Basics about Electric Boats



version 1.3 / D. de Vries / all4solar Australia


Electric versus Petrol Advantages

Electric motors are much more energy efficient than petrol engines as they convert upto 90% of the input into

moving power. They are quiet and generate no hazardous emissions. The electric power required can be produced

with photovoltaic solar panels, which makes the system completely independent from any external energy source.

Electric engines are nearly maintenance free, do not need oil and have very few moving parts. They are available

in almost any size, from a small 12 V 0.5 HP outboard motor to an inboard engine with several hundreds of kilowatts.

Electric motors do not need oxygen like combustion engines and can therefore be installed even under water.


The only real disadvantage of electric motors is the power source. Conventional lead acid batteries are 90 times

heavier than the equal amount of petrol used for the same power output. But battery technology is improving fast

since a few years. The latest Lithium batteries offer an energy density which is up to five times better than the lead acid

technology. Lithium batteries also allow up to 3000 full recharges and are much more efficient.

Is my boat suitable for an electric engine

Basically every boat can be equipped with an electric engine. Even the smallest kayaks or inflatable boats can carry

a small trolling motor. The critical point is again the battery. Your boat needs to be able to carry the battery weight

according to your power needs. The initial financial investment is still higher, but you will be investing in the technology

which will move cars and boats in the future.

What is needed for an electric propulsion system

The motor (outboard or inboard)

Motor controller (mostly part of the motor)

Batteries – any 12 V battery lead acid battery is suitable. For 24 Volts you need two, for 48 Volts you need four

batteries to be connected in series. For lithium batteries we recommend to purchase a ready assembled block with the

voltage suitable to your motor.

Battery charger (from the grid) or solar charger. Always charge the whole battery block and not single units to avoid

an inbalance. So, for a 48 Volts motor and battery block, use a 48 Volts charger or solar panel with an output of  48 Volts.

This is always the nominal Voltage – the effective charging voltage is at 14.5 Volts for a 12 Volts battery or up to 58 Volts

for a 48 Volt system.

Watts = Volts multiplied with Amps / 24 Volts * 50 Amps = 1200 Watts

IMPORTANT:  Always use a fuse and a main switch when connecting the motor to the battery for security reasons. Try to

purchase a complete set with all included from you supplier if you are not a specialist.

If you want to know more - check our book in the webshop.



     For online calculations use our free  web – calculator:


all4solar ™ | Trinity Park QLD 4879 Australia | |



Basic questions for the implementation of electric boat propulsion


Electric boat propulsion is not “rocket science”, but without the correct setup and the suitable equipment

it won’t work. So take your time and answer a few basic questions which allow us to provide you a

workable concept.


__ Replace diesel inboard __ HP  __ sail boat __ motor boat __ multihull

__ Replace petrol outboard __ HP  __ short shaft __ long shaft __ direct shaft drive

__ New boat

__ Main propulsion system __ Trolling motor

__ Average motor power during operation __ 25% __ 50% __ 75%

__ Average hourly petrol consumption __ litres

__ Maximum weight of engine and tank (batteries) ___ kg

__ Boat weight (without engine / Tank / Batteries) ___ kg

__ Boat size length ______ cm    width ______

__ Grid power available to recharge batteries

__ Travel time / distance till back to charge connection

__ Charge with solar power required __ Optional generator as range extension possible

__ High end ac induction motor (completely maintenance free) __ DC motor preferred (cheaper)

__ Lead acid batteries AGM (37 WH / kg  -  600 cycles – 65% power output in 1 hour)

__ Lithium batteries  (90 WH / kg – 2000 cycles - >90% power output in 1 hour) – approx twice the price of lead acid