If you’re new to electric boating, have a read through our FAQ which providers general answers to some basic questions you may have:
- History of Electric Boating
The first electric boat was developed by a German inventor around 1839 and a small electric outboard was first patented in 1880 by a French engineer. From that moment until the 1920’s electric propulsion was very common with many boats in operation on lakes and rivers in the UK and USA. The advent of the internal combustion engine led to a steep decline in electric propulsion for boats, with a few exemptions like submarines.
A revival started in the 1970’s when the Duffy Electric Boat Co started mass-producing small electric boats in California, USA. Legislation has seen an accelerated uptake for both commercial and recreational use since the early 2000’s particularly in Western Europe, hence many leading brands originating there.`
- What types of boats are best suited for electric?
Please read our comprehensive article on this topic here: Is electric propulsion suitable for my boat?
Generally speaking, slow-traveling boats such as displacement craft (classic motor boats, yachts and trailer-sailers) are suitable to convert to electric, as well as light multi-hulls, dinghies, tenders and kayaks.
- What types of boats are NOT suited for electric?
Generally speaking, the biggest limitations are related to speed and range. In order to make a boat go only a little faster, exponentially more energy is required. For that reason (in most circumstances) speed boats are not suitable. Also any boat where a long range is required (over 8 hours of motoring per day) is less suitable, particularly if there is no provision to re-charge from shore power overnight (ie if the boat is kept on a swing-mooring).
- Are electric motors and boats expensive?
Whilst generally speaking, the upfront investment for an electric inboard or outboard including batteries is higher than a comparable combustion engine, prices of both motors and batteries have come down in recent years due to a dramatic increase in global demand and production as well as technological advances. Converting an existing boat to electric, or buying an electric boat is now a viable option for every boating enthusiast or commercial operator.
- What are the benefits of electric boating?
The decision to go electric can be based on reasons that are different for each boat owner or operator, but some of the main benefits are:
- – User experience: Quiet and vibration free, no exhaust fumes and fuel smells, max torque at any speed/rpm
- – Reliability: little maintenance required due to the small number of moving parts
- – Cleanliness: no oil and fuel leaks into the bilge or waterways
- – Safety: no flammable fuels onboard
- – Cost saving (particular for commercial operators): higher efficiency than combustion motors, reduced fuel and maintenance cost
– Environmental: no pollution into the waterway, opportunity to re-charge from renewable sources such as solar and wind energy, not scaring away wildlife, see more info here
- How efficient are electric motors?
- – Many electric motors have >90% efficiency: much more efficient than combustion motors
- – For displacement boats, highest overall efficiency is achieved by large propeller with a high pitch, that turns relatively slowly through the water
- – This ensures as little energy as possible is wasted. Some modern electric drive systems have an overall efficiency of up to 50%, whereas in comparison a petrol motor has an overall efficiency of less than 10%
- – Combustion engines need reduction gears. Because of the losses associated with gearing, many electric drives eliminate it by using low RPM, high-torque motors
- – On top of this, generating electricity at a large PowerStation is much more efficient than burning fossil fuels in a small motor onboard
– Research by the Australian Govt has shown that a small 2 stroke outboard can be as polluting as 50 cars covering the same distance! Read the research paper here.
- What size motor do I need?
The size of the electric motor is expressed as it’s power output in kilo watt (kW) The size of electric motor needed largely depends on how you wish to use your boat, conditions of your local waterway and the range and speed required. Due to the higher efficiency of electric motors, on displacement craft, 1kW of electric power gives the equivalent performance as 3hp of combustion engine power
1 kilo Watt (kW) = 1.34 mechanical Horse Power (hp)
However, in most instances (only applicable to displacement style craft) 1kW replaces 3hp!
- – no reduction gear
- – max torque at any rpm
- – minimal heat/friction losses (alternator, water pump, flywheel, etc)
- – electric motor can be overloaded where a diesel motor will stall
If current diesel performance is adequate: replace with 1/3 in kW (eg replace a 15HP diesel with 5kW electric motor)
If diesel power is unknown: displacement x 2 = kW rating of motor needed (eg a 3 ton boat would need a 6kW electric motor)
Size of motor depends on:
- – specific performance requirements of boat owner/operator
- – area of operation (sheltered water or open ocean)
- – corrections for hull shape and water line length (eg multihull or heavy monohull)
- How many batteries do I need?
