How to choose an electric propulsion system for your boat ?

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how to choose an electric propulsion system

The popularity of electric engines

Heat engines are more and more criticized and there are many reasons for this bad popularity. Of course, the first argument is the pollution, as well as the noise. Those arguments justify, for plenty of administration, the restriction of heat engines on their lake, river and waterway. By the way, the number of waterways accessible by heat engine is decreasing and people owning those polluting motors are pushed to set up electric systems on their boat.

In this way, more and more users go for electric motor on their craft, particularly popular in France, in renting boat business, especially for economic and practical reasons.

An electric engine can be used as auxiliary motor for fishing for example. It enable soft arrival in spots and better orientation control of the boat.

Electrics systems can be used as backup engines as well, if the combustion engine breakdown to reach the riverbank.

You must know that actual electric engines that have a high and almost constant torque have a much better output than their thermic counterpart.

How to choose your electric motor ?

Before searching to know which engine you should choose, you must know few things :

  • The weight of your craft
  • The weight of the equipment on board (laden weight)
  • The weight of the passenger(s)
  • The dimension of the boat

Those measures will give you the keys to identify your needs in terms of power. We will come back to this later.

How to set-up an electric engine ?

Set-up at the sern Set-up at the prow

Illustration tirée du catalogue Minn Kota

Illustration tirée du catalogue Minn Kota


How powerfull should be my electric motor?

We usually measure it in pounds (lbs) or Kw but not horsepower.

Note : Some electric motors, especially from the Torqeedo range, reach a 8 hp (horsepower). It’s clearly enough to substitute any thermic motor in a calm water environment. Even if the electric didn’t reach the performances of thermic motors, the gap tend to disappear, thanks to plenty of innovations.

  • Equivalence
Power Equivalence in horse power Utilisation
32 lbs 0.40 hp Small boat and dinguy


45 lbs 0.60 hp Zodiak, small boat : can be used as a harbour motor
55 lbs 0.80 CV Boat from 400kg and less. Can be used as a backup engine
86 lbs 1.5 CV Boat that weight less than 600 kg, Can be used as a backup engine as well.

If you want more equivalences, you can use this online converter.

For information :

  • Our ACE model is set-up with a 650w motor (approximately 0.9 hp)
  • Our SCOOP and SENSAS models are set-up with a 1.6 Kw motor (approximately 2.2 hp)
  • Our Most model is set-up with a 2.2 Kw motor (approximately 3 hp)

What self-sufficiency should have my electric propulsion system ?

We can not talk about electric motors without talking about range or autonomy of the battery. If you want an over powered motor and if your battery is not adapted, you might be able to steer fast but during an extremely short time.

It is a determining factor that is, unfortunately, not visible or not understandable during the purshase decision. Indeed, the consumption of your electric motor will depend on the use you make with it : do you want to go full speed nonstop ?

In this case , rather have a backup battery on board because the autonomy will be largely reduced comparatively to a normal use of the motor.

Before looking for an electric system, think about your real need and the use you will have from your electric motor : do I need a lot of autonomy ? Do my electric consumption is important (high speed) ? Will I steer in calm areas or will I have to front tough conditions ?

Explanations :

Battery type The power The autonomy of the battery
  • Lithium batteries (low weight, practicle but expensive)
  • Lead acid batteries (usually cheap but be carefull to deep discharge)
  • The Gel batteries (low lifespan)
  • Measured in Ah (amperehour)
  • Reminder : The amperehour is the quantity of electricity crossing a conductor section from a 1 ampere intensity power for 1 hour.
  • This is to say : The autonomy is dependant from the power consumed by your electric motor and the capacity of your battery.
  • The calculation is : Power of the battery / used power.
  • In this way, for an electric motor from 55 lbs and using 70 ampere (on maximum speed) supplied by a 80 Ah (lithium battery), we will get a 1 hour and 9 minute autonomy (80/70=1.15)
    • Warning : with a lead acid battery, you must keep a minimum of 20% charge or you will fall into deep discharge, destroying your battery irreversibly. So we have a real autonomy of 55 minutes (80*0.8=64, 64/70=0.91, (0.91/100)*60=55 min)

 : Do not exclude the weight of the battery, for exemple to supply our SCOOP, a 4 battery pack is necessary (an extra 200 kilograms on top of the boat weight !) The weight is a really important variable).

You can find all our battery and equipments here.

Note : 

  • With a variable voltage regulator you can reach a 50% energy economy. Moreover, the regulator ensure a better functioning of the system but impact the total price.

How fast is an electric motor ?

According to the use of each of us, the maximum speed might be the less important factor.

Usually, for a river or waterway use, the speed is limited to 4.9mph in France : useless to have a powerful boat.

Some electric motors are particularly powerful and enable a sea use of the boat with much higher speed. However those motors are rare and more expensive. For example, the Bruce 22, set up with a UQM Power phase Pro 100 with a maximum power of 100 kW reach a 65km/h speed

  • If you are not convinced yet to go electric, do not hesitate to check all our motors and equipment.
  • If you have some questions about electric motors systems, do not hesitate to contact us, our team will be pleased to answer you !

1 commentaire

  1. Peter Hutchinson says: ,  

    I’ve been using a Bison electric outboard on my Drascombe Longboat for about 3 years. In theory, this 1100 watt motor provides 100lb of thrust at full power and burns around 50 amps from a 24 volt system. Though undersize for the boat, which weighs around 1250Kg, around 3 knots is possible in calm conditions. The 120 amp hour lead acid batteries provide about an hour at full throttle, or about four hours at the minimum setting, which burns 21 amps. At present, the very high cost of lithium batteries rules them out, but they would be a better choice, giving greatly increased power density for thier size and much lighter weight, as well as a less critical state of charge sensitivity. In an ideal world, lead acid batteries should not be discharged by more than 50% on a regular basis, and must be recharged at once to avoid sulphation which will reduce capacity. I use solar panels to do this whilst the boat sits on the mooring. The system is therefore self sustaining and suitable for auxilary power when not using the sails. However, a conventional outboard would be a better choice as a primary power source, as an electric system can’t produce the thrust and range of a 5hp petrol engine. In the long run, high capacity graphine batteries may solve many of these problems, but probably not for the next 10 to 20 years until fully developed at a reasonable price.

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