Mike Morgan shares tips on enhancing power management on a yacht to conserve valuable amps for those who appreciate their comforts at sea.
I admit that I’m not a marine electrician, and my knowledge of boat electronics is quite basic. However, after three seasons of overseeing my boat’s power generation and usage, I’ve developed a system that appears effective. I hope you find some of this advice helpful in managing your yacht’s energy requirements.
Each boat presents a unique balance of power generation and usage, meaning my strategy may not fit your needs precisely, but it could be a starting point for more efficient management of your valuable amps.
My wife Debbie and I sail for up to nine months each year around the Mediterranean, primarily anchoring rather than staying in marinas, using our generator sparingly to align with our environmental values and budget considerations.
I won’t cover power needs while sailing here, as it does not align with our cruising habits. Obviously, for an Atlantic crossing, you must account for the power demands of navigation equipment, lighting, and auto-pilots.
We purchased our cherished Spirit, a brand-new Bavaria C57, in 2021 and made several upgrades to work toward the ideal of self-sufficiency at anchor. We chose to install lithium batteries with a capacity of 800 amp hours (Ah), weighing less than a single 150Ah lead-acid battery.
Since lithium batteries offer roughly double the capacity of their lead-acid counterparts, 800Ah equates to 16 lead-acid batteries rated at 100Ah while collectively weighing just over a third of a ton. Thanks to Spirit’s wide beam, we managed to install four 420W solar panels, resulting in a possible maximum output of 1,680W.
A selection of electrical appliances in Mike’s Bavaria C57 kitchen and the wattages that similar items might draw from your battery with an inverter.
Battery State of Charge
The available electrical power revolves around batteries. Boat batteries are typically rated in amp hours (Ah), indicating the total number of amps consumed within one hour of usage. For instance, a 120Ah battery theoretically supplies 120A for one hour or 1A for 120 hours. However, this explanation is somewhat oversimplified.
With lead-acid batteries, it’s crucial never to discharge them completely unless frequent replacements are in your plans. These batteries should not be discharged below 50 percent, meaning the practical Ah available is actually half the theoretical rating. In the example above, you’d reach a limit of 60 hours at 1 amp before needing to recharge. Generally, a battery’s charge level is monitored in volts or via a shunt battery meter.
Understanding your battery charge state is essential for managing power requirements.
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I swapped out the standard 240Ah domestic lead-acid batteries in our Bavaria for 800Ah of lithium batteries. The benefit of lithium lies in its lower weight. Unlike lead-acid options, lithium batteries can be discharged to much lower levels, though a downside is their potential to explode.
To mitigate this risk, they require a battery management system, ideally installed by an expert who understands the nuances of marine electrical systems.
Oceanvolt lithium batteries installed on a Feeling 32.
Charging Sources
A typical production boat comes equipped with a 60A charger used with the generator, if available, or when plugged into shore power. The engine features an alternator that usually produces between 35 and 60A of charge, depending on its size.
With a 60A supply, batteries can receive 60A in one hour. For instance, having 800Ah of lithium batteries and starting from 50 percent would require about 6.6 hours to fully recharge (400 amps divided by a 60 amp charging source equals 6.6 hours).
However, the process is more intricate involving various charging states—bulk, absorption, and trickle (maintenance or float)—along with battery types that have different ratings, which I’ve simplified here for clarity.
If shore power isn’t available (as at anchor), or if you lack a generator, you can run your engine for six hours under light load, a scenario that’s not ideal for the engine nor for nearby boaters hoping for a tranquil sunset.
Mike’s custom electrical control panel.
Battery Charger
Increasing your battery charger’s size will hasten charging times from both the generator and shore power. I opted for a 120A charger along with a 3kW inverter for my 240V appliances. Alternatively, you can upgrade the engine’s alternator to better sustain a power-hungry bank of batteries, but again, this necessitates prolonged engine operation.
The 9kW Paguro 9000 generator I installed offers much more power than we generally require. It serves to power both the 240V ‘ring main’ and the battery charger. Nonetheless, battery charging is constrained by the charger’s power rating—in my case, 120A.
