Electric boat

Moritz von Jacobi, inventor of an early electric boat

An early electric boat was developed by the German inventor Moritz von Jacobi in 1839 in St Petersburg, Russia. It was a 24-foot (7.3 m) boat which carried 14 passengers at 3 miles per hour (4.8 km/h). It was successfully demonstrated to Emperor Nicholas I of Russia on the Neva River.

Outboard motorboat of Gustave Trouvé in 1881

It took more than 30 years of battery and motor development before the electric boat became a practical proposition. This method of propulsion enjoyed something of a golden age from about 1880 to 1920, when gasoline-powered outboard motors became the dominant method. Gustave Trouvé, a French electrical engineer, patented a small electric motor in 1880. He initially suggested that the motor could power a set of paddle wheels to propel boats on the water, and later argued for the use of a propeller.

Electric motor designed by Immisch & Co., who established the first fleet of electric launches in London

An Austrian émigré to Britain, Anthony Reckenzaun, was instrumental in the development of the first practical electric boats. While working as an engineer for the Electrical Power Storage Company, he undertook much original and pioneering work on various forms of electric traction. In 1882 he designed the first significant electric launch driven by storage batteries, and named the boat Electricity.[3] The boat had a steel hull and was over seven metres long. The batteries and electric equipment were hidden from view beneath the seating area, increasing the space available for the accommodation of passengers. The boats were used for leisure excursions up and down the River Thames and provided a very smooth, clean and quiet trip. The boat could run for six hours and operate at an average speed of 8 miles per hour.[4]

Moritz Immisch established his company in 1882 in partnership with William Keppel, 7th Earl of Albemarle, specializing in the application of electric motors to transportation. The company employed Magnus Volk as a manager in the development of their electric launch department. After 12 months of experimental work starting in 1888 with a randan skiff, the firm commissioned the construction of hulls which they equipped with electrical apparatus. The world's first fleet of electric launches for hire, with a chain of electrical charging stations, was established along the River Thames in the 1880s. An 1893 pleasure map of the Thames shows eight "charging stations for electric launches" between Kew (Strand-on-the-Green) and Reading (Caversham).[1] The company built its headquarters on the island called Platt's Eyot.

From 1889 until just before the First World War the boating season and regattas saw the silent electric boats plying their way up and downstream.[5]

Early electric launch on the River Thames, built by William Sargeant

The company's electric launches were widely used by the rich as a conveyance along the river. Grand ships were constructed of teak or mahogany and furnished luxuriously, with stained glass windows, silk curtains and velvet cushions. William Sargeant was commissioned by Immisch's company to build the Mary Gordon in 1898 for Leeds City Council for use on the Roundhay Park Lake – the boat still survives and is currently being restored.[6] This 70-foot long luxury pleasure craft could carry up to 75 passengers in comfort. Launches were exported elsewhere – they were used in the Lake District and all over the world.

In the 1893 Chicago World Fair 55 launches developed from Anthony Reckenzaun's work carried more than a million passengers.[7][8] Electric boats had an early period of popularity between around 1890 and 1920, before the emergence of the internal combustion engine drove them out of most applications.

Most of the electric boats of this era were small passenger boats on non-tidal waters at a time when the only power alternative was steam.

With the advent of the gasoline-powered outboard motor, the use of electric power on boats declined from the 1920s. However, in a few situations, the use of electric boats has persisted from the early 20th century to the present day. One of these is on the Königssee lake, near Berchtesgaden in south-eastern Germany. Here the lake is considered so environmentally sensitive that steam and motor boats have been prohibited since 1909. Instead the Bayerische Seenschifffahrt company and its predecessors have operated a fleet of electric launches to provide a public passenger service on the lake.[9][10][11]

The first electrically powered submarines were built in the 1890s, such as the Spanish Peral submarine, launched in 1888.[12] Since then, electric power has been used almost exclusively for the powering of submarines underwater (traditionally by batteries), although diesel was used for directly powering the propeller while on the surface until the development of diesel–electric transmission by the US Navy in 1928, in which the propeller was always powered by an electric motor, energy coming from batteries while submerged or diesel generator while surfaced.

