Optimizing Alternative Energy

Vessel size and electrical load will influence solar, wind and water systems

A successful ocean voyage depends largely on the way we manage energy on our vessels, be it from the wind, the sun, the ocean, the auxiliary engine or a separate generator. As offshore sailors, our goal is to gain not just maximum output from our energy sources, but the optimal mix in order to save fuel, money and time lost to repairs.

Getting optimum performance from your vessel’s array of energy sources requires us to first of all select those systems best suited to our personal needs and those of the vessel. A small boat can often get by with a minimal array of electrical equipment and battery-charging sources, while a larger yacht with a front-opening refrigerator, deep freeze, air conditioning and separate antenna domes for worldwide television and telephone service naturally will need a large, robust power-generating system completely independent of the main power plant.

Before committing your financial resources to a long list of charging equipment, first calculate how many amp hours your boat is likely to use in a 24-hour period while offshore and while at anchor. Do not assume you will have the same needs at anchor as you will while underway.

At sea, your charge power will need to keep up with navigation systems, most of which, if not all, will not be deployed in an anchorage. While at anchor, you will continue to use, as a minimum, the cabin lights, the masthead light, a VHF radio, an SSB radio and perhaps a fridge. What you will not need are the depth sounder and other navigation systems, although some skippers keep these systems up and running 24-7 at anchor, as if they were underway. The difference in power usage really depends on your needs and personal preferences.

To give you an idea of how to optimize alternative energy systems on cruising boats, the simplest way is to organize your options according to boat size. Obviously, there are endless possible exceptions to what you will read here. You may visit a 60-foot ketch with little more than a simple GPS and paper charts for navigation, while the 30-foot sloop next to her will have a sophisticated chartplotter, radar, hot and cold running water, and a fridge. However, these tend to be exceptions to the rule.

At the risk of oversimplifying the manner in which sailing vessels are typically equipped in terms of alternative energy-generating arrays, we can divide cruising vessels into three groups: pocket cruisers (25 to 34 feet LOA), midsize vessels (35 to 44 feet LOA) and larger vessels (45 feet LOA and up).

Pocket cruisers
At the humbler end of the offshore sailing spectrum, pocket cruisers typically have rather meager power needs. With a standard, non-charting GPS and a traditional, stand-alone depth sounder used only for anchoring, plus navigation lights, the most power this vessel is going to use at one time will be only a few amps. And since the engine will be running during anchoring, the typical 55-amp alternator will be producing more than the required amount of current to support all these functions simultaneously.

While on passage offshore, some small-boat cruisers eschew the depth sounder and chartplotter, checking their position every few hours under the glow of a single cabin light and marking GPS coordinates on a paper chart with triangle, dividers and pencil.

For communication, even on the smallest ocean-going sailing craft, a VHF radio and a ham or marine SSB radio are standard equipment. Today’s VHF should include AIS and GPS capability, even if it is not connected to a chartplotter. The small screen on the Standard Horizon GX2400 VHF radio with AIS and GPS capability gives you a rough visual display of vessels in your area, along with call sign and ship name. You may adjust the scope of the area coverage with the handheld control pad. In standby mode, the GX2400 consumes only 0.45 amps on standby, which your humble power-generating system can cover easily.

Given these meager systems in cruising mode, your small vessel can be expected to use roughly 15 to 20 amp hours per day, which is easily covered by a 55-watt semi-flexible, monocrystalline SunPower solar panel. At a rated daily output of 23.6 amp hours per day, this panel, measuring only 21 x 23 inches, will keep up with your needs reliably as long as the sun is shining. SunPower’s line of rigid panels are larger and produce much higher levels of charging power.

Even at 55 watts, a solar panel can burn out a house battery if charging is not carefully controlled. An inexpensive 130W/8A solar charge controller from Nature Power will protect your battery banks for the princely sum of 20 bucks. Or, for slightly more, you can pick up a Sunsei 10A Solar Charge Controller, which has served flawlessly on my 1966 Cal 30 Saltaire for more than a decade. With both systems, you simply connect the solar panel wires to the unit, and then two wires from the controller to the house bank and forget about it. That’s a lot of protection for such a minimal cost.

As for self-steering, smaller vessels tend to rely heavily on windvane systems, particularly servo-pendulum systems because they connect directly to the tiller or wheel steering. These machines keep boats on track by correcting course variations via a vertical windvane connected to a submerged servo blade, which in turn corrects the helm with steering lines. Some of the more popular models include the Fleming Global Windvane Self-Steering System, the Sailomat, the Aries and Scanmar International’s Monitor.

