This needs computing power. “We are using a custom designed controller and the Android operating system to give us maximum flexibility and transparency. You can get information about how the boat is operating anywhere on the boat including on your mobile or on your notebook – it will be fully accessible by the new-generation technology."

Power switching
Steyr adds that its collaboration with Mastervolt is a particular benefit, because one of the most crucial elements of the whole hybrid installation is, after all, switching over the power.

Nick Hamilton of Mastervolt, which is working with both parallel and series hybrids explains,:“There’s some clever stuff inside these engines, it is sophisticated engineering. However getting the whole system to work together – and reliably - is actually quite difficult.”

The power management system has to bring together the generator, charger, inverter and the electric propulsion motor. Its job is to effectively combine the energy sources, whether from the diesel engine, the battery pack or shore power when available - and use it for every possible combination of AC, DC, battery charging and propulsion – all at the most appropriate loads.

So controlling these energy flows has to be fully automatic - leaving no worries about peak demand. For instance when switching on air conditioning the modules will first draw the start up load from the batteries and subsequently automatically switch on the variable-speed generator and run it at the minimum speed required in order to minimise noise. When shore power comes available it will switch over to using that source without a glitch.

Added innovation
A load following, self-pitching propeller is part of the overall Hymar project: Adrian Miles at Bruntons explains that the Autoprop blades are designed to give a very broad performance, useful for ordinary sailing, but a definite advantage for hybrid applications which can give widely variable amounts of "push".

As the pressure is reduced on these blades, the more pitch is applied and vice versa. The result is maximum efficiency whatever the conditions, with increased speeds at lower engine revs and lower fuel consumption and emissions.

Another part of the Hymar project is a new generation of thin plate pure lead (TPPL) batteries from Enersys with optimised geometry and electrochemistry especially developed for hybrid applications. Further, it’s resulting in the development of new permanent magnet DC motors, generators and controllers that have been optimised for hybrid configurations.

Interested people will be able to get a good look at the results of the Hymar project at Icomia’s First Hybrid Marine Conference in Amsterdam, this November - immediately prior to the start of METS.