HYMAR project deepens its understanding of marine hybrid systems. Once again another year’s testing for the HYMAR project has come to an end. It was a very frustrating test season!

We decided to add a thrust meter to the propeller shaft on the boat. This is not something that can be bought off the shelf as thrust meters for rotating shafts basically don’t exist. It had to be built from scratch, and then calibrated for our application, and this is where we ran into trouble.

The device outputs a signal in milliamps (mA). This has to be converted into kilograms (kg) of thrust by multiplying the mA reading by an appropriate calibration factor. The accuracy of our results is totally dependent on the accuracy of the calibration factor. The meter was tested on the bench prior to installation in the boat to determine an appropriate calibration factor, but when we applied this to the test results we got in the boat the thrust numbers were clearly erroneous. I spent a good part of the summer devising various in-the-water calibration rigs and trying to figure out what was going on, but without getting results that I trusted. We got the propeller folks at Bruntons involved which is when we discovered that one of them – Dr Stephan Helma – is an expert in these kinds of things. With his help we got the meter sorted out.

The thrust meter enables us to measure propeller efficiency in real time and to see how it varies with changes in boat speed, wind and waves. It’s terrific data. We retested all the propellers we had tested the previous year, adding this information to our database. We had expected to complete this work in the early part of the summer and then convert to a hybrid system, but because of the delays with the thrust meter this did not happen. We will convert over the winter months and (hopefully) hit the water with a fully-functioning hybrid system next summer.

In the meantime, as I mentioned in my last blog, Homewood Products Corporation built a prototype generator based on the optimized design criteria we developed from the first year’s testing. This generator was shipped to Steyr Motors (a HYMAR partner) and run through its paces. First, the Steyr engine which was used to power the generator was tested and a ‘fuel map’ created for its full speed and power range. Then the generator itself was tested for its efficiency across its full speed and power range. Finally, the engine and generator were married together and tested for efficiency across their combined speed and power range.

The generator tested out exactly as we hoped it would. We have proved that it is possible to design and build a generator for marine hybrid applications that can be operated over a fairly broad power range at close to peak efficiency 100% of the time. This information is being integrated with the testing being conducted by EnerSys on the HYMAR project’s Thin Plate Pure Lead (TPPL) ‘Odyssey’ batteries. The goal here is to derive battery management and charging algorithms that will optimize battery life without operating the generator outside of the peak efficiency enveloppe.

Meantime Mastervolt, another HYMAR partner, has been developing suitable power conversion equipment (inverters, chargers, and DC-to-DC converters) for the project with an interface to the NMEA 2000 communications bus. Bruntons and INSEAN, an Italian marine research institute, have been working on an optimized self-pitching propeller.

In the next phase of the project we will investigate electric propulsion motor efficiency factors over a broad range of operating conditions, and the interaction of electric propulsion motors with propellers. This is the last major set of information that we need to design and specify optimized hybrid systems. As the data emerges it will be integrated into the system controller that is under development. By the end of the 2011 test season we should have achieved our goal of creating an optimized hybrid system, and of being able to quantify when, and by how much, it is more efficient than an optimized conventional system (and also when, and by how much, it is less efficient).

This is, of course, assuming that things work somewhat more as planned than they did this year!