The main goal for pocket cruiser skippers is to keep systems simple yet effective at minimal cost. They go to all the places the big boats go, but with a greater dose of adventure at a fraction of the cost.

Midsize cruisers
The majority of cruising boats, those in the middle range of roughly 35 to 44 feet, generally have skippers who expect more from their boats than simply an icebox, running lights, a couple of radios, and a GPS. Typical among these boats are a radar dome, a top-loading fridge, a chartplotter coupled with a VHF/GPS/AIS radio and of course, an SSB or ham radio transceiver.

Also ubiquitous aboard today’s midsize cruisers is an array of personal electronics and entertainment systems, including a laptop computer, perhaps a bulkhead-mounted flat screen for watching movies, a video game system, a stereo with a pair of powerful speakers and a charging station for cell phones. And if you have an ice maker onboard, don’t forget the blender for making margaritas!    

These midsized vessels will keep up with their charging needs with a large solar panel array, a wind generator and perhaps a hydro generator as well. Unlike the older hydro generators, which featured a turbine towed by a long piece of double-braided line, the latest iterations of these chargers are mounted to the rear deck or transom. A hydro generator affixed to the vessel eliminates the hassle of hauling in a spinning piece of line, plus the possibility of losing the rig to a hungry shark.

The Watt & Sea hydro generator, built in La Rochelle, France, and distributed by Hydrovane in British Colombia, is comprised of a long, thin NACA foil strut with a rotor at the base, which is deployed by manually lowering it straight down into the water. The unit may be deployed and retrieved while the vessel is underway.

The cruising version of the Watt & Sea produces roughly 300 watts of power, depending on hull speed, so with only four hours of operation, the battery banks receive 1,200 watt hours, or 100 amp hours, of charging. The only drawback, of course, is this device can be used only while underway offshore, away from coastal areas that might be home to kelp beds. While the vessel’s prop is protected by the vessel’s keel or skeg, the Watt & Sea’s prop appears to have little protection from the shaft housing at the leading edge of the foil.

Whereas water generators are used while under sail, a wind generator finds its true place at anchor, taking advantage of breezes from the ocean and from ravines in coastal hills. To appreciate the power of a wind generator, we need to understand the basic physics behind this apparatus.

If you have ever watched a pinwheel in a slight breeze, you have noticed the blades spin at erratic speeds, barely revolving in a mild zephyr and then racing quickly in a slight gust. This is because the power available from the wind increases as the cube of wind speed. So when the average wind speed doubles, power is multiplied eight times. For example, a five-knot breeze will produce 125 units of power; at 10 knots, the power available zooms up to 1,000 units.

However, no matter how efficient a wind turbine’s blade may be, according to Betz’ Law, the maximum amount of kinetic energy that may be drawn from the wind is less than 59 percent of the wind’s total power. Despite these limitations, which are endemic in all wind generators and airplane propellers, the overall power produced by marine wind generators can keep your battery banks topped off at anchor with virtually no tending or maintenance.

Before investing in a wind generator, study the various makes and models before committing your money and time to a particular unit. First determine what your amperage needs will likely be while at anchor, what your battery capacity will be and how much space you can devote to a mounting structure. Although the unit may come with a mounting mast, you will need to add extra diagonal supports to ensure a storm-proof installation. 

One very popular wind generator is the Primus Windpower Air-X Marine Wind Turbine, which is a brushless, permanent magnet alternator capable of producing up to a kilowatt of power per day. This is obviously far more than the typical, small, cruising sailboat can expect to use. At a modest 10 knots of apparent wind speed, the Air-X cranks out 12 amps, or 288 amp hours per day, a whopping amount of power, more than enough for a fridge and a full complement of onboard electronics.

Invariably, the majority of cruisers use their wind generators 24 hours per day in anything less than a full gale, at anchor and at sea. This is fine if you are sailing to weather in a force 5 wind, but in a light, downwind, 10-knot breeze with a hull speed of four knots, the air speed across the rotor is only six knots, producing very little amperage. Hence the need for a water generator, which produces a substantial level of current even at a moderate hull speed.

For self-steering, boats in this middle size range generally depend on windvane self-steering, but many of their skippers opt instead for an electronic autopilot, or a combination of both systems. Much of this decision is based on weighing electrical power drawn from alternative energy versus the practicality of windvane steering, given the rear deck layout and potential blocks to wind current needed for steering action.

Large vessels
Vessels from roughly 45 to 50 feet LOA and up tend to make less use of alternative energy sources than their smaller kin, but there are still plenty of energy-saving systems that can make the larger yacht more affordable to maintain and operate on a long cruise.

