How to choose the right electric outboard engine

Back in 2009 it seemed there were fewer electric outboard engines available than fingers on one hand.

Jump forward to 2023 and you might have to watch your step, for falling over them on every corner of boat show stands.

The following are the key specification factors to look out for when making your choice:

Motor (kW)

Manufacturers will also give you a horsepower (hp) equivalent to help. Motor ratings start at approximately 1kW (1.5hp) and head upwards.

Manufacturers websites give information as to which size kW motor you’ll require for your boat.

Note the continuous rating (kW) to ensure the electric outboard motors will run all day if battery capacity allows.

Peak motor (kW) ratings usually allow for a short sprint burst only.

Battery capacity (Ah/kWh)

The electric propulsion revolution is fuelled by the battery revolution, which means the benefits of modern batteries give us range and speed.

Capacity is also directly related to cost. Consider the battery location.

Smaller outboards tend to have their batteries integrated and removable, while larger outboards allow connection to a remote battery bank that would be installed in a suitable location on the boat.

Integrated usually means you have the option to remove it, allowing you to carry it separately back home for charging just as you would with a jerrycan.

Remotely installed means batteries mounted in a locker or secured to the floor.

Remote installation equals greater options for capacity, that means you can go longer and/or faster for longer.

The best choice is for a system approach using the manufacturer’s own batteries resulting in a slick installation.

Sourcing your own batteries (third party) doesn’t always pay off, but certainly can mean lower initial investment.

Voltage (V)

Options start at 12V and run up to 48V. Expect outboards greater than 20kW (27hp) to have higher voltages.

Motor cooling

It’s worth noting that electric outboard motors which have their drive motor in front of the propeller do not use an external water-cooling system.

Motors that are mounted on top of the leg, beneath the cowl, will have a cooling circuit, pump and maybe a heat exchanger.

This will require a flush through with fresh water after use if you want to prolong its life.

User info display

This is like your fuel gauge and then some. A battery state of charge indication is the bare minimum you’ll want for electric boating, but consumption indication/motor power is beneficial and helpful.

This will enable you to understand the amount of power (kW) your vessel requires at a specific speed.

Some outboards have integrated GPS to enable a range calculation, which is like the icing on the cake.

Noise (db) and vibration

Or rather the lack of it! Electric outboards do actually make a sound and if the motor has a gearbox, then expect it to be a higher decibel level than one that is a direct drive design.

Electric outboards with three or more propeller blades will have the least vibration.

Shaft lengths

Props out of the water aren’t good. A rule of thumb is to ensure the top of the prop tip is 300mm beneath the waterline where possible.

Construction materials

Plastic is fantastic – durable, corrosion resistant and low weight, but it’s often a case of throwing away if a suitable repair cannot be made.

Repairs often require the electric outboard to be returned to the dealer.

Other electric outboards use stainless steel and aluminium in their construction, typically found in larger, less portable models.

Propeller type

You’ll note some electric outboard manufacturers are using a leg that you’ll find familiar – supplied to them from a petrol outboard manufacturer.

These typically allow a fit of an open hub style propeller, which is not as efficient as a propeller designed specifically for an electric outboard.

Open hub propellers are easy to find, and you’ll have a maximum choice of sizes.

Electric outboard manufacturers often offer an option to purchase a different propeller size.

In most cases, a standard prop will be included with your purchase.

Axial propeller types (shaft in the centre) are not the only ones available. Rim drives (hub less) are also very much now part of the offering.

These provide fantastic thrust, vibration, and safety benefits, but are not so commonly used for higher speed applications.

Rim drives also are a very neat design, in that the motor is in the casing.

There’s only one moving part and that’s the motor’s rotor, which has the blades attached.

Sailing boat owners should be aware that no folding propellers are available for electric outboards to my knowledge.

An electric pod drive might be an alternative if you want a folding prop.

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Mounting

Nearly all outboards have the standard transom clamps, larger models also have mounting bolts for a more permanent and secure mounting solution.

Charging

You’ll find a standard charger is included in your purchase, but this will only afford you a slow charge, typically overnight.

Faster recharge can be achieved with a manufacturer’s optional fast charger.

They are typically mains (AC) supplied.

UK dealers

Buying an electric outboard from a reputable dealership is highly recommended for service and peace of mind.

Most manufacturers are now represented here in the UK.

Pitfalls

Using third party batteries will require a battery monitor to gain understanding what state of charge (SOC%) your battery bank is at.

Consider outboard brands that can supply a complete system, for stress free ownership and use.

Regeneration

I don’t know of any electric outboard manufacturers that publicise propeller regeneration as a feature.

Some pod drives do offer this, however.

Maintenance

Note that most electric outboards are for general (recreational) use, with the exception of trolling motors, which are designed for short distance, and manoeuvring.

Trolling motors

These are typically super manoeuvrable and low weight. Recreational fishermen commonly use these motors, in addition to their main propulsion motors, to enable them to manoeuvre the vessel at super low speed and hold position with their main engine off and often tilted up.

Not all trolling motors are rated for constant use, so read the fine print.

Best used in rivers, harbours that are shallow and have limited current.

Pod drives

Fixed pods, which do not allow for rotation, are ideally used in conjunction with the vessel’s rudder.

When not in use it will create drag, which can be reduced if used with a folding propeller.

Where pods are great, is the reduced impact within the vessel. You can expect to see the fixing bolts and the cable, nothing more!

Steerable pods are often located through a rudder stock arrangement or bolted to the transom.

These drives are usually very simple in design, but are certainly more robust, with their torpedo-looking shape.

Pods can provide a propulsion solution for cruisers that look to cruise greater distances, such as coastal and blue water.

Remote steering

The smallest tender motors might not allow for this, so it’s worth enquiring before purchase. Standard steering cables or hydraulics are compatible with bigger electric boat engines.

Kill switch

Kill switches are often the lanyard type, working with a switch arrangement or a more modern magnet fob design.

Stop buttons are usually supplied with motors designed for sailing boats or motorboats with a deeper cockpit/helm position.

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