The 40ft cruiser (below) has logged thousands of miles using the hybrid system above
automatically starts and stops the generator at low and high SoC.” There are additional settings for starting the generator, for example if a predetermined motor power is to be used for a predetermined time. The central module can be connected to the internet for remote diagnostics, updates, control and communication.
To date, OceanVolt has delivered 30 of these systems.
Meanwhile, Fischer Panda is now on its fourth generation of submersible (pod-type) electric machines together with the controllers and software that integrate these with Fischer Panda generators. Packages are designed for easy installation with the cables for the electric machine, the battery cables, the joystick and the helm display all plugging into a central control box, operating at a nominal 48 volts. Power levels are 10 kW and 20 kW. Given that boats rarely operate at wide open throttle for any length of time, and the fact that once you throttle back the load reduces dramatically, Fischer Panda recommends sizing generators at half the kW rating of the electric motor.
PARALLEL HYBRIDS
Recently, Fischer Panda has also begun adapting its electric machine technology to parallel hybrid applications. The electric machine is connected via a belt drive to the propeller shaft in a conventional installation, providing low speed maneuvering. The systems have been added to boats up to superyacht size. In calm conditions, the 20 kW electric motor is adequate to move these large boats at slow speeds in harbor.
This low-power, low-speed capability is a defining feature of parallel systems; no attempt is made to provide sustained electric propulsion at anywhere near cruising speeds. The goal is to have sufficient electric power and electric storage capacity (batteries) to handle low-power situations (notably maneuvering in harbor or motorsailing in a sailboat). The electric machine, when operating as a generator (i.e. driven by the propulsion engine) will be powerful enough to recharge the batteries rapidly, resulting in a house electrical system that will support the comforts of home without running a generator long hours.
By far the most successful implementation of the parallel approach is to be found in the Greenline series of powerboats, of which over 600 have now been built, with approximately 70 percent of these as parallel hybrids, in sizes from 33ft to 48ft, and a 65ft version on the way. The electric machine provides 15 kW of propulsive power and 10 kw of generating capability operating at a nominal 48 volts. The Greenlines include sizeable lithium-ion battery packs (soon to be provided by Torqeedo) enabling the use of overnight air conditioning without running a generator—an important consideration in the Mediterranean where many of these boats operate.
The Greenline approach is based on an integrated flywheel electric machine, initially built into a Volkswagen marine engine, but now integated into the Volvo-Penta D3. Note that a very similar approach has been adopted at one time or another by both Steyr and Nanni (two European marine diesel engine manufacturers). However, neither appear to be making much of an effort at the moment to improve or promote this technology. Part of the secret to success for the Greenlines has been to eliminate much of the complex software and control issues associated with fully-integrated parallel hybrids. Instead, the operator uses a switch to select between electric propulsion and diesel propulsion, at which point the electric motor becomes a generator.
So far as fully-integrated parallel hybrids for recreational boats are concerned, the only well-tested system of which I am aware comes from Hybrid Marine in the UK. This has been continuously developed and tested over a period of 12 years. It uses a 10 kW electric machine (or multiples of 10 kW) operating at a nominal 48 volts.
I was recently aboard Seaweed, a 40ft offshore cruising boat with a Hybrid Marine system, immediately after the owner returned from six years of cruising on both sides of the Atlantic. Seaweed had been sailed from the Hebrides to the Madeira Islands and from Nova Scotia to the West Indies. The owner was delighted with the hybrid performance, especially his ability to maneuver in a harbor under electric power, to regenerate from a freewheeling propeller when under sail (“I often used the electric kettle on passage when sailing at 6 knots or over and reckoned to recover the energy for my large mug of tea in about 40 minutes,” he says) and the ability to add a kilowatt or two of electric power to the propeller shaft when sailing in light winds, substantially boosting the boat’s speed with only a limited impact on the batteries.
Hybrid Marine has also installed systems in a number of recreational canal boats in the UK. The canals have a speed limit of 4 mph, but with occasional river sections that may have considerable currents. These boats have relatively large engines to handle the river sections, but are then effectively overpowered for most of the time they are underway. This is a chronically inefficient duty cycle for a conventional installation, but ideally suited to a parallel hybrid. Enough battery power can be provided to run all day in the canals under electric power. If it is not possible to plug in and recharge overnight, a relatively short run under conventional power will recharge the batteries, with the battery charging load adding sufficient load to the engine to create a reasonably efficient duty cycle even at low cruising speeds.
All of these companies are based in Holland, which seems to be the epicenter for large recreational vessel hybrid development. (Ferretti, in Italy, has also done one or two boats.) However, every one of these systems is individually engineered. Given the complexity of these large boats, I believe we are still some way from “generic” systems that can be dropped into more-or-less any boat with little customization.
What may change this situation is an emerging concept in the superyacht world known as the “hour of power.” The idea is to provide these boats with sufficient battery-powered electric propulsion to be able to operate at up to 10 knots for one hour to get in and out of harbors and anchorages, resulting in zero emissions. A battery pack large enough to do this will also support overnight air conditioning without running a generator. There may be a significant market for hybrid superyacht tenders that eliminate emissions when underway and when alongside the mother ship as well.
If the hour of power concept gains traction, we can expect to see considerable investment in hybrid systems for larger recreational boats. This may also be driven by legislation as more harbors look at the feasibility of implementing zero emissions rules. (Amsterdam, for example, has set a deadline of 2025.)
SOFTWARE AND BATTERY CHALLENGES
To be successful, any hybrid system, whether it is a serial or parallel hybrid, needs to have a control system that is, in effect, a whole-boat energy management system. On all but the simplest systems, this involves balancing and optimizing a mind-boggling number of possible permutations of, and interactions between, the components in the energy system: electric machines and their controllers, batteries, generators, other energy sources (shorepower, solar, wind, regeneration, maybe fuel cells), various voltage converters (DC-to-DC, DC-to-AC, AC-to-DC), and all the loads on the boat. At all times, the system must ensure a safe mode of operation, often