Boats With Electric Propulsion:   THIS PAGE IS UNDER CONSTRUCTION.

Boats propelled solely by electric motors are becoming more and more common. There have been significant developments in electric propulsion and battery technology which has allowed going all electric to be more affordable and more practical. It has become common enough that ABYC has developed standards for electric propulsion systems, and recently the US Coast Guard has published a request for public input on whether some standards that apply to gas powered boats should also apply to electric power boats.

For more Information Contact ABYC at abycinc.org and purchase a copy of E-30 Electric Propulsion Systems.

Outboard Electric Propulsion: There are electric outboards on the market ranging from trolling motors which are less than 1  horsepower,  to much more powerful outboards such as Axopar 25 rated as 300 Horsepower.  11,000 Watts is about 15 horsepower. 300 HP is in the range of 220KW.  That O/B costs around $147K. (Price in 2024) and that does not include the size and cost of the battery bank to run it. So it takes a lot of watts to generate horsepower. As with gasoline powered engines,  how your engine performs is dependent on the size and weight of the boat, and the type of boat. Here is a link to a converter from Watts to horsepower. https://www.unitconverters.net/power/watts-to-hp.htm .  Electric drives have also entered the sailing world. Yanmar has a drop-in saildrive rated at 15KW, replacement for their engines.

 The more powerful the motor is, the more batteries you need to power it. This gets into battery banks, multiple batteries hooked up together in series and parallel to provide the voltage and watts, and the amp-hours to power the motor. The other consideration is weight.  If you use lead acid batteries, the weight can be considerable. If you use lithium batteries, the weight is reduced considerably.  But lithium electrical systems are more complex than lead acid systems. See Batteries.   

There are two categories to consider: Electric outboards, and inboard electric motors.

Inboard Electric propulsion:

Electric propulsion boats have been around a long time.  ELCO has been in business for 130 years (https://www.elcomotoryachts.com/) so inboard electric propulsion is nothing new. Even large commercial and naval vessels have used electric propulsion. It was called diesel electric. That is, generators were driven by diesel engines.  The resulting electricity was used to drive large electric motors which drove the propellors. Probably the most common use of this was submarines.  Today we call this a hybrid system. But electric recreational boats have almost always used batteries.  Until the advent of lithium batteries, this has almost always been lead acid batteries. This required long charging hours and added a lot of weight to the boat.  This resultted in restricted use of the boat, and slow speeds. The features of lithium batteries,  light weight and longer amp-hours, along with better design of small electric motors, has made it possible to power boats for much longer times and achieve much higher speeds.

Power Sources: (battery banks)  Battery banks are two or more batteries connected in series or parallel, to increase the amount of power available, or make it last longer. See https://newboatbuilders.com/pages/electricity3.html and https://newboatbuilders.com/pages/electricity4.html  to explain battery types and series/parallel circuits.

When planning for electric propulsion you need to learn more about electricity, because you will need to determine the size of your battery bank, and how long power will last.  So first I need to define some terms.

Volts and Voltage. Voltage is a measure of potential energy contained in the battery and is measured in volts. The symbol for volts is V.

Voltage is what drives current flow. The amount of current is measured in Amperes, often shortened to Amps, or milliamperes. The symbol for Amperes is A, or milliamperes mA. Batteries are also rated by amp-hours. 1 amp for 1 hour is 1 amp-hr.

The amount of power is measured in Watts. Watts are calculated by multiplying Voltage times Amps. V x A = W  1000 Watts is a Kilowatt written as kW.

When designing battery banks, the most important factors are watts and watt hours.  Watt hours is defined as the measure of how many watts can be used for how long. 1 watt for one hour is one watt hour. But since we are dealing mainly with KiloWatts,  (kW),  we are mainly interested in Kilo watt hours. Kwh = Volts x Amp-Hours. Kwh = V X Ah. 12V X 1 Ah = 1Wh. 12v x 1000 Ah = 1000Wh which equals 1 Kwh.

A kiloWatt Hour is how much work 1 watt per second can do in 1 hour (3,600 seconds). See A Tutorial on Electric Propulsion For Boats. https://boattest.com/article/tutorial-electrical-propulsion-boats.   But we are dealing with a thousand Watts, that is, 1 KiloWatt (1kW).  This is a measure of how many Kilowatts you can use per hour.  This depends on the Voltage, amperes, amp hours, and the Watts. It also depends on the type of drive system you have, the boats weight, size and type.

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