Installation of an electric inboard motor in the boat 🛠️

The customer's boat is an Ohlson 8:8 (extended version of the hull). The boat was built in 1978 by the Karlskrona Varvet shipyard and designed by Einar Ohlson.

The boat has a weight of 3,300 kg, an overall length of 8.8 m, and a waterline length of 7.3 m. Theoretically, this results in a hull speed of about 7 knots, or 12 km/h.

The owner desired a purely electric range of 30 nautical miles or a travel time of 8 hours at a speed of 4 to 5 knots.

According to the calculated theoretical driving curve, a continuous power of around 2 kW per hour is necessary for a speed of 4 knots. For a speed of 5 knots, it is already around 4 kW per hour. Here, the exponential relationship between consumption and speed is very clearly visible.

In summary, for the customer's requirements of 4-5 knots, a motor with 4-5 kW of power should actually be sufficient. However, to keep the boat maneuverable in wind and weather, a 10 kW motor was installed after consultation with the owner - especially since two batteries were needed for the desired driving time and the additional cost of the motor itself is not too high. With the 10 kW electric motor, the 12.5 kW diesel could be adequately replaced.

Before the conversion, a Volvo Penta MD7 with 12.5 kW (17 HP) was installed. The boat was driven with a 14x9" 2-blade propeller

The propeller is a key component in any drivetrain. Even with an electric motor, it is important to have a modern and efficient propeller that is well matched to the boat and the motor.

Together with the customer, we decided on the Bruntons Autoprop, which was recommended by a specialist's calculations as the best solution for this project. The installation of the new propeller led to minor delays, as we had to slightly modify the hull and the rear keel to optimize the water flow and avoid cavitation. But the result was worth it!

1. Planning and Measurements

For the installation of the motor, batteries, and other components, good planning and accurate measurements are important. Since every engine compartment is different, we took the time to ensure that the motor fits. In most cases, however, the electric motor should fit without any issues. If not, one can use another motor or adjust the engine compartment.

2. Removal of the Old Diesel Engine

The removal of the old drivetrain (engine, cables, hoses, and fuel tank) took about half a day and was one of the easier tasks. Emptying the fuel tank beforehand prevented leaks and fire hazards, especially since tools like grinders can generate heat and boats contain many flammable materials. Safety should always be the top priority in boat building! We worked very carefully during the removal and used a crane to safely lift all parts out.

3. Preparation for Installation
First, we thoroughly cleaned the engine compartment and removed oil and fuel residues from the last 30 years. The approximately 30 minutes of work make a big difference in the end.

Then came the moment of truth: We had to check whether measurements and plans were correct. Unfortunately, some dimensions in the drawings were incomplete, so we had to expand the engine compartment between the foundations of the engine mount.

Since the engine compartment was a bit short, the controller also had to be installed independently of the engine. All in all, we spent about half a day here - a bit longer than planned - but that can happen with such individual projects.

4. Aligning the Motor

The preliminary alignment was a relatively quick step with the right tools. Precision is crucial - the tolerances for aligning the coupling flanges had to remain within 0.1 mm. Since I had already performed many alignments, I only needed 20 minutes. However, for beginners, it is advisable to take more time.

5. Installation and Final Alignment

The next step was to mark the positions of the motor mounts. In many cases, new holes had to be drilled and threads cut. If one has no experience with this, it is advisable to consult a professional or seek the help of a mechanic. The threads had to be straight through the iron.

We checked the alignment at every step, as the motor could shift when tightening the fastening screws and needed to be realigned. This final step could be frustrating, so patience was required. An experienced mechanic needs about 1 - 1.5 hours for this.

6. Installing and wiring the batteries

The placement of the batteries was crucial for safety. Ideally, the batteries should be installed in a sealed (but ventilated) compartment. The batteries from WaterWorld are particularly safe and well protected against fires due to the LiFePO4 technology and their aluminum housing.

At this stage, it was important to ensure an even resistance in the positive and negative cables when connecting two or more batteries in parallel. The right balance guarantees equal charging and discharging currents, which extends the lifespan of the batteries and minimizes operational errors. We only used high-quality components such as rails, fuses, fuse holders, cables, and cable lugs.

7 Connection and setup of the system

Reading the manual in advance was a great advantage. The drive from WaterWorld has been one of the easiest systems to install so far. Especially when using a complete WaterWorld system, hardly any errors are possible.

Since I have worked in a professional boat building workshop on several electrical boat systems, I can confidently say that the WaterWorld system is far superior to others.

With other systems, there were often compatibility issues due to components from different manufacturers, which led to delays in troubleshooting. In contrast, the WaterWorld system was plug-and-play, making installation quick and easy. Once the hardware was in place, we only had to check if the battery was set to CAN, and the system was ready.

The best moment was when we turned the key, pushed the throttle forward, and heard nothing. The transformation of the boat was incredible, with quiet yet powerful performance. The sea trials confirmed that our calculations were correct, and we even exceeded the estimated range of 30 nautical miles.

The new propeller significantly improved the boat's performance. Compared to the old diesel engine, maneuverability was better and the turning radius was smaller.

Our customer put it succinctly: 'Now I can turn my boat with a coin.' Overall, the performance of the boat with the new engine was excellent, making the conversion a complete success.

Display & throttle were very easy to operate thanks to the plug & play connection. Effectively, only the appropriate communication cables needed to be plugged in.

Shore connection with circuit breaker: A shore connection for power intake in the marina was installed on the boat. Inside the boat, the line goes to a connection box with a circuit breaker. The chargers for the 48V network and the 12V network are located behind it with a suitable damp-proof socket.

Wiring & fuses: It is important to calculate the correct cross-section depending on the length of the cables. In addition, fuses should be installed inside the boat in case of overcurrents. A main switch is also recommended within the circuit.

This project was about much more than just replacing a motor. Due to unexpected complications and additional work that went beyond a standard electrical conversion, it took a whole work week.

Under ideal conditions, the installation of a WaterWorld system should not take longer than two days - depending on the size of the boat and additional features.