The use of combined fuel and electric propulsion (combined diesel–electric or gas, or CODLOG) has gradually been extended over the years to the extent that some modern liners such as the Queen Mary 2 use only electric motors for the actual propulsion, powered by diesel and gas turbine engines. The advantages include being able to run the fuel engines at an optimal speed at all times and being able to mount the electric motor in a pod which may be rotated by 360° for increased manoeuvrability. Note that this is not actually an electric boat, but rather a variant of diesel–electric or turbine-electric propulsion, similar to the diesel or electric propulsion used on submarines since WWI.

An electric passenger launch on Lake Königssee in Germany

The use of electricity alone to power boats stagnated apart from their outboard use as trolling motors until the Duffy Electric Boat Company of California started mass-producing small electric craft in 1968. It was not until 1982 that the Electric Boat Association was formed and solar powered boats started to emerge.[13] To reduce friction and increase range, some boats use hydrofoils.[14]

Electric energy has to be obtained for the battery bank from some source like the sun.

• A mains charger allows the boat to be charged from shore-side power when available. Shore-based power stations are subject to much stricter environmental controls than the average marine diesel or outboard motor. By purchasing green electricity it is possible to operate electric boats using sustainable or renewable energy. For large vessels, an onshore battery may be necessary to provide more short-term power than the grid can supply.

2.5 MW Automatic coupling robot charger for the Herjólfur Ferry in Iceland.

• Solar panels can be built into the boat in reasonable areas in the deck, cabin roof or as awnings. Some solar panels, or photovoltaic arrays, can be flexible enough to fit to slightly curved surfaces and can be ordered in unusual shapes and sizes. Nonetheless, the heavier, rigid mono-crystalline types are more efficient in terms of energy output per square meter. The efficiency of solar panels rapidly decreases when they are not pointed directly at the sun, so some way of tilting the arrays while under way is very advantageous.
• Towed generators are common on long-distance cruising yachts and can generate a lot of power when travelling under sail. If an electric boat has sails as well, and will be used in deep water (deeper than about 15 m or 50 ft), then a towed generator can help build up battery charge while sailing (there is no point in trailing such a generator while under electric propulsion as the extra drag from the generator would waste more electricity than it generates). Some electric power systems use the free-wheeling drive propeller to generate charge through the drive motor when sailing, but this system, including the design of the propeller and any gearing, cannot be optimised for both functions. It may be better locked off or feathered while the towed generator's more efficient turbine gathers energy.
• Wind turbines are common on cruising yachts and can be very well suited to electric boats. There are safety considerations regarding the spinning blades, especially in a strong wind. It is important that the boat is big enough that the turbine can be mounted out of the way of all passengers and crew under all circumstances, including when alongside a dock, a bank or a pier. It is also important that the boat is big enough and stable enough that the top hamper created by the turbine on its pole or mast does not compromise its stability in a strong wind or gale. Large enough wind generators could produce a completely wind-powered electric boat. No such boats are yet known although a few mechanical wind turbine powered boats exist.
• In hybrid electric boats, if a boat has an internal combustion engine anyway, then its alternator will provide significant charge when it is running. Two schemes are in use: the combustion engine and the electric motor are both coupled to the drive (parallel hybrid), or the combustion engine drives a generator only for charging the storage batteries (series hybrid).

In all cases, a charge regulator is needed. This ensures that the batteries are charged at their maximum safe rate when power is available, without overheating or internal damage, and that they are not overcharged when nearing full charge.

