ELECTRIC BOATING

The theoretical range of an electric boat depends on three factors:

• Battery capacity is measured in kilo-watt-hours (kWh). The higher the battery capacity, the greater the range.
• The engine’s power determines electricity consumption. It is measured in kilowatts (kW). A 6 kW motor can easily operate at 1 kW and reach 4 knots, or at 3 kW and reach 5 knots, depending on the situation.
• Runtime in hours (h) is calculated by the ratio of Capacity (Wh) to Power (W). For example, if your battery stores 6 kWh and you run your motor at 1 kW, then your runtime is 6 hours (=6/1).

Solar cruising speed is the speed in knots at which a solar-powered boat can travel indefinitely using only its photovoltaic cells as a power source. It is easiest to measure when the battery is at 90% state of charge (SOC), so that the MPPT controllers operate at their optimal level. By extension, the battery is considered charged when its SOC remains above 90%.

Solar speed is not necessarily a limiting factor during day trips, especially when stopping at anchor is part of the fun, as this allows time to recharge the batteries. It is therefore possible to exceed the solar range speed, or even push the motor to its maximum power.

Thus, the “sailors” will enjoy, if there is no wind, a silent engine without vibration or odor, and without experiencing the heeling caused by the sails. The “motor-boaters” will realize just how soothing it is to no longer have to refuel, to forget the lingering smell of gasoline, while still enjoying the thrill of reaching over 12 knots depending on their choice of motor and battery. If they don’t plan to sail during the following week, they can return the next weekend to find their boat fully recharged on its own thanks to the sun.

Solar boating offers a new lifestyle: enjoying a meal free from exhaust fumes while sailing, or sitting on the bow with your feet in the water. Experience on the French Riviera has shown that this speed can reach 2 knots. Yes, a solar boat can be “the slowest in the world” yet still feature the most advanced technology.

Note that the captain’s experience is essential to ensuring the safety and comfort of passengers. It took our sailors several years to perfect this lifestyle by taking advantage of the table’s position at the catamaran’s center of gravity and the open bow at the front.

This is likely a unique experience to share with your loved ones.

Let’s look at a few examples:

• If your boat can reach 12 knots while consuming 20 kW and your battery stores 20 kWh, you can easily sail for an hour and push up to that speed a few times, as long as you make sure to return with more than 20% charge remaining. A sunny week following your return can charge nearly 40 kWh of energy!
• If you want to reach an anchorage 3 nautical miles away and your net solar consumption is 2.5 kW at a cruising speed of 6 knots in calm seas, it will take just 30 minutes to reach the anchorage, and you will have consumed 1.25 kWh. Let’s say you have a 5.4 kWh battery; it will show over 75%. You could recharge the battery to 100% in 1 hour at anchor in full sun at a temperature close to 20°C.
• If the weather has turned bad, and you prefer to cruise at 3 knots for the passengers’ comfort, your net solar consumption is likely 1 kW. At this speed, in one hour, you will have consumed 1 kWh of net solar power, and your battery will show just over 80%.
• If you opt for a 2-hour outing at 2 knots by night to cruise among the yachts of the French Riviera while enjoying a meal, the engine consumes 300 W without solar input because it is nighttime. Upon arrival, you will have consumed 600 Wh, and your battery will show nearly 90%.

An electrically powered boat requires less maintenance than any other boat. The maintenance of an electric motor can be as simple as changing a seal, provided you navigate according to the rules of the art. The endurance of SeaZen boats, in intensive rental conditions, proves that it works.

But reading dozens of manuals, covering all the components of an electric propulsion system, can be difficult to digest. In addition, maintenance technicians familiar with the multiple systems on the market are rare in ports. Given that even a minor problem can become critical, ‘Maintenance-Less’ means fewer gadgets, reliable engines, well-dimensioned batteries, and electrical components with remote support capabilities — especially valuable in remote areas.

Each motor requires varying degrees of maintenance, depending on its technology. It is essential to read the manufacturer’s instructions, especially to monitor the anodes.

With propeller

Propeller motors have a seal around the shaft, which must be checked periodically and preventively replaced by a service center approved by the manufacturer. On a daily basis, it is enough to regularly check the condition of the propeller and anode, and to make sure that no fishing line is wrapped around the shaft. These are the main sensitive points of these engines.

Without propeller

“RIM” engines have a propeller that rotates inside a nozzle, which avoids the maintenance of seals and even gearboxes. Depending on the technology used, it may or may not be necessary to check that the parts are properly lubricated. That’s all!

In all cases, the operating cost of an electric motor is very low compared to traditional internal combustion engines.

Several technologies are available. Lithium is particularly interesting because it allows you to save weight, which improves the energy efficiency of the boat.

Battery wear depends mainly on how you use it. The main indicators are the % of charge, sometimes called SOC (State Of Charge), and the ratio P between the power called by the engine and the maximum power that the battery can deliver.

Premature ageing of the battery is largely accelerated by the number of deep discharges and by the proportion to navigate with a P ratio greater than 1. Battery life is maximized if you always stay above 50% SOC and with a P ratio of less than 0.5.

• If you are sailing on solar power, it is quite possible that the batteries will fluctuate between 80% just before sunrise and 100% at noon. This is another advantage of a solar-powered boat: the batteries wear out much less
• If you always sail at maximum speed, it is in your interest to increase the battery capacity to aim for the lowest possible P ratio.
• If you do not have solar production and the boat remains unoccupied, it is imperative to turn off the electrical appliances on board, especially the refrigerator (optional). You can also control the SOC charge remotely (optional), which is recommended in case of prolonged absence.

A cognitive dissonance arises when motorboat enthusiasts, who value speed and range, realize that electric batteries cannot achieve the same energy density. This conflict between the pleasure of unlimited freedom on the water and environmental awareness creates a sense of unease. There are many such dissonances:

• Do I realize that in 80% of cases, I use my boat to travel less than 6 miles from the harbor?
• My magnificent boat, built for speed and the roar of its engines, will lose all its soul as it cruises electric at five knots… in silence.
• The capacity of the power grid is insufficient to support charging stations for the world’s recreational boats.

The hybrid (thermal + electric) offers flexibility and autonomy: it allows you to sail 100% electric (quiet, ecological and economical) for short outings, while keeping the combustion engine for long distances or power needs. This solution reduces costs, consumption and emissions, extends the life of the engine, and avoids “autonomy anxiety”. Ideal for a gradual transition to electric, without giving up the pleasure of navigation. It has a price, but it may be the only way to keep the charm of a boat designed to go fast, and be able to go to nature reserves that will gradually be banned from combustion engine or simply to save fuel.

A hybrid-electric refit requires less investment than a full-electric refit.

Few boaters are switching from sailing to motor-boating—or vice versa—because it represents a profound change in the way they navigate, rules, sensations, and habits. Switching to electric follows the same logic: it is a different boating practice. Those who try it are surprised: electric boating, with its silence, simplicity, reinvents the leisure of sailing. Without the noise or vibrations, you rediscover the sounds of the water, and a purer sense of freedom. It is a new way of life as far from motor-boating as sailing is.

Let’s keep it simple: full-electric boaters can choose between:

• A conventionally designed boat, refited or new, with a more limited range, so it will be a compromise.
• A hydrofoil boat with 40% more efficiency.
• A solar catamaran that avoids charging problems, cheaper than a conventional electric substitute, offering more usable deck space for the same length.