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The NRA Goes Electric

Electric Boat Motors

Kevin Bond, Operations Director of the National Rivers Authority, has seen his vision come to fruition this year. Lambourn, the well-kown Patrol Boat on the Middle Thames has had environmentally-friendly electric propulsion system added withoiut any loss of exisiting operational capabilities. In future, it will use its diesel engine only for powering its fire pumps and punping out, and providing high power for emergency use, fast stream condiitons and towing. For its normal eight-hour patrols it will run on silent, pollution-free electric motor.

Earlier this year, the Thames Electric Launch Co. were commissioned to install an electric drive to run in parallel with the existing Thornycroft 60hp diesel engine. This has been achieved by fitting a 5kW Lynch radial armature motor driving through clutches and a toothed rubber belt onto the existing drive shaft. Thus the propeller is driven either by the diesel or the electric motor. The clutch ensures that when the diesel is working, the electric motor is completely disconnected from the drive shaft. The Lynch motor is only 200mm diameter and 80mm long. It is designed to give a maximum 6kW but in this installation is set to provide 4.5kW at 36 volts and 130 amps. It is mounted just behind the diesel and runs at maximum rpm of 2300. This is reduced to the propeller shaft speed of 1200 rpm through the belt coupling.

The batteries are mounted in their own compartments forward and aft of the diesel. Two banks of six batteries are mounted forward and one bank is fitted aft, alongside the Lynch motor, the three sets being connected in parallel. The batteries are Chloride Trekker 3ER 175 ah monobloc tubular plate type. A 3” diameter ventilation pipe runs from each battery compartment through the coaming on either side of the launch. A Chloride Aqualert topping-up alarm is fitted to one of the port side batteries. Topping up will be through a Chloride Easifill semi-automatic system. The battery pack has been sized
to give six hours continuous running at about 5 mph. Including the time for passage through locks, when the motor will not be running, the launch can easily complete an eight hour shift on one charge. A large battery charger, the Chloride 210 30 volt 465 Ahr, is fitted in the driving cabin. The 240 volt mains supply is brought on board to a Marechal 16/32 socket and the land connection will be through the standard Marechal 32/50 four pin socket which is being fitted on all NRA charging points. The launch has been fitted with a corresponding earth monitoring system and in addition, an RCD is fitted on board.

The control system has been designed and fitted by Thames Electric Launch Co. using a Curtis MOSFET controller. This gives completely variable speed control both forward and astern. The system is powered up through a master switch and then an “ignition” switch that engages the main controller relay.

Instrumentation is simple, comprising a Curtis LED battery state meter, a 0-150 Ammeter and an Autohelm log/speedometer. The latter enables the helmsmen to best balance speed against power consumption, to give the maximum possible range.

With NRA Boatman Julian Kennard at the helm we set off on a simulated operational trip. Throw the master switch, turn the “ignition” key, cast off and we glided silently into the river above Caversham Lock. Opening the throttle the launch quickly gathered speed against the modest stream until at half throttle we reached operational cruising speed of 4.5pmh with the motor taking 60amps. After a short time at this setting, the throttle was moved to fully open, the speed then reaching 5.8mph with the motor taking about 130 amps. The motor and drive noise and vibration remained all the time at a low level. Moving the throttle from forward to full astern was made steadily with a slight pause in neutral to allow the electric motor clutch to change direction. The high inertia of the launch means that the change from forward to astern takes marginally longer with the electric motor than the much more powerful diesel but this is not regarded as a problem, and all drivers have so far expressed themselves perfectly happy with the performance.

A demonstration of the changeover from electric to diesel revealed one of the major advantages of this system. Moving forward at cruising speed, the electric throttle was closed and motor switched off. The diesel ignition key was turned to operate the starter. The engine immediately roared into life and being brought up to half throttle, the launch came back to cruising speed with hardly any overall drop in speed. But the noise and vibration of the diesel immediately impressed itself on us. It was a relief to switch back onto the electric motor.

The extra weight of the batteries adds about 1100 lbs. And causes the launch to sink about 1.25 inches into the water. This has an imperceptible effect on the wash but gives a slightly lower response time to the acceleration under electric power. Manoeuvrability is not affected, and the launch will still turn in virtually its own length, a necessity on the busy Thames.

There is no doubt that the use of electric power for normal patrol operation will greatly reduce the noise heard by the general public and will have a marked effect on the improved comfort level for the crew in the driving cabin, especially over a full working day. Other advantages, such as ease of operation, reduced maintenance and possibly lower operating cost have yet to be proved. One
operational requirement on Lambourn is that the diesel has to be warmed at the beginning of every patrol in order to ensure that its full performance is immediately available at any time during the patrol. However, this is a simple requirement, and overall the NRA are sufficiently impressed with this first
installation on the Lambourn that they have commissioned the first of their new 31ft launches to be fitted from new with a diesel-electric installation.

This boat is being built during the winter, and will appear alongside Lambourn next season. If the experience of the growing number of electric boat users is anything to go by, we can expect to see patrol boats on many waterways being converted to diesel-cum-electric. The system appears to give the best of both worlds for these multi-purpose vessels, but at the same time it would appear to have advantages for other private craft, particularly those with large diesel engines, who wish to travel silently on the rivers or canals. TELCOP are presently completing two more installations, one on a sea-going river launch, and the other on a canal boat.

 
         
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