An alternative to charging is changing batteries while in port. It offers the benefit of removing the need to wait for the recharging to complete before sailing. This approach has the potential to allow ships and ferries with tight schedules to be electrified as charging can be done in port with no time limitations.[15]

Example of a modern production electric boat

SB Collinda, the first solar powered boat to cross the English Channel, seen here in Bristol Harbour

There have been significant technical advances in battery technology in recent years, and more are to be expected in the future.

• Lead–acid batteries were still the most viable option until the advent of larger, lithium-ion batteries mass-produced for electric cars from approximately 2012 onwards. Deep-cycle, 'traction' batteries are the obvious choice. They are heavy and bulky, but not much more so than the diesel engine, tanks and fittings that they may replace. They need to be securely mounted, low down and centrally situated in the boat. It is essential that they cannot move around under any circumstances. Care must be taken that there is no risk of the strong acid being spilled in the event of a capsize as this could be very dangerous. Venting of explosive hydrogen and oxygen gases is also necessary. Typical lead-acid batteries must be kept topped-up with distilled water.
• Valve-regulated lead-acid batteries (VRLA), usually known as sealed lead-acid, gel, or AGM batteries, minimize the risk of spillage, and gases are only vented when the batteries are overcharged. These batteries require minimal maintenance, as they cannot and usually do not need to be refilled with water.
• Nickel metal hydride, lithium-ion and other battery types are becoming available, but are still expensive. These are the kind of batteries currently common in rechargeable hand tools like drills and screwdrivers, but they are relatively new to this environment. They require different charge controllers to those that suit lead-acid types.
• Lithium-ion in this case usually means lithium iron phosphate batteries, which although are heavier than other lithium-ion, is safer for marine application. They are expensive but in applications which need reliability and ruggedness like ferries which run most of the day (10–12 hours/day) this is the best option. It has a much longer life – 5 to 7 years life-cycle.
• Fuel cells or flow batteries may provide significant advantages in years to come. Today (2017) however they are still expensive and require specialist equipment and knowledge.

The size of the battery bank determines the range of the boat under electric power. The speed at which the boat is motored also affects range – a lower speed can make a big difference to the energy required to move a hull. Other factors that affect range include sea-state, currents, windage and any charge that can be reclaimed while under way, for example by solar panels in full sun. A wind turbine in a good wind will help, and motor-sailing in any wind could do so even more.

To make the boat usable and manoeuvrable, a simple-to-operate forward/stop/backwards speed controller is needed. This must be efficient—i.e. it must not get hot and waste energy at any speed—and it must be able to stand the full current that could conceivably flow under any full-load condition. One of the most common types of speed controllers uses pulse-width modulation (PWM). PWM controllers send high frequency pulses of power to the motor(s). As more power is needed the pulses become longer in duration.

A wide variety of electric motor technologies are in use. Traditional field-wound DC motors were and still are used. Today many boats use lightweight permanent magnet DC motors. The advantage of both types is that while the speed can be controlled electronically, this is not a requirement. Some boats use AC motors or permanent magnet brushless motors. The advantages of these are the lack of commutators which can wear out or fail and the often lower currents allowing thinner cables; the disadvantages are the total reliance on the required electronic controllers and the usually high voltages which require a high standard of insulation.

An example of an electric retrofit. Two 9 kW LMC motors powered by 16 Interstate deep-cycle 6-volt batteries.

Traditional boats use an inboard motor powering a propeller through a propeller shaft complete with bearings and seals. Often a gear reduction is incorporated in order to be able to use a larger more efficient propeller. This can be a traditional gear box, coaxial planetary gears or a transmission with belts or chains. Because of the inevitable loss associated with gearing, many drives eliminate it by using slow high-torque motors. The electric motor can be encapsulated into a pod with the propeller and fixed outside the hull (saildrive) or on an outboard fixture (outboard motor).

