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Each season, The Green Blue will be posting a new topic. If you have a topic you would like to see covered, or can share advice with others, get in touch.
This season’s article comes from David Parker of Warsash, Hampshire and is investigating the advantages of electric outboards.
The start of another sailing season is upon us and as you prepare your boat for another summer out on the water you may be considering investing in a new outboard engine. Electric outboards have made huge improvements in performance since they were first introduced. They are environmentally friendly, cheap to run and very quiet.
If you have never used an electric outboard motor before, the first thing you will notice is how quiet they are. They produce little or no vibration and don’t produce any emissions either which makes them ideal for environmentally friendly boating. They are cleaner for our waters and the boat owner too, because being powered by batteries there is no messing about with fuel or oil. They also require little or no maintenance; the most a motor should require is a wash down after use.
Typically electric outboards are mounted on the transom. The electric motor itself is mounted at the bottom of the motor shaft in an integral housing providing direct drive to the propeller. Unlike a conventional outboard, the shaft has no revolving parts and because the motor sits directly behind the prop in the water, no power is lost through drive shafts or gearboxes. Internal combustion engines are only about 26% efficient whereas electric outboards are 70% plus efficient.
Electric outboard motors first gained popularity is the United States where they are widely used for trolling when fishing. However their silence is not just appreciated by fishermen; if you enjoy watching wildlife they offer the least intrusive way to get closer to nature when afloat. Because trolling motors were not initially designed as the primary propulsion system for 
any boat they lack the thrust of a conventional outboard so are usually only suitable for inland or sheltered waters. Also cruising distance needs to be carefully calculated unless you have some means of topping up the battery on board such as a solar panel or wind charger.
When it comes to choosing an electric motor the biggest difference from petrol outboards regarding specifications is that the electric motors are not measured in horsepower but in thrust. Thrust can range from anything from a 28lb (12.7kg) motor with a 12 volt battery to drive a dinghy, to over 202lbs (92kg) for a boat over 25 feet which requires 36 volts to power it.
Electric outboard motors are easy to install and use, are very quiet and produce no emissions
Two of the most popular makes of electric motors distributed in the UK are Minn Kota and MotorGuide. Yamaha also offer a range of electric drive units and these are manufactured by the OMC Marine and Mercury group which also manufactures the MotorGuide range. Motors such as Electron and Combi are also made for hire fleets.
Different brands vary in design characteristics and build quality, so if possible try before you buy. The Minn Kota range distributed by Johnson Outdoors Watercraft includes both a freshwater and salt water series. Minn Kota also produces a wide range of accessories such as units with integral sonar transducers and motors which can even be steered by remote control. They also have an engine mount version so you have the option of switching between petrol and electric power.
More recently a whole new concept in electric outboard motors has come on to the market in the shape of Torqeedo engines from Germany. They are more expensive but have been designed to be used as the primary propulsion units using specially developed ‘torque’ motors. The Torqeedo Travel weighs 12 kg (26.5lbs) and folds into a waterproof rucksack for storage and transportation. Designed for the dinghy and daysailer market it has its own integral battery. The powerful torque motors perform well but are noisier than the existing trolling designs. The Torqeedo Cruise is a 24 volt model weighing 16kg (35lbs) and is powered by an external battery. It has been developed for larger craft such as sailboats.
For the majority of electric outboards, the traditional 12 volt deep cycle wet lead acid marine battery still remains the most economical and practical power source. Sometimes it’s called a leisure or traction battery and also comes in maintenance free sealed or gel designs. Deep cycle batteries are required because they are more tolerant of constantly being used, run down and then recharged. The battery should have a rating of at least 85 amp hours. Bear in mind the higher the current draw the quicker the battery becomes flat, so ease up on the throttle to make your batteries last longer afloat.
Multiple batteries can be connected in parallel or in series depending on what’s required. If you connect the negative to negative terminal and positive to positive terminals of any two batteries they are described as in parallel i.e. if they are 12 volts each, the output would still be 12 volts but you have doubled the amp hour rating (how long they’ll last). When you connect batteries in series you connect one negative terminal to the other battery’s positive terminal and then use the remaining two free terminals to deliver the power. This is how you turn a pair of lighter, more manageable six volt batteries into one with a 12 volt output – in simple terms you’ve doubled the series of cells, hence the term in series connection.
Whether you go for a traditional or maintenance free type battery depends on how you are going to use it. With a maintenance free battery it is not advisable to discharge greater that 60/70% of the capacity of the cell, but with a traditional flooded battery you can easily go to 80% depth of discharge. However with a wet battery when it’s left and not fully charged it 
gets sulphated and goes flat. Maintenance free batteries don’t degrade as much when not used and maintain their charge for long periods. Wet batteries which aren’t sealed will also requiring topping up with fluid over time. Never fill a cell right to the top because the liquid will bubble out and you’ll get battery acid all over the boat and only used de-mineralised, de-ionised or distilled water for topping up. Always dispose of old batteries by taking them to an appropriate collection point.
The charger you purchase to keep your battery healthy is also important. It pays to invest in a decent ‘switch mode’ chargers; these are often called ‘smart’ or ‘intelligent’ chargers and they constantly monitor and regulate the charge being delivered to the battery. The built in micro-processor controlling the charging levels knows when the battery’s had enough and therefore prevents battery damage due to overcharging. When charging any battery remember that the gases given off are explosive so don’t do your charging near any naked flames, sparks or in an encased battery box with no ventilation.
Torqeedo motors have recently been developed and the
Travel version is available with integral batteries
www.minnkotamotors.com
www.barrus.co.uk
www.mailspeedmarine.com
www.thameselectric.com
www.cmpbatteries.co.uk
www.electric-boat-association.org.uk
www.barden-uk.com
» Wind and solar power - a cruisers perspective
»
Fitting a holding tank to a Nauticat 33
» Don't spill the fuel when you fill up
» Winterisation and service of outboard engines
» Laying up your inboard engine
The RYA publishes a wide range of handbooks covering engine maintenance issues covering both inboards and outboards. There are also DVD and video guides, and the RYA Diesel Engine Course provides and excellent entry level qualification for those who need to know more about their engine.
For publications visit: http://www.rya.org.uk/Shop/
