Is marine electric propulsion settling on a 48 volt ‘standard’?

Because there is a balanced relationship between the load (amps), the energy that load requires (Watts) and the voltage, higher voltages mean less amps to provide a given amount of energy. (Watts = Volts x Amps). Wire sizes are dictated by the amps the wire carries. This means a 12-volt system drawing, say, 3000 Watts, enough to propel a small racing dayboat in calm water, would carry 250 amps (3000 divided by 12). But a 48 volt system producing the same 3kW would only carry 62.5 amps (3000/ 48). The wire gauge required by 62.5 amps is significantly smaller than that required by 250 amps, and the voltage drop effects on long wire runs, even more of an issue on longer boats, will be less pronounced. Heavier gauge wiring is bulkier to run through conduits, heavier and more expensive than lighter gauges. The more electronics or equipment boats have, the more wiring they require, and anything that enables lighter gauge wiring is of great benefit on any boat.

HUGE BENEFITS

The advantages are not limited to wiring runs though, in the case of propelling boats electrically, huge benefits within the motor itself are available when transitioning to higher voltages. Inside a brushless dc (BLDC) motor, as used on most VETUS marine propulsion systems, motion relies on the interaction of the rotor magnetic field and a rotating magnetic field generated by time-controlled currents in the copper stator windings. As the motor operating voltage increases for a given input power, it reduces the input root mean square current (RMS) and, therefore, the stator winding copper losses.

This presents the possible benefit of reducing the copper winding wire diameter inside the motor, introducing weight, volume, and cost savings. Copper is both expensive and heavy.

The volume saving becomes critical where electrically propelled boats house their motor under the hull floor with direct drive to the propeller. The motor diameter effectively dictates the size of the propeller hub, and the smaller we can make a propeller hub the more hydrodynamically efficient it can be.

As boats become bigger, equipment such as bow thrusters also become bigger, so bringing factors such as voltage drop and wire gauge into sharper relief.

HIGHER VOLTAGE?

One possible question could be: ‘If higher voltages are so advantageous, why don’t boats just adopt the 400 volt or even the latest 800-volt systems used on electric cars?’ The issue with this is safety in the marine environment. Little legislation yet exists, setting ‘standard’ safe voltages for marine systems, but water is relatively conductive, so in the marine environment it is easier to envisage an electric shock situation happening than with a road vehicle. With this danger in mind, legislators are looking at setting marine standards, with the EU seeming to favour a 50 volt limit.

Higher voltages will be possible, but it is likely they will come with significant legislative burden, perhaps even individual inspection and certification, as running higher voltages in water requires considerable additional safety considerations. Other jurisdictions have been looking at 80 volts but it is looking like the critical mass of opinion is settling on a 50 volt limit, which in a practical sense means a 48 volt marine electronics standard.

Without delving too deeply into the history books, it’s worth asking why we have ended up with so many boats with 12 volt systems if 12 volts means heavier, more expensive, thicker gauge wiring and less motor efficiency than higher voltage systems. Early boat systems were 12 volts as 12 volts was the de facto automotive standard. 12 volts was fine for cars; few wiring runs will exceed 4m in a car so issues such as voltage drop over long runs was not much of an issue. But as boats got bigger, 12 volts as a standard started to struggle and with bigger boats using truck-derived engines with their 24 volt systems, we moved to 24 volts and now, increasingly on to 48 volts. Hydraulics also gained popularity to mitigate the problems of voltage drop, but hydraulic fluid is heavy in long pipe runs, needs changing periodically and can cause expensive damage in the event of a leak.

It’s not practical to switch all boat systems to 48 volts yet though. Certain accessories such as bilge pumps are not yet widely available in 48 volts. So most modern yachts being built will have a mix of 24 and 12 volts for many systems, often with 48 volts available too for electric propulsion and thrusters.

PLUG AND PLAY

VETUS, as a creator of boat systems is getting behind 48 volts as a future ‘standard’ voltage for electric marine propulsion. Thinking back to what we said about higher voltages attracting additional legislative burden, VETUS systems are largely plug and play. To meet VETUS’ decarbonisation aims of marine electrification engaging as many boaters as quickly as possible, plug and play systems are necessary. As VETUS R&D Director Arthur Roeling puts it: “A boat owner repowering a diesel-driven boat needs to find it not much harder to opt for electrification as they would replacing with yet another diesel. Products such as our E-Line and E-POD drives, both available in 48 volt configuration, carry their controllers in the casing and are direct drive, thus taking away much of the guesswork from a marine electrification project. The compact E-LINE motor range is designed to fit existing propulsion foundations and propeller shaft installations. The supplied Swap & Go mounting brackets, with motor mounts specifically developed for electric propulsion motors, can easily be adjusted in height and set to angle the shaft to 0° or 8°. This makes repowering and connecting to an existing propeller shaft a simple task. Somebody building or refitting yacht with electrical propulsion wants the peace of mind of a safe voltage and does not need the burden of bespoke equipment and extensive paperwork that allows a less safe voltage to be run.”

Up at the foredeck, VETUS and its subsidiaries have led the world for many years on bow thrusters and windlasses, so its choice to make much of the range 48 volts compatible is a move that the rest of the industry has noticed. VETUS BOW PRO 48VDC series and BOW PRO Boosted series (180 kgf – 400 kgf thruster models, are all 48 volt compatible, as are the Maxwell Power and Sailboat range of windlasses from RC8 through RC12 models and matching capstans.

As the industry transitions to higher voltages, it is critical not to leave existing boats behind. So, to accommodate this, all BOW PRO Boosted (BOWB) thrusters include an exclusive built in, patented DC-to-DC smart charger function that allows 24 VDC thruster battery banks to be charged by a 12 VDC power supply and in the case of 48 VDC BOWB, to be charged from an existing 24 VDC power supply. BOWB thrusters do this through a third charge connection on the thruster. This charge connection is constantly monitored and is only activated once the voltage level of the charging source reaches a suitable level. This feature prevents the charging source from being depleted; an important consideration if the circuit includes the engine starting bank. They then boost that input to a higher voltage and regulate it in a smart way to charge the thruster supply bank. In practice, this means skippers can connect the 24 VDC BOWB with a 12 VDC power supply or 48 VDC BOWB with a 24VDC power supply to charge its battery bank. The built in smart three stage charging process ensures that the thruster batteries are kept at their optimum level. When the thruster is not in use, the built-in charger automatically recharges the battery, doubling its value as both a thruster and charger. VETUS also offers the necessary battery banks to power up these products.

All VETUS 48V products can connect with the VETUS V-CAN CAN bus network. The development of this proprietary V-CAN protocol enables VETUS to maintain the implemented safety factors which are built into its products.

The company has also designed a range of products which will communicate between this proprietary V-CAN system and J1939 or NMEA2000 networks, again to further drive home the ‘plug and play’ advantages of its systems.

In conclusion, VETUS Marketing Director Sander Gesink says: “There has been a lot of to and for about higher voltages for boats, especially in the last decade as electric propulsion has come to the fore. As with all areas of debate, the market ultimately decides and more and more items of 48 volt marine equipment are becoming available by the day, indicating that the movement towards a 48 volt ‘standard’ has now reached a critical mass. At VETUS we are pleased to see and be part of this. The adoption of any greater level of standardisation in the market means that manufacturers such as VETUS can have the confidence to develop more and better products, more rapidly to drive the decarbonisation process, which, at the end of the day, is what we are all about.”