The electric ferry Steffi on the Straussee, 30 km east of Berlin

Trolley boats are a special category of electric boats are the vessels receiving their electrical power by wire. This may involve overhead wires, where one or two wires are fixed over the water and the boat can make contact with them to draw electric current, or a waterproof tether cable may be used to connect the boat to shore. In case of a single overhead wire the electrical circuit has to be closed by the water itself, giving rise to a larger resistance and corrosion of the electrodes. In case of two wires no electric current has to be sent through the water, but the twin wires, which cause a short-circuit whenever they come into contact with each other, complicate the construction.

Naturally the boat has to stay close to the wire, or its tether point, and therefore it is limited in its manoeuvrability. For ferries and on narrow canals this is no problem. The Straussee Ferry in Strausberg, Germany is an example. It crosses a lake along a 370 m trajectory and is powered by 170 V from a single overhead wire. The Kastellet ferry crosses a 200 metres (660 ft) wide shipping channel in Sweden, using a submergible tethered supply cable which is lowered to the sea-bed when the ferry is docked at the opposite terminal to its tethering point.

In the Mauvages tunnel on the Marne-Rhine Canal a bipolar overhead line provides 600 V DC to an electrical tug, pulling itself and several ships through the 4877 m tunnel along a submerged chain. This prevents the buildup of diesel exhaust fumes in the tunnel. Another example was the experimental electrical tug Teltow on the Kleinmachnower See, 17 km south-west of Berlin. It was used from 1903 until 1910 and had current collection poles based on those used by trolley buses.

The British Classic Boat magazine carried a pro and con article entitled Electric debate in May 2010,[41] when lead-acid batteries dominated the battery market, and fossil fuels dominated the UK electricity system. Jamie Campbell argued against electric boating on four main counts, which were rebuffed by Kevin Desmond and Ian Rutter of the Electric Boat Association. Jamie Campbell asserted that electric propulsion can no more be justified afloat than a Seagull outboard motor, proposing wooden sailing boats and rowing dinghies as "by far the most environmentally sensitive and renewable options for recreational boating".

Campbell asserts that the lack of pollution from an electric boat "reeks of nimbyism" as "the discharge is all in someone else's back yard" and that the provision of re-charging points may involve digging up miles of habitat. Desmond responds that while there is no doubt that rechargeable batteries derive their energy from power stations (when not charged on board by solar and wind generation), noisier internal-combustion-engined boats obtain their fuel from even further away and that, once installed a power cable is less environmentally disruptive than a petrol station. Rutter notes that electric boats tend to recharge overnight, using 'base load'.

While there are losses in the charge/discharge cycle and in the conversion of electricity to motive power, Rutter points out that most electric boats need only about 1.5 kW or 2 hp to cruise at 5 mph (8 km/h), a common maximum river speed and that a 30 hp (22 kW) petrol or diesel engine producing only 2 hp (1.5 kW) is considerably more inefficient. While Campbell refers to heavy batteries requiring a "load-bearing hull" and "cranky, even unseaworthy vessels", Desmond points out that electric boaters tend to prefer efficient, low-wash hull forms that are more friendly to river banks.

Campbell discusses the pollution that "traditional" batteries put into the water when a boat sinks, but Desmond says that electric boats are no more liable to sinking than other types and lists the leakage of fuel, engine oil and coolant additives as inevitable when an internal-combustion-engined boat sinks. Rutter points to the "very nasty cocktail of pollutants" that come out of a diesel wet exhaust in normal use.

Campbell mentions "all manner of noxious chemicals ... involved in battery manufacture", but Rutter describes them as being "lead and sulphuric acid with a few extra trace metals in a modest plastic box" with a potential lifetime of 10–12 years. Desmond says that the US has a 98% recycling rate for lead acid batteries and that the battery and lead-smelting industries observe some of the tightest pollution control standards in the world.

The article mentions 25% and 30% discounts being offered to electric boaters by the UK Environment Agency and the Broads Authority and that battery powered vehicles have 3⁄5 the carbon footprint of their petrol equivalents. It is claimed that a typical recharge after a day's cruising costs £1.50, without the use of solar or wind power.[41]