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Serial Hybrid
"Only electric motors on shaft"
Full electric with range extending generators is a hybrid design that only has electric motors attached to the shaft. This is the greenest option as the operator can operate without the use of any fossil fuels. A large solar array will provide sufficient power for house needs as well as deliver excess power to the high voltage batteries. In practicle use, our yachts are sized so the owner can operate on electric alone for 1 day. While this may sound limiting, 85% of yacht trips are day trips. We understand the need for additional range which is what one or two generators will provide. Fuel tanks are sized to allow the owner similar range (~1 week) of runtime as an original diesel cat. At Nova Luxe we build superior cats to diesel and do not view electric yachts with limited range as viable products.
Additional information on this type of hybrid design can be found on the manufacturer Torqeedo's website.
The key points are summarized in the image below.
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Only electric motors propel the yacht. The power for these motors is stored in high voltage batteries built by BMW.
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Two propulsion battery banks ensure redundancy in the rare case of a battery fault.
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Power can enter the high voltage batteries from a variety of sources. Most commonly, shore power can re-fill the batteries in one night unlike Tesla's road charging infrastructure challenge. Marinas that service yachts of this size have 50a, 220 power available. Second, "always on" source of power are the solar panels. Solar panels provide power to the 24 volt house battery bank. The first use of solar is to cover all house needs. Next, when the house battery bank is full, a DC/DC multi-directional converter will send power to the high voltage batteries. Finally, the DC genset can provide power while underway giving our yachts the same functionality of the original diesel model.
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A large inverter provides AC power to the yacht and pulls from the house load as normal. Some of the house load is dedicated to navigation equipment for safety. If the house load runs low on power, then the bi-direction DC/DC convert will pull power from the high voltage batteries. At a minimum our yachts will have 80kW of power. A typical house in America uses 25kW of power in a day. In short this will provide ample power and prevent the need to run a generator at night.
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A few cloudy days can be ridden out and eventually the solar array will re-power the yacht.
Fully Redundant Blue Water Hybrid (INBOARD Electric, IE)
In this configuration we leave a diesel engine in one of the two hulls. We then modify the alternator on that engine for a significant increase in power generations. We expect this version of hybrid yacht to be more popular as it combines the old and known diesel technology with the newer electric motors. This design also allows for a higher top speed. A catamaran will run straight or with very little rudder adjustment on a single engine. Some catamarans, such as Aspen, are even designed to only have one engine. This model also allows for zero emission operation by using the electric motor. Again, it is sized so typical single day use can be all electric. Extended cruising can be done by using a combination of the electric and diesel motors. While it is possible to integrate the diesel and electric motor controls we choose to keep them separate for a fully redundant blue water system.
The hybrid design above has two major changes. One electric motor and both generators are removed from the system.
The diesel engine has a larger alternator attached and that alternator acts as the generator for the high voltage batteries. It will automatically power the high voltage batteries if low and the diesel is operating. Conversion costs for this model are lower as one engine compartment remains in a large part, unchanged.
Generators on yachts are no longer necessary. To find out more information on the system we use to pull more electric energy out of a diesel motor follow this Integrel Solutions Link.
An independent analysis on the merits of both hybrid designs was performed the DMS Naval Architects. For purposes of the analysis,
both designs used a Leopard 51 PC as the model yacht. The full report is available for download below.
Parallel Hybrid
"Two Motors On The Same Shaft"
A Parallel hybrid system places both an electric motor and diesel motor on the same propeller shaft. This system was popularized by Green Line and we believe it is the best way to electrify monohulls at this point in time. The typical configuration uses a smaller electric motor, usually two 20kW motors is all you need for 6-9 knots. Near docks and in 5 mile an hour zones passengers enjoy the silence and cleanliness of electric. For higher speed operation the diesel kicks in and users have the best of both worlds.
We recently started to offer this type hybrid method for re-fits and new builds for a couple reasons. First, the redundancy of having two motors on each shaft is great for Bluewater applications. Second, this configuration does not require a generator. The diesel motors are modified to output 10kW of power each and the electric machines on the shaft can also be used as generators. Third, for high speed operation over 1 hour, we recommend this configuration. Transfluid and Steyr are our suppliers of choice for this system. Fourth, because the electric motors are smaller, we can use a lower voltage which is both safer and easily converted to the voltage of the house load or powered by the solar panels.
What's best for your multihull? Speak with a Nova Luxe representative to learn more about your options!
