Electric jet boat motor or electric outboard motor- which is best?
How to choose an electric boat motor.
The popularity of electric boats has increased significantly over the last few years and up until recently, electric outboard motors have been the default choice of boat motor for many electric boat buyers. However, due to rapid advances in technology, there are now more types of electric boat motors on the market than ever. This leaves many electric boat buyers wondering if outboards really are the best option to invest their money in? This guide will cover an introduction to electric boat motors and compare electric jet boat motors with electric outboard motors:
Who is this guide for?
There are many types of boats on the market which are electric-powered (see our Electric Boats article for a sample). This guide is for electric boat buyers who are looking for a versatile new electric tender or electric RIB around 3-5m long to service their mothership including short trips to the shore and back, or for leisurely activities such as fishing in the harbour, watersports and swimming, or to explore the surrounding waters. There would need to be a good amount of space on the tender to accommodate friends and family as well as supplies.
For a more detailed guide on features and considerations when buying an electric boat, please refer to our article: Electric Boats- a Buyers Guide.
Why buy an electric boat?
Compared to petrol and diesel-powered boats, electric boats are significantly better for the environment and require less maintenance. They deliver a more enjoyable ride due to no loud engine noises and no noxious fumes, as well as faster acceleration and instant torque. Plus when you spend hours out on the water, they save you the huge fuel costs! To learn more about why you should choose an electric boat over a petrol or diesel-powered boat please see our guide on ‘Why you should choose an electric boat over a petrol or diesel outboard motor.’
Types of electric boat motors
Electric boats are either propelled by a water jet, outboard, inboard, a sterndrive, or with surface or pod drives. Similar to combustion motors, an electric boat motor is often classified based on how the motor system is mounted on or within the boat. There are 2 broad categories:
Outboard
Inboard
The electric boating industry is still in its early phase, and while many types of electric outboard engines have been released, there are also a number of inboard motor options which have been launched over recent years.
Outboard boat motors
An outboard boat motor refers to a boat’s power system where the motor is located outside the hull of the boat. It is designed to be mounted on the transom (stern) of the boat. The typical small electric outboard has the motor, propulsion and batteries located outside of the hull in one single self-contained unit. Larger electric outboards require batteries to be located elsewhere in the boat.
Outboard propulsion types
Propeller-drives, surface drives and jet-drives are propulsion types that can be used with a motor located outside of the hull, with the most common type of outboard propulsion being the propeller-drive, where the rotational motion of the motor’s drive shaft creates thrust to propel the boat forward. For this article when we refer generally to electric outboards, we are referring to these propeller-driven outboards.
Inboard boat motors
An inboard boat motor refers to a boat’s power system where the motor is located inside the hull of the boat. Inboard boat motors are permanently fixed and cannot be easily moved from boat to boat.
Inboard propulsion types
Surface drives, stern drives, pod drives and jet drives are all propulsion types that can be used with a motor located inside of the hull. For this article we focus on inboard electric jet drives and use these for the comparisons.
Comparing inboard electric jet boat motors and electric outboards
In this guide we compare electric jet boat motors and electric outboard motors as these better suit the requirements of small electric tenders or electric RIBs compared to other types. For example, stern drives are not as effective in shallow waters and can be less maneuverable, pod drives can protrude a long way out from under the boat, and surface drives have limited capability in rough water and can be more susceptible to damage than other types.
How does an electric jet boat motor work?
An electric jet boat motor works in a 5-step process:
The electric motor converts electrical energy from the battery into mechanical energy.
The mechanical energy powers the impeller which has rotating curved blades that draw in the water through an intake located near the bottom of the hull and accelerate it.
A stationary component called a stator then straightens and smooths the flow of the accelerated water.
That water is then passed through a nozzle, creating the high-velocity jet stream that thrusts the boat through the water.
The steering system deflects the flow from the nozzle which allows the driver to change the direction of the water jet and therefore allows the boat to be steered.
Advantages of electric jet boat motors over electric outboards motors
There are a number of key benefits of electric jet motors when compared to electric outboards.
Electric jet motors can deliver higher performance
Faster acceleration
For small boats, electric jet boat motors generally provide faster acceleration than electric outboards because they respond faster to throttle changes. There are three reasons for this:
Jet impellers are often smaller than a propeller of equivalent power so spin faster for the same input.