Four solar panels mounted on Spirit’s stern arch, generating a maximum of 1,600W.
Renewable Energy
When it comes to renewable energy for boats, options include wind, hydro, and solar. I selected solar with a tailored stern arch featuring four 400W panels that yield a theoretical maximum output of 1,600W at 12V—equivalent to 133A.
Just like lithium batteries, solar panel output and voltage must be managed. Each panel features an MPPT (maximum power point tracking) controller to ensure correct voltage and current levels reach the batteries when sunlight is plentiful. The next hurdle is maintaining a balanced power consumption relative to the boat’s usage.
The stern arch was purpose-built to accommodate the solar panels.
Background Noise
I began by creating a spreadsheet to track the power ratings of my various onboard electrical devices. This proved challenging as it involves calculating each appliance’s power demands, estimating runtime, and scheduling usage.
This required mapping out a theoretical power demand across time to gauge how much power to generate. Estimating solar panel output alone felt daunting, involving assumptions related to sunlight hours, sun angle, panel efficiency, and even planning for solar eclipses! Ultimately, I decided to adopt a more realistic strategy.
I first measured our boat’s ‘background noise,’ meaning the power being consumed while anchored with no significant appliances in use.
It averaged around 200A, which is rather high; however, I operate three fridges and a deep freezer alongside ample internal lighting—akin to Blackpool Illuminations!
The duration to recharge my batteries varies significantly based on the boat’s orientation. If the stern faces direct sunlight, my batteries recharge fully in a few hours; conversely, with the bow facing the sun, the process takes considerably longer.
On a typical day, we achieve 100 percent by midday or early afternoon, allowing an additional four or five hours of surplus energy for pressing systems.
Air conditioning is a heavy drain on battery power.
Power Consumption
Our yacht is equipped with numerous power-hungry devices such as a kettle, coffee maker, hair dryer, and microwave; however, I disregard these for power management due to their sporadic and brief usage.
Conversely, we have several critical appliances, including a washing machine, water maker, ice maker, and water heater, which demand high power and can operate for extended periods. My air conditioning system can run off the inverter, but I prefer using fans and keeping hatches open for comfort while anchored. When possible, I reserve air conditioning for when shore power is accessible or the generator is operational.
Our Bavaria features an integrated utility room which allowed us to install a full-sized washer-dryer, a favorite upgrade of ours.
To manage this equipment, I maintain a rota assigning specific days for either water production, laundry, ice making, or heating water. We do laundry weekly without utilizing the dryer, opting instead for nature’s dryer outside, which can occasionally detract from the aesthetics of a serene anchorage.
The water maker generates 60 liters per hour, usually running for about four hours to sustain us for several days. I position ice-making and water heating for other times.
Hosting guests who prefer showering after swimming necessitates running the water maker nearly every day. In these situations, I often struggle with energy balance and may need to resort to generating power.
We selected a Schenker Smart water maker that produces 60 liters per hour, rated at 20A, allowing continuous freshwater production thanks to our solar array.
I usually delay running the generator until battery levels drop to around 30 percent in the morning. At that point, I operate the generator for three to four hours, bringing my batteries back up to approximately 70-80 percent, allowing the solar panels to resume charging.
When the generator is on, I capitalize on extra power by running as many devices as possible: I produce water, run the air conditioning, and heat water. Utilizing every precious amp is critical! On average, I operate the generator every eight to ten days when it’s just us and every four to five days with guests.
Batteries can be conveniently dispersed throughout a yacht.
Improving Power Management on a Yacht
Before expanding your service battery bank’s capacity, calculate your total power requirements by multiplying the amperage of all devices by the time they will run over a charge cycle (usually 24 hours).
Sum the amp hours, double that figure (to prevent going below 50 percent charge capacity), and then add another 20 percent as a safety buffer.
If separate engine start and service batteries exist, but you want to add more service batteries, ensure they’re of the same age, type, and capacity (Ah rating) as the existing ones. For optimal results, it’s better to construct your service bank from several smaller batteries linked together to obtain the necessary voltage and capacity.
For a large bank of batteries (500Ah or more), it’s often advisable to use 6V batteries since they facilitate the creation of a significant deep-cycle bank while remaining portable and able to be distributed across a broader space.
