Electrical Energy – Powering Your Boat Efficiently
Having power on your boat is happiness! From brewing coffee, cooking with an induction cooktop, to charging phones and enjoying a hot shower, electricity keeps life comfortable. Without it, things can get a little uncomfortable. Let’s keep the energy flowing for smooth sailing and happy living!
2/2025 Written by Chris & Su Wallace from Squid and Jelly's Great Adventure
Having power on your boat is like finding the secret ingredient to happiness! Whether you're whipping up a gourmet meal on an induction cooktop, turning your Instant Pot into a magical kitchen wizard, brewing that much-needed cup of coffee, or keeping your phone and laptop charged for all those important "Facebook or Instagram moments", electricity is your best friend. And let’s not forget the luxury of hot water for a shower - because nothing says "I'm living the dream" like not freezing your way through a rinse. When power’s missing, it’s like sailing with no wind - everything feels off. So, let’s get that energy flowing so you can enjoy all the creature comforts of life at sea!
Understanding How Your Boat Generates Power
We all know that power flows in and out, but let’s dive deeper to ensure you have more than enough.
First, let's cover a few key terms you should know:
• Power or Electrical Power: Instantaneous consumption to perform work usually measured in Watts. Most modern electrical devices will have a sticker listing the Watts, usually maximum Watts consumed by the device. Remember anything electrical that gets warm, is wasting your precious energy. Nothing electrical gets warm for free.
• Energy: This is power consumed or stored over time. Watt-Hours (Wh) or kilowatt-hours (kWh) is the typical units. This is how your power is billed from the electric company on land or at a marina. Think of 1 kWh as 100 Watts consumed for 10 hours (100 x 10), or 1000 Watts for one hour (1000 x 1), 10 Watts for 100 hours (10 x 100), or any combination that totals up to the same. On a boat we often use Amp-Hours since batteries are often rated this way. The key takeaway here is that Energy usage for our purposes involves time. The longer you use an electrical device the more Energy it will consume.
• Battery: A device used to store electrical energy.
• Voltage: Electromotive force or differential. Forget that part and let's simplify it for boat use, 12VDC (Voltage Direct Current) is what most boats have and this is the type that is stored in your batteries. 24V and 48V are less common options. 120VAC (Voltage Alternating Current) or 230/240V are the kind that you likely had at home. On a boat this can be created directly from an AC Generator or "inverted" from a DC source like your battery. An increasing number of boats are seeking home-style voltage.
Things that make POWER on your sailboat!
1: Alternator(s): These are mechanically driven by your main engine, so they consume fuel to generate electrical energy. A typical alternator is usually rated between 60-80 amps (720W - 960W), but these ratings are for cold, as in just started, and drop to about half as they heat up. They will heat up quite quickly since they waste about half of the energy as heat. As a result, most boats produce between 300-500W while the engine is on. To estimate how much power is available to charge your batteries, you need to subtract the energy being consumed.
Example: Alternator output 50A = 600 W. 600 W - 175 W consumption = 425 W available to charge your batteries. 425 W x 3 hours = 1.275 kWh saved for later use. However, moving energy around creates waste heat, so assume 10-20% will be lost along the way. So with 3 hours of engine run time, you will get roughly 1 kWh stored for later use.
2: Solar: Solar panels convert sunshine into electrical energy. They output DC voltages that can range from 18 - 50 VDC. It is necessary for almost EVERY setup to use a Solar Controller between the panel and your batteries. We use and recommend Victron MPPT controllers. The best part about solar is that they are silent and requires virtually zero maintenance and are extremely reliable. These are our favorite energy source! Once you design, install and configure, they create energy for many years for free. However the output varies greatly depending on location and weather.
Example: We have 5 x 435Wp (Watt peak) + 2 x 360Wp solar panels on our 40' catamaran. The output will vary greatly every second of every day during daylight hours. So you must make some assumptions using solar insolation for your area and you must install them as shadow free as possible. I also highly recommend one MPPT solar controller per large panel for maximum harvest. Our daily output is typically 8- 10 kWh but our output over the last two years with this setup varies from as low as 1.5 kWh all the way up to 17 kWh on great days. This is obviously a huge difference, so it is unlikely that solar will be your only source of energy. My advice is to buy and install as much solar as you possibly can, whether physical space constrained or budget limited.
