Thoughts on Electric or Hybrid Drives

Open any number of yachting magazines, and you’ll come across mention of electrical and hybrid drives. More than a fad, these propulsion ideas offer some distinct advantages. New technology excites me but, it’s best to thoroughly understand just what you are stepping into before slashing out for the substantial cost.

Hybrid drives follow their vehicular EV counterparts. Mix up a traditional internal combustion power source with an electrical one. Individual torque and power characteristics are matched, providing a power profile that is not otherwise achievable. A good example application would be a harbor tug that spends its life operating at 10% full-power tootling about the place then uses everything for short bursts when required. Adding an electric trolling option and battery bank allows the diesel to be run intermittently at a moderate load to charge the batteries, then turned off until needed for towing or pushing. It’s more fuel-efficient, less harmful to the engines, and a lot fewer emissions overall. 

You can implement hybrid drives in Series or Parallel. Series uses diesel generators and a battery bank with electric motors coupled directly to the props. Parallel uses diesel, electric, or both to drive the props. Parallel provides greater redundancy and is a lesser step away from traditional motor yacht practice. With half an eye on resale in a traditionally conservative market, we choose a parallel Hybrid drive technology.  

Electric, Serial Hybrid and Parallel Hybrid Drives – credit Praxisautomation.com

We spoke with five manufacturers in all. Marine Hybrid, Esco, Praxis, Transfluid, TEMA. Each had products suitable for use in parallel with our relatively slow-running John Deere diesel engines. We wanted to drive the hybrid either from a large battery bank or drive two props from one diesel engine (significantly reducing engine hours). As the battery’s power density is nowhere near that for diesel fuel, the operating envelope was to be trolling or maneuvering, all slow speed operations. We also now have electrical storage for extended silent time at anchor. Vanguard needs little power at that speed, perhaps 20kW or so. Thus the hybrid motor size was dictated by the need to charge the batteries rapidly. It was not a consideration of the need to power the vessel itself.    

We also have much more powerful installation for not “if” but “when” Electric Vehicle development creates batteries with better power density.  We can discuss more in the hybrid drive in a later blog. For now, let us sum the advantages as we see them. 

  1. Silent running in environmentally sensitive areas or when using DP for station keeping at night (e.g., head to wind to minimize rolling at anchor).

  2. Removal of both the main and standby diesel generators and supporting systems – more engine room space.

  3. True dynamic positioning. Almost instant torque availability and quick direction shifting. This provides an effective “virtual anchoring capability,” greatly assisting maneuvering and docking short-handed. An 80-foot yacht is a handful to dock on your own by other means.

  4. Minimizing engine running hours, we can drive two props from a single-engine at a good load factor rather than run both.

  5. Almost excessive drive redundancy.

Do we truly need such a system? Almost certainly not. Do we want to play with the technology and go through the mind games of understanding and specifying what will be a very flexible system? Frankly, it is our party, so yes, we get that opportunity this time around.  Will a new technology distract from the value of Vanguard? I don’t think so as it can be extracted, leaving the traditional diesel engine propulsion in place undisturbed. 

One last thought, I’m a Star Trek fan and can now say to my young son”. No 1 – engage hybrids and take us out of here!”. hooooorahhh!

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