Enhance your service bank by connecting multiple smaller batteries.
Charge Maintenance
Upon selecting the battery type, ensure sufficient charging power is available to fully charge them between cycles. As a general guideline, aim to bulk charge at a minimum of 10 percent of the battery bank’s rated capacity (e.g., 20A for a 200Ah battery).
However, targeting 20 percent is preferable if you wish to fully recharge within one night at a marina. Modern AGM (absorbent glass mat) batteries generally accept more charge than traditional wet lead-acid types, although gel cells require a careful charging regimen to avoid damage.
Chargers (both shore and alternator type regulators) should feature multi-stage systems including bulk, absorb, and float phases. This method allows batteries to be charged rapidly to about 90 percent before the voltage declines, facilitating the final charging phase more gradually and preventing overheating and gassing.
A smart battery monitor lets you observe your state of charge and remaining capacity.
Temperature has a significant impact on a battery’s ability to discharge and charge. The colder the battery, the more power it requires to achieve a full charge. Thus, always utilize a charger or regulator equipped with a temperature sensor for automatic adjustments based on differing conditions.
Most power devices provide a trickle charge, mainly maintaining the engine battery voltage. However, if you intend to install a robust (5A+) wind generator or large solar setup, a voltage regulator is essential to prevent overcharging. This can range from a small solid-state switch suitable for minor solar panels to a substantial dump resistor that dissipates surplus charge in a wind generator by heating a wire-wound resistor.
Battery Monitoring
The most straightforward method to keep your batteries in excellent condition is daily observation of their state of charge while aboard, using a modern ‘smart’ battery monitor. It offers real-time feedback on current flow, charge status (SOC), and remaining capacity. Many of these devices include alarms for low voltage or warn of excessive charging.
A rough SOC estimate can be obtained from a voltmeter; however, this is not highly reliable and can yield inaccurate results when a battery is recently charged or under significant load. It’s advisable to install a monitor equipped with a shunt, measuring current flow over time to calculate remaining charge capacity far more accurately.
Hydrogenerators like this Remoran Wave 3 effectively recharge a yacht’s batteries while underway.
Optimizing Solar Energy
Solar panel efficiency can suffer from saltwater exposure and the cumulative effects of UV radiation and high temperatures. Regular maintenance is key to ensuring optimal solar performance.
Clean your solar panels in the early morning when they are coolest, as doing so while warm or in direct sunlight can induce thermal stress. Utilize distilled or deionized water to prevent mineral deposits on the panels, steering clear of harsh chemicals or abrasive cleaners that could scratch the photovoltaic surfaces. Allow panels to air-dry or gently wipe with soft cloths, leaving no moisture on the surface. Periodically check for cracks, breaks, or loose connections.
Hydrogenerators
Hydrogeneration has seen considerable efficiency improvements in recent years. The concept is straightforward: the boat’s movement through water turns an alternator mounted on a transom-based hydrogenerator, generating electricity to top up the batteries. With speeds of 7-8 knots, generating 300Ah per day is a reasonable target.
Oceanvolt’s High Power ServoProp 25 electric saildrive.
Main Propeller Regeneration
It’s also possible to utilize the main propeller for ‘regenerating’ electricity while sailing by employing a parallel hybrid propulsion system that integrates an electric motor alongside the existing engine. Systems supplied by Lynch Motors in Devon have been used for years in Vendée Globe boats as regenerators, with a newer Red Snapper electric motor designed for cruising yachts.
However, the pitch needed for the propeller to effectively push the boat through the water may not always align with that required for optimal regeneration. Manufacturers have developed various solutions to this issue.
Oceanvolt’s ServoProp designed for saildrives can electronically adjust its pitch according to speed and function. The latest model boasts full 360-degree blade movement, optimizing efficiency; for instance, at a speed of six knots, it can produce an impressive 1kW of power.
Bruntons has introduced the innovative Autoprop, which automatically adjusts its pitch to match the vessel’s speed. The Ecostar variation of this prop generates 200W at five knots and can create up to 1kW at 10 knots with an electric motor.
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