3: Generator: Smaller boats may have a "suitcase" style generator. Honda EU2200i is the gold standard. We had one of those but downgraded to the smaller version, EU1000i. Whichever one you buy, you should consider this add on tachometer/hour meter. You must consider the safety and noise concerns of a portable gasoline generator. Noise travels far across flat water. Carbon Monoxide from the exhaust can be lethal. Gasoline vapors are explosive and very dangerous. Never store the gasoline or a portable generator inside your boat. Please don't take these concerns lightly!
Larger boats, typically 40 feet and above may have built in generators. These are usually diesel powered, safer and quieter, which your neighbors will be thankful for. They are also more efficient, meaning, more energy produced per gallon. The downsides are weight and cost. We removed our Northern Lights 6 kW model, with fuel tank, enclosure, battery, filters, long exhaust hose and associated parts. It was at least 600 pounds of gear that came off the boat. Compare that to about 50 lbs for the Honda Eu2200i.
Both types typically make 120 VAC (230/240 V AC) which powers some items directly like an electric oven, water heater/boiler or even your blender. To charge your batteries, you will need a battery charger. We use and recommend Victron 50 Amp charger. Larger generators will require larger chargers or multiple chargers. Victron Multiplus Inverter/Chargers are what we use and recommend.
All generators require maintenance and can break down at really inconvenient times. So you will need spare parts and a backup plan.
Example: 6kW generator runs for one hour. Typically you want to load the generator up to 75-80% for long life. So you will want to make about 4000 Watts. From that you will want to charge the batteries and use the extra for heating water or cooking dinner, etc. If you have a "suitcase" generator you will likely have to run it 3 times longer.
SV Saguaro previously had a MarineKinetix MK450 Wind Generator but upgraded their solar system because they found it too noisy.
4: Wind Turbine/Generator: They convert moving air (wind) into electrical energy by spinning the rotating blades. However, the output isn't very high unless the wind is blowing at 15-20 knots or more. Wind generators are losing popularity, and I’m okay with that, as they tend to be noisy day and night. My recommendation is to use that space for additional solar panels instead. However, if you're in a windy and cloudy area, wind generators can still be useful. For smaller battery banks, generating power continuously is highly beneficial. But as boat battery capacities increase, this becomes less of a concern. Our favorite is the D400.
Example: 200-400W potential but likely averages 25 - 50 W x 24 hours = 0.6 - 1.2 kWh per day.
5: Hydrogenerator: These convert flowing water into electrical energy by rotating a propeller, similar to an underwater wind turbine. They are expensive and generate limited power. The ideal scenario for these is if you sail more than you anchor and at relatively high speeds (6-7+ knots). In that case, they can power all of your sailing instruments. However, most sailors spend more time at anchor or in marinas, where these won’t generate any power. Watt & Sea is the most well-known brand, and we would consider buying it if our usage case was different.
Example: Let’s be real - most boaters average around 5 knots while sailing. Depending on the model and propeller, that means an output of just 50-100W (about 1.2 - 2.4 kWh per day while sailing). Not exactly a power jackpot!
6: Fuel Cell: Methanol fuel cells convert methanol into electrical energy, but their output is relatively low, ranging from 40 to 125W. They are also quite expensive. These fuel cells are ideal for those who sail in areas with limited sunlight or wind. The main advantages are their compact size and quiet operation. EFOY is the leading brand for recreational marine use.
Example: 75W x 24 hours = 1.8 kWh per day.
7: Shore Power: This system uses the electric grid at the marina to charge your batteries and power your boat. The amount of electricity available is typically unlimited, though it's limited by the connections and how much you can use at once. While not much else needs to be said, the cost can add up depending on your location. Smart Plug offers the safest sockets, plugs, and cables, which we highly recommend. I've seen many connections and cables burn out, risking burning down the boat, so we trust and rely on Smart Plug Products for safety. Remember that you will still need a battery charger to charge the batteries as the shore power will be 120 VAC (or 230/240).
Having multiple energy sources on your boat is crucial for reliability and peace of mind. For us, that means seven solar panels with individual controllers, two engines with alternators, and a small suitcase generator- ten different sources ensuring we’re always powered up and ready for anything!
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Understanding how your boat generates, stores, and consumes energy is essential. While we all recognize that power flows in and out, you'll need to take a deeper dive to ensure you always have more than you need.
That's where I come in! Let’s work together to optimize your boat’s electrical energy budget. With a personalized action plan and guidance, you’ll gain confidence in managing your power needs efficiently. Contact Chris squidandjellysgreatadventure@gmail.com
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