The "simple" values
The values length, width and draft seem to be self-explanatory at first glance in the electric yacht comparison, but you should not disregard the values. Does the port you want to enter offer suitable berths? If you want to dock at the beach, is the draft shallow enough to wade through the water to shore or do you have to dinghy ashore? You should have clarified these questions beforehand and internalized which values should not be exceeded.
How big should the water tank be?
The average fresh water consumption is about 130 litres per day. This means that the water tank on board should hold at least 130 litres times the number of people times days without fresh water access. For 6 guests and 2 crew members this is already 1040 litres for a day trip. If you are planning longer trips, you should make sure that the electric yacht has a water treatment system.
Range
In the case of reach, not only is there no uniform standard of measurement, but the specification is neither mandatory nor clearly defined. Furthermore, the manufacturers do not specify whether the range is achieved fully electrically or with the support of the generator. But also the indication as “all-electric range” without an average speed is problematic, because all yachts have a photovoltaic system on board, this generates electricity even in bad weather conditions. This means that a solar yacht only has to adjust its speed to the power generation in order to be underway at all times using only the all-electric drive. This can be done very slowly or with the help of an optional kite. Therefore, the value of the range is not particularly meaningful without a uniform standard of measurement.
What should a uniform measurement standard for range look like?
A standard is needed for comparability of all-electric range. FHowever, there is no uniform measurement standard for the range of electric yachts. In the case of e-cars, there are several and we would at least like to see a standard for yachts with fully electric propulsion. This standard should be the average speed and the average solar radiation on the photovoltaic system (so that the efficiency of the systems can be compared). Far away the weight should be as uniform as possible and it should be tested with full fuel and water tanks. Once the standard exists, you can compare electric yachts based on their efficiency. Especially for potential customers who place a high value on sustainable reach, a measurement standard should be extremely relevant.
What's the deal with displacement? and why is this an important value for the range of an electric yacht?
The displacement should first of all be equal to the mass of the ship, because if the mass is greater than the displacement, the yacht will sink. This is based on the Archimedean principle. That an electric yacht should not sink is already a basic requirement for a good yacht, however, the value is therefore not particularly important, but with the water displacement you can theoretically calculate the maximum speed and the maximum range.
What does the unit of measurement kWp mean for solar cells?
The suffix p in the usual kW (kilowatt) specification indicates how much electricity can be generated at peak. A four person household needs about 4-5 kWp. A household does not usually move and consequently does not require electricity for propulsion. With an electric yacht, the need therefore looks somewhat different. How much is needed here depends largely on how you drive. The value also depends to a large extent on the efficiency of the cells. This means that a yacht where the hull is full of solar cells does not necessarily have to have more kWp. With a high kWp, a lot of power flows either into the batteries or directly into the electric drive. Therefore, a higher kWp value is better for long distance with the all-electric drive.
How is the area of solar cells converted into kWp?
How many kWp a solar cell surface has depends largely on the performance of the cells and the weather conditions. In best conditions the value is 5-8m²/kWp, in bad conditions the average is about 14m²/kWp. We have taken a value of 7m²/kWp for our conversion, because the efficiency of photovoltaics on yachts is better than on land, among other things due to the water reflection. On land, 10m²/kWp is usually taken as a guideline.
How much KW should the electric drive motor have?
Determining this value is particularly difficult. A good value for orientation is the maximum speed possible with the engine power. If this speed corresponds to the own driving behaviour, then the kW value is sufficient. However, if you like to go up to 20 knots every now and then, you will have to choose the most powerful engine on the current models.
What should be the maximum speed of the electric yacht?
The maximum speed depends on the one hand on the electric main drive, on the other hand the indicated maximum speed is partly reached with the help of the generator. Of course, if this is a diesel generator, the sustainability aspect of the electric yacht is terminated. However, an optional kite can also be helpful in achieving speed.
How many kWh should the battery have?
This depends primarily on how far the distances are that they want to cover and what power the main electric drive has. If you want to travel long distances and need a powerful motor, you should choose the largest batteries, i.e. those with the highest kWh value.
What influence does an additional kite have?
A kite can replace a sail that is 10 times the size of the kite by efficient use of fully automatic control. This not only means that the range can be increased almost infinitely, but when the wind is strong enough, the electric drive can be switched off and the batteries are charged via the solar cells. Since a kite flies at an altitude of 70m to 140m, it cannot be used everywhere. Especially in inland waters the use should be avoided. Consequently, the optional kite only has a significant impact if you are primarily in coastal and marine areas.
What is the difference between kVa and kW?
kW(kilowatt) is the actual power, while kVA(kilo volt-ampere) is only the apparent power. The actual is the apparent power times the power factor. The power factor is theoretically between 0 and 1, usually this is 0.8.
Why is the kVa value given?
The kVa is used in electric yachts that generate electricity via a hydrogen generator and use it as a range extender. The value is not unusual for generators with alternating current and especially for hydrogen generators. The actual power would of course be better for comparison with diesel generators and if you multiply the kVa value by 0.8 when comparing, the hydrogen generator performs significantly worse. However, when you buy an electric yacht with a hydrogen generator, you get a truly sustainable solution. An electric yacht with a diesel generator is comparable to the wolf in sheep’s clothing. One could also speak of greenwashing, because with an electric yacht that extends its range via a diesel generator, there is a hidden conflict of objectives. On the one hand, the focus is on sustainable propulsion without CO² emissions, on the other hand, the diesel generator has to intervene when the low-emission electric motor has discharged its battery.
Conclusion
The value of the range is only relevant for you if you frequently want to cover long distances in a given time. If this is not the case, you should also take a look at the other values and evaluate your needs. If after buying an electric yacht you find that your evaluation does not match the real value, you do not have to worry about a big loss of value if you want to sell the yacht again. Because, like their counterparts on the road, electric yachts are extremely stable in value and you can move to a yacht that suits your needs with relative ease.