Their smaller diameters make jet impellers less prone to cavitation (which reduces efficiency and damages blades) under heavy acceleration, compared to the larger propellers required for equivalent outboard applications.
The typical electric outboard motor has a gearbox located between the motor and the propeller, whereas leading electric jet boat motors such as the ZeroJet models do not, so the mechanical energy can be transferred directly to the impeller, reducing inefficiencies between throttle changes and propulsion output.
So, when the throttle of a well designed electric jet motor is engaged, the boat will simply blast off! Additionally, unlike electric outboards, electric jets generate more thrust the faster they go so a jet boat will typically manage to maintain a slightly higher speed as well.
Performance at speed
Electric jet boat motors deliver greater performance at speed because as jet-powered boats get faster, the inlet pressure increases, allowing the impeller to spin faster with less efficiency losses. This leads to a higher jet exit velocity than would otherwise be achievable at high speeds, in turn creating more thrust, and propelling the boat faster. Electric outboards encounter more resistance at higher speeds due to propellers and drive legs creating drag as the boat moves through the water, while with jet drives being internal to the hull, less resistance is created. For this reason, electric jets are also more efficient at higher speeds than outboards, requiring less power to achieve the same desired speed.
The typical small electric outboard is limited in power (measured in kW) to reach high speeds because the required batteries are limited by size as they have to fit within the single unit housing outboard attached at the stern of the boat. Larger electric outboard motors require the batteries to be installed elsewhere in the boat.
Electric jet motors are more practical and versatile than electric outboard motors
Operating in shallow and rocky waters
Unlike electric outboards, electric jets do not have low-hanging propellers that require a deep draft. They are streamlined and have a low profile, making them really easy to beach and well-suited to shallow waterways and rocky areas. No more wet pants walking from an outboard-powered boat to shore!
Easier to transport, stow and store
Electric jets are also more compact due to their low profile so you could fit a bigger tender in the same size garage, more equipment in the same garage, or choose to have a smaller tender garage, saving money on the build of your mothership or allowing more space on board for you to enjoy it.
With no large external outboard motor, electric jet tenders are easier to transport and move on and off larger yachts or launches. This includes stowing them in tender garages or hoisting and suspending with davits on your larger boat.
Easy maintenance and higher reliability
Electric jets use simplified engineering- they do not have a propeller, gearbox, lower unit, steering mechanism or exposed electrical connections. This means fewer moving parts than outboards, which is the reason for their lower maintenance and high reliability.
Additionally, outboard motors can suffer damage to the propeller, motor and drivetrain as the propeller can strike and entangle with underwater objects such as rocks, logs, mooring lines, and fishing nets during use.
Electric jets still require occasional maintenance. The impeller of electric jets can suck up debris such as seaweed, but quality electric jet systems are designed with grates over the intake to prevent larger debris from being ingested.
Electric jet motors are safer
Less risk of injury
Unlike outboards, electric jet boat motors do not have an exposed, fast rotating propeller so there is less risk of harm to boaties, swimmers, reefs or marine life.
Precise steering, agile turning, and easier maneuverability
Electric jets offer more precise steering and easier maneuverability than outboards, making jet-powered boats easier to handle. Plus you don’t have to worry about the metal shaft or propeller of an outboard motor damaging your mothership.
Typical electric jet boat motors are controlled by a rushing jet stream with low resistance, unlike outboards that use propellers which can create drag at the stern of the boat. Similarly, because there’s no lag time between throttle changes and propulsion output, electric jets are able to make agile turns and precise changes in direction and speed at both low and high speeds. This is important in situations such as avoiding boats, swimmers and other obstacles regardless of the speed the boat is travelling at.
The maneuverability enabled by electric jet boat motors also lets the driver make quick agile turns to create an exhilarating ride, which has been described by ZeroJet users as having a movement similar to ice skating!
Electric jet boat motors have a more beneficial configuration than electric outboards
Fewer energy losses
The configuration of electric jet boat motors lead to fewer energy losses than that of electric outboards, enabling jet-powered boats to get more on a single charge with less wear and tear.
This is because inboard electric jets are able to have a direct drive configuration without the motor getting in the water flow path, which would create increased drag. A direct drive system is beneficial since it does not require a gearbox, enabling the mechanical energy from the motor to be transferred to the propulsion unit with very few losses.