Most small recreational electric boats operate at 24 / 36 / 48V
Larger (commercial) craft typically operate at 144V or higher
Minimum battery requirements:
2-3 hours motoring (auxiliary drive on yachts): motor kW x 1.5 = minimum usable battery capacity in kWh
6-8 hours motoring (motor boats): motor kW x 2.5 = minimum usable battery capacity in kWh
20′ sail boat (weight 1 ton) with 2kW electric outboard
2 x 1.5 = battery bank with minimum of 3kW usable energy (24V / 125Ah)
25’ motor boat (weight 2.5 ton) with 5kW electric inboard
5 x 2.5 = 12.5kW battery bank (48V / 260Ah)
- – For longer running times and/or higher speeds, more batteries are needed
- – When choosing Lithium batteries you will get more capacity from a smaller pack than with lead batteries
- Choosing batteries: The PROS and CONS of lead acid
High quality lead acids such as sealed AGM deep cycle batteries are most cost effective for most small/medium sized displacement boat applications.
Lead batteries last for approx 500 cycles over 10 year period (depending on exact battery model and depth-of-discharges)
- – Simple technology
- – Weight can be used as ballast
- – Relatively inexpensive
- – Big & heavy
- – Lose their charge over time
- – Can only be charged and discharged relatively slowly
- – Should not be discharged too deep
- Choosing batteries: The PROS and CONS of Lithium
In some instances Lithium batteries are desirable for their benefits over lead acid
Lithium batteries last for approx 2000 cycles over 10 year period (depending on exact battery model and depth-of-discharges)
- – Lighter & smaller
- – Deep discharge possible
- – Fast charging and discharging rates
- – More complicated technology, particularly bigger banks require sophisticated battery management systems (BMS)
- – Expensive
- – Safety issues with Lithium batteries that are not designed to be used in a marine environment
- Choosing batteries: Lead Acid VV Lithium
Lead-Acid and Lithium both have a life expectancy of approx 10 years max
In these 10 years a Lead Acid battery will offer up to 500 discharge cycles
In these 10 years a Lithium battery will offer up to 2000 discharge cycles
Lithium is generally 2 to 3 times more expensive than Lead Acid
If you use the boat a lot (more than 150 times per year) Lithium works out cheaper in the long run
As this is often not the case with recreational boats, the remaining benefits of Lithium are:
- – higher energy density (smaller & lighter battery)
- – very deep discharge with no harm to the battery
- – quick recharging
- – ideal for solar charging as Lithium batteries don’t mind sitting empty as much
If you have a displacement boat which needs weight: use lead acid
If you have a lightweight racing yacht and/or a big budget: use lithium
- What are the options to recharge my batteries?
AT THE MARINA = plug in to shore power 240V, fully charged overnight, ready to go again the next day
ON A TRAILER = plug into the mains at home 240V, fully charged overnight, ready to go again the next day
ON A SWING MOORING = use solar panels and/or (wind)generator. Generally 1 day of motoring (approx 6-8hrs) can be expected per week if solely relying on solar charging on a swing mooring.
- Cost indication for a complete electric drive system including batteries and charger
DRIVE SYSTEM EXAMPLES PRICE $
1 kW (3hp equivalent) electric outboard 3,520
incl 915Wh Lithium battery and charger
4kW (10hp equivalent) electric outboard 6,380
5kWh battery (Lithium) from 8,580
charger from 1,540 +
Total from 16,500
5kw (15hp equivalent) electric inboard 8,990
7.5kWh battery bank (lead-acid) from 2,990
charger from 875 +
Total from 12,855
10kW (30hp equivalent) electric inboard 12,990
20kWh battery bank (lead-acid) from 7,990
charger from 875 +
Total from 21,855