#4 The electric motor

When we finally made the decision to convert the boat into a self-sufficient sailing ship, we also had to change the propulsion of the boat. We wanted to live on wind, water and sun and for this the diesel engine had to be replaced for a cleaner drive. Five years ago, there were two possibilities for us that seemed appropriate for this. The first was an electric motor with hydrogen and the second possibility was an electric motor with lithium batteries.

Because five years ago there weren’t many similar sailboats, which also went around the world, feeding electrically, meant we still had a lot to figure out. This became part of Niels’ graduation project. Together with the company Holthausen from Hoogezand, the possibilities have been looked at. There seemed to be an opportunity to use one of the box boxes for the production and storage of hydrogen. But there were also complications. It took too much power to produce the hydrogen. With the amount of solar panels, windmill and the screw axle generator on board, the energy needed could not be generated. Also, the storage in large tanks had to take place under a high pressure. Because this is totally new to sailing yachts, the question was whether we would be allowed to enter ports with such tanks and equipment. Now, after two years of sailing, I’ve never had an inspection in the engine room so far, which makes me think it wouldn’t have been a problem. Anyway, it’s still a risk. During the graduation project, it became clear over time that hydrogen on board a 42-foot sailboat was not convenient. If there are ever people who will take this step, remember that salt really comes everywhere. Also in places where you don’t think it’s coming. So if systems are built in sailboats, make sure everything can withstand salt to prevent misery along the way.

In the end, we opted for the second option: an electric motor with lithium batteries. We were able to achieve this setup within the time available. The lithium batteries were good to build and the cost was significantly less. The first step was to calculate the size of the engine. Together with the company Mennens from Groningen, we did a tow test to see how much pull the ship had with the current diesel engine. Because the boat was virtually stillag during the test, we didn’t have the resistance of the water and air, but at least we knew something. In the end, after considerable arithmetic, it was stipulated that an engine of at least 10kW should have sufficient power to propel the ship during heavier weather conditions. This is considerably less than the 72hp diesel engine!

Draw test with Mennens

The electric motor has become a water-cooled drivemaster 15kW 48V from Bellmarine. Because the diesel engine was still working well, we chose to leave it in case problems occur along the way. We have built a parallel setup, where the electric motor has come to hang diagonally next to the diesel engine. Through two v-strings, the electric motor drives the pool on to the main axle. The v-strings are strained with two tensioners to get enough pressure on the v-strings. Thanks to the Paragon control on the diesel engine, which serves as lower and runs freely, we didn’t have to change much about the existing drive shaft. Only the main axle had to be shortened slightly because an extra poolie was added.


After two years of sailing we are still incredibly excited about the engine. We haven’t had any complications with the electric motor so far. Once the contact is turned over, the engine starts within a second. It doesn’t have to get hot and with a jibe or tack during bad weather, it pushes us through the wind with ease. We don’t hear the engine, which makes talking a lot easier while sailing. 

So far, we haven’t had to have any maintenance. Thanks to the large control cabinet, the engine can be completely adjusted to your own wishes. This is useful if you want a certain number of revs or maximum power. On the contact lock are two positions: an ‘eco stand’ and ‘full of power’. Usually we sail at 70-80 of the eco stand. Then the engine asks 2.5kW and we sail around 4 knots. We can make up to 9 knots, but this drastically limits the time we can sail, because this requires more electricity. 4 knots is indeed slower than the 5.3 knots we could get with the diesel engine, but usually we are in no hurry. If we do have to go faster in case of an emergency, we can do just fine with the electric motor. 

While sailing, the electric engine also generates energy. All we have to do for this is to set how much resistance we want to have in a certain number of tours. We adjusted this well along the way, so we now charge quite a bit of energy. We don’t turn the charging on until a speed above 5 knots, otherwise it slows down too much, because of the resistance combined with the waves. Above 5.5 knots it starts to generate really good energy, with the peak of 700W. Not bad for a fixed screw!

Since February 2019, our diesel engine is broken. Before leaving Panama for the Markiezen, we had it run for half an hour in the port of Panama, because this has to be done once a month, to preserve the diesel engine. When crossing 50 days, something seems to have broken down, while we didn’t use the diesel engine, which we still don’t know what it is. This means that we have been sailing without a backup diesel engine for a whole year now. We are positively surprised how easy this has gone and when we look back on last year we didn’t miss the engine either.

Is this going to be the future? Yes, we think so. An electric motor requires so little maintenance and sails so quietly, this is a step forward for sailboats. Tack-going and jibes in the middle of the sea are also easy when we adjust the electric engine.  If there is just too little wind to sail, the electric motor can also run at a low speed. A disadvantage, of course, is that a larger battery bank has to come on board. Important questions are: ‘which batteries?’ and ‘how many batteries are needed for optimal drive?’ I’ll tell you more about this next time!

Questions? Please email us to info@4greenfoundation.com

Link to the electric motor is here.


Electric throttle

Left Multiplus of Victron and right bellmarine Engine Controller

Top view of the electric motor

Fit and measure

Choas while on the job

Always rehisonboard during the job

Front view of the electric motor

Suspension of the electric motor

Hoist ing electric motor on board