Electric Boat - Types

Types

There are as many types of electric boat as there are boats with any other method of propulsion, but some types are significant for various reasons.

• Historical and restored electric boats exist and are often important projects for those involved. See the Mary Gordon Electric Boat for example.

• Canal, river and lake boats. Electric boats, with their limited range and performance, have tended to be used mostly on inland waterways, where their complete lack of local pollution is a significant advantage. Electric drives are also available as auxiliary propulsion for sailing yachts on inland waters.

• Electric outboards and trolling motors have been available for some years at prices from about $100 (US) up to several thousand. These require external batteries in the bottom of the boat, but are otherwise practical one-piece items. Most available electric outboards are not as efficient as custom drives, but are optimised for their intended use, e.g. for inland waterway fishermen. They are quiet and they do not pollute the water or the air, so they do not scare away or harm fish, birds and other wildlife. Combined with modern waterproof battery packs, electric outboards are also ideal for yacht tenders and other inshore pleasure boats.

• Cruising yachts usually have an auxiliary engine, and there are two main uses for it: One is to power ahead or motor-sail at sea when the wind is light or from the wrong direction. The other is to provide the last 10 minutes or so of propulsion when the boat is in port and needs to be manoeuvred into a tight berth in a crowded and confined marina or harbour. Electric propulsion is not suitable for prolonged cruising at full power although the power required to motor slowly in light airs and calm seas is small. Regarding the second case, electric drives are ideally suited as they can be finely controlled and can provide substantial power for short periods of time.

• Diesel-electric hybrid. There is a third potential use for a diesel auxiliary and that is to charge the batteries, when they suddenly start to wane far from shore in the middle of the night, or at anchor after some days of living aboard. In this case, where this kind of use is to be expected, perhaps on a larger cruising yacht, then a combined diesel-electric solution may be designed from the start. The diesel engine is installed with the prime purpose of charging the battery banks, and the electric motor with that of propulsion. There is some reduction in efficiency if motoring for long distances as the diesel's power is converted first to electricity and then to motion, but there is a balancing saving every time the wind-, sail- and solar-charged batteries are used for manoeuvring and for short journeys without starting the diesel. There is the flexibility of being able to start the diesel as a pure generator whenever required. The main losses are in weight and installation cost, but on the bigger cruising boats that may sit at anchor running large diesels for hours every day, these are not too big an issue, compared to the savings that can be made at other times.

• Solar powered. A boat propelled by direct solar energy is a marine solar vehicle. The available sunlight is almost always converted to electricity by solar cells, temporarily stored in accumulator batteries, and used to drive a propeller through an electric motor. Power levels are usually on the order of a few hundred watts to a few kilowatts. Solar powered boats started to become known around 1985 and in 1995 the first commercial solar passenger boats appeared. Solar powered boats have been used successfully at sea. The first crossing of the Atlantic Ocean was achieved in the winter of 2006/2007 by the solar catamaran Sun21.