On the other hand, electric outboards with direct drive require the motor to be attached to the bottom outboard leg in order to be in line with the propeller. This places the motor in the water flow path, creating excess drag and causing inefficiencies and limiting the use of direct drive outboards to smaller motors and lower power outputs. For this reason, most electric outboards do not have a direct drive configuration, instead using a gearbox with the motor located at the top of the shaft. While this allows for a bigger motor and greater power outputs, it raises the center of gravity and leads to gearbox inefficiencies.
Better weight distribution
Since electric jet boat motors are inboard, the weight of the motor is closer to the center of the boat giving a lower center of gravity, and the weight distribution can be fine-tuned by the manufacturers. Proper weight distribution is important as it can not only improve the boat’s stability and handling, but its overall performance. For example, since it can reduce resistance, the boat can travel more smoothly through rocking and rolling sea conditions without consuming excess energy. It also improves safety since the boat is less likely to capsize or tip backwards without the need for stabilisers, trim tabs or handle extenders required by some electric outboards to combat this issue.
Already perfectly tuned for the boat
Unlike many outboards, inboard jet boat motors are bought already installed within the electric boat, where the combination of the boat and motor has already been tuned and tested before hitting the market. A perfectly tuned motor to boat combination is really important for many reasons. For example, if the motor is too small for the hull size and weight, it can take too long to plane and struggle to get up to the required speed.
If the motor is too large for the boat, you risk excessive speed and safety issues such as instability, capsizing and sinking. Additionally, if a motor is not tuned to the boat, it will have to work harder than necessary, leading to more wear and tear, frequent repairs and replacements, and as a consequence, a shorter lifespan.
Advantages of electric outboard motors over electric jet motors
Electric outboard motors can be cheaper up-front than electric jet motors
Electric jet boat motors tend to be more expensive upfront than electric outboard motors due to the additional design and internal boat components required for an electric jet propulsion system.
Electric outboard motors can be added to many existing boat designs
Basic electric outboard motors (up to 20 hp equivalent power) are made to be mounted on the transom of most boats, so they can be bolted onto the back of many small tenders on the market instead of a combustion engine. However, as the electric outboard motor and the boat hull haven’t been designed together, the combination may be an imperfect match which can negatively impact reliability and efficiency.
Gone with the Wynns test the “5 best electric boat motors.”
Why you should choose an electric jet boat motor over an electric outboard motor
If you’re able to look past the higher up-front price, there are many advantages to choosing an electric jet boat motor, and the benefits increase over time:
Electric jet boat motors offer better safety as there’s less risk of injury to people and wildlife as they have no exposed propeller. Plus, they’re better at avoiding obstacles due to their easy maneuverability.
Electric jet boat motors deliver higher performance because they accelerate quicker and have precise steering and agile turning which deliver an exhilarating experience. Plus, they can often deliver a higher top speed because the faster the boat is going, the more thrust is generated.
Electric jet boat motors have a more beneficial configuration resulting in fewer energy losses compared to electric outboards, and their inboard motor offers better weight distribution leading to greater performance and a well tuned motor to boat combination.
Electric jet boat motors offer greater practicality because of their streamlined nature and inboard configuration, enabling them to have more usable space on the boat, to operate in shallow waters and to be easier to transport, stow and store. Plus, due to their lack of moving parts, they are lower maintenance.
Before investing in an electric boat, make sure to get the best value for money by researching how options compare as a total package. In our article ‘Electric boats for sale- a buyer's guide to going electric’ we give you an actionable guide of what to look for in a small electric boat. If you can choose the right electric boat motor you can not only have a functional boat ideal for your daily needs, but an exhilarating water toy for fun with family and friends!
ZeroJet is a pioneer of zero-compromise boating and manufacturer of electric jet propulsion systems, powering a range of electric tenders and RIBS across the globe. The ZeroJet Gen2 system has achieved sustainability, safety, practicality, and performance in one compact package, making it a world-leading marine propulsion system.
About the author:
This article was written by Stephanie Kingsford in collaboration with ZeroJet’s team of electric boat and electric jet system experts. Steph is a strategic communications specialist with a decade of experience advising and collaborating with companies on sales, marketing and communications. She and her family are based in the wonderful Waikato region of New Zealand.