(This article appeared in "The Boater" magazine, June 1998)
Edward Hawthorne, Vice-President of the Electric Boat Association, outlines the history of electric propulsion on the Thames and describes present trends
During 1898 electric boat activity on the River Thames was growing apace. The Immisch Electric Launch Co. and the Thames Valley Launch Co. each had about sixty electric launches for hire, there were about the same number in private ownership and most of the large boat builders had experience in building, fitting out and hiring electric boats. Most electrics were launches ranging in size from 15 to 45ft. in length. The largest on the river, and for a long time in the world, was the 65ft. eighty-passenger 'Viscountess Bury', which plied on the Thames between 1888 and 1910 when she was converted to oil and taken up to Cambridge. A familiar sight on her trips between Cambridge and Denver she is now undergoing restoration and conversion back to electric propulsion.
The development of oil engines at the turn of the century and the effects of the First World War proved the death knell for electric propulsion - and steam. A few boatyards maintained electric canoes and some launches for hire, but by the mid 1930s even these had disappeared from the river and there was virtually no interest in electric boats on the Thames until about 1975.
The resurgence of interest was encouraged by the import of electric outboards developed in America as trolling motors for fishermen on the lakes, and by the practical activities of Rear Admiral Percy Gick and Lord St. Davids. The former, supported by the Midland Electricity Board, took an electric Trentcraft cruiser 600 miles up the Thames and around the canals and Lord St Davids moored a small narrow boat powered by prototype Lynch outboard motors at the bottom of his garden on the Regents Canal, whence he cruised over 4000 miles between 1981 and 1991. The two of them also founded the Electric Boat Association, the first of its kind in the world.
During the 1980s, Rupert Latham at Wroxham set out to develop the Frolic electric launch using GRP construction and an advanced electric propulsion system. To date, more than two hundred of them have been sold. The electric boat market in general was slow to materialize but has expanded rapidly during the last seven years. For example, in 1991, there were only two electric boats on the three-mile stretch between Cookham and Marlow; today there are more than thirty. Nine of the pre-1930s Thames launches and four canoes are still in use or undergoing restoration. Four of the launches have been converted to steam and one to petrol but the canoe, 'Gena', still has its original motor and controls. The traditional launch design with high length/beam ratio is still the most elegant type of electric boat and the skills of building in teak and mahogany are carried on by some yards on the Thames and in Norfolk. However, the growth market is in maintenance-free GRP hulls which not only cut costs but provide opportunities to design specially shaped low wash hulls. Interest is growing in the use of cruisers up to 35ft length. Electric narrowboats arrived in the early 1950s as hireboats but have not yet caught on.
In Austria electric ferries carry up to 200 passengers on trips across lakes where petrol or diesel engines are banned. It is interesting that the original electric boats on the Thames were designed as ferry boats for use in the Pool of London. Last year, Hammertons at Twickenham opened the first Thames electric ferry since the end of the last century. The main components of an inboard electric propulsion system (DIY kits are becoming available for those who wish to do their own installation or conversion) are:
Batteries: The batteries of 1896 were lead-acid 2-volt single cells with removable plates and with a typical capacity of 30 watthours/litre. Today's batteries store 100 watthours/litre in a sealed 6 volt monobloc containing 3 cells. Liquid electrolyte is the most common in use but gel electrolyte cuts out the need to top up, although at some slight loss in performance. Batteries can be the most costly item in the electrical system and users are therefore acutely interested in the life which can be expected. Most industrial battery applications are rated at a life of 1500 cycles equivalent to 5 years of normal industrial usage, but the lower usage of most boats means that, if properly treated, modern batteries should last at least seven years and lives of 10 to 15 years have been quoted. The golden rule is never to overcharge and try not to discharge more than 80 per cent of capacity.
Motors: Until recently, the motors used in boats were standard industrial DC series types with axial armatures and run at speeds at which they could be directly coupled to the propeller. A typical 1.4kw motor would have dimensions of 11in x 10in diameter, a weight of l00lb and an efficiency of about 80 per cent. Motor size can be reduced by increasing motor rpm and fitting a gearbox as in the Brimbelow E drive system. However, during the last ten years the radial armature motor reinvented by Cedric Lynch has been developed and is increasingly being used. Not only is such a motor much smaller (eg a 5" x 8" diameter motor will provide 1 to 8.5kw continuously and weigh 241b) but the efficiency is 90 per cent, thereby adding 11 percent to the boat's range. One snag is that these motors run at 2000 to 4000rpm and have to be geared down to the propeller. One manufacturer is now taking advantage of the small size to build a Lynch motor in the head of an outboard and therefore out of the water. The brushes of electric motors inevitably make some noise and this is usually more or less eliminated by sound-proofing. But it is sometimes not realised that using anti-vibration mountings can materially reduce the noise transmitted through the hull. Gearing between motor and propeller can also produce a surprising amount of noise and this can generally be reduced by using belt drives. Of course, electric boat users, like steam boat enthusiasts, are so used to very low noise levels that any increase becomes irritating!
Controllers: The Curtis pulse modulated controller based on solid state technology is fitted in many electric boats and provides infinitely variable forward and astern speeds. This probably enhances the reliability of batteries and motors by providing smooth changes in speed although there are a few percentage points of loss. The traditional switch system, usually giving up to four forward and two astern speeds is now very reliable, cheaper and quite satisfactory for the smaller boats. There are no losses in the switch but corrosion and arcing can occur and may reduce life.
Chargers: For dinghies and small boats fitted with only one or two batteries it is usual practice to take the batteries out and charge them on the land. If enough time is available, trickle charging can be used but it is always better to use an automatic charger in order to avoid any risk of overcharging. Traditional chargers are transformer types, but the new high frequency switching technology can reduce charger size and weights by up to 80%. Most boats larger than dinghies carry their chargers onboard with a normal 13 or 15 amp cable carrying the mains supply to the boat. Many pubs and the like are prepared to allow boat-owners to plug in - "a pint and a charge, please", as Lord St. Davids used to say to the landlord. Virtually any powered leisure boat can be electric but it is important to match the electrical system to the boat's operational requirements, the essence being to reconcile speed and range. Batteries are limited in capacity (i.e. ampere-hours); speed is a function of power which at a given voltage is itself a function of current flow (i.e. amps). Therefore the higher the amps the higher the speed but the lower the running time. A 21ft open launch may require a current of 50 Amps at 48 volts to reach a speed of 6.5mph with a range of 36 miles, whereas at 5 amps and a cruising speed of 3 mph a corresponding distance of about 170 miles could be achieved. For example, the EBA 24-hour Endurance Record on a single charge for a battery powered 31 ft saloon launch is 116 miles at an average speed of 4.8mph. Contrary to popular belief, electric boats can go fast. Lady Arran established the world speed record of 50.8 mph in 1989 only to have the Americans capture it at a speed of 70.6 mph in 1996.
The Electric Boat Association publishes information sheets and a quarterly news magazine. Contact Barbara Penniall (Tel: 01491 681449. Fax: 0149 1 681945. e-mail: firstname.lastname@example.org). For the history of electric boats until 1914, see "Electric Boats on the Thames", Edward Hawthorne, Alan Sutton Publishing. For boatbuilding see "Electric Boats", Douglas Little, International Marine USA and distributed in the UK by Airlife Publishing Ltd.