Whereas a midsize yacht is commonly equipped with solar panels, a wind generator, and a water generator, many larger yachts tend to depend heavily on a diesel generator to keep up with pressurized water, a water heater, radar, television and/or telephone antenna domes, a large refrigerator and deep freeze, bottom-mapping sonar and perhaps even air conditioning. 

With all these systems running around the clock, a dependable genset, such as one manufactured by Northern Lights, Kohler, Fischer Panda, Mastervolt, Beta Marine or others, can meet the need for a steady flow of current to the house battery bank and the entire onboard power grid.

At the humbler end of the genset range is the Next Generation UCMI-3.5, which generates 3.5 kW of power at 2,800 RPM. This model consumes roughly a liter of fuel per hour, weighs 160 pounds, has a footprint of 30 by 18 inches and is only 16.5 inches tall. The UCMI-3.5 is powered by a single-cylinder Kubota diesel engine, which is known for its longevity and easy maintenance.

Toward the upper end of the scale is the Northern Lights genset, which produces six kW at 1800 RPM and consumes 1.1 to 2.2 liters of fuel per hour, depending on conditions. This unit is powered by a three-cylinder Lugger diesel engine, weighs 365 pounds and measures 28.5 by 20 by 20.4 inches. The Northern Lights six kW genset was obviously designed for the large yacht aboard which a belowdecks autopilot, plus a full range of navigation electronics, communications systems and lifestyle amenities, are regarded as absolute necessities.

The charge controller used on the larger yacht is far more complex than the little Sunsei on Saltaire. Rather than a simple controller, larger vessels may opt for a combination charge controller and DC-AC inverter, such as the Mastervolt CombiMaster 12/2000-100 inverter-charger, which protects batteries while providing full-sinewave, 120-volt AC current, just like the electrical power you enjoy onshore.    

Another key component in an energy-conscious, onboard electrical system is a robust set of battery banks designed specifically for offshore cruising. Today’s cruising sailor can choose from an assortment of batteries in various combinations of sizes to meet their boats’ electrical storage needs and installation size limitations.

In addition to the starter bank, which must align with the engine’s requirements, the cruising skipper may select from a wide selection of sizes and types of house batteries. Traditional big-yacht cruisers often still prefer the durability and flexibility of two or more flooded 8D banks. These time-tested, rough-and-tumble batteries can withstand variations in charge voltage with little or no damage to the cells.

A top-of-the-line flooded cranking battery has higher cold cranking amps than any other type of battery with roughly the same reserve minutes. If there is one drawback with flooded batteries, it is the corrosive acid bath, which can cause severe damage to the vessel and crew in the event of rupture. However, in all my years of offshore and coastal cruising, I have never experienced, nor heard of any other skipper contending with, a ruptured flooded battery. Batteries are fitted tightly into their compartments below the waterline where they do their jobs silently and effectively for many years.

Absorbed glass mat (AGM) and gel batteries have gained ascendancy in cruising circles over the last 20 years, mainly because of their ability to shrug off wild fluctuations in charge levels. AGM banks charge up faster than flooded banks, and they are less prone to harmful leakage in the event of rupture.

A key characteristic of silica gel batteries is their ability to sit completely uncharged for up to a month yet still accept a full charge. They are also resistant to overcharging and keep a full charge much longer than a flooded bank. If you are headed for colder regions, you will appreciate the gel battery’s ability to function in extreme cold without freezing. On the downside, these cold-loving batteries suffer from their intolerance of excessive heat. Any gel battery installation should be away from the engine compartment in order to prevent an early death to this bank.

When it comes to self-steering options, the majority of large vessels depend on an electronic autopilot to tend the helm. And it is easy to appreciate the logic in this option. Today’s autopilots can be integrated into the vessel’s GPS chartplotter along with feedback from a mast-top-mounted wind sensor to fine-tune directional control for optimum sailing angle.

This latest evolution in autopilots helps to save money on fuel while reducing wear and tear on the power plant and gearbox. The pairing of directional control with wind sensing also adds to the pure pleasure of sailing, which is why we’re out on the ocean in the first place.      

The B&G H5000 autopilot, designed for larger yachts, is a favorite among cruisers and offshore racers alike. This system is comprised of five essential components: the NAC-3 Autopilot Computer, the RF25 rudder angle sensor, the Precision 9 compass, your choice of H5000 CPU and a pilot computer.

And lest you thought windvane self-steering was the exclusive domain of smaller cruising boats, there are at least two vane gear models designed specifically with the larger yacht in mind. The Saye’s Rig, available from Scanmar, is unique in that it operates as both a servo-pendulum and a trim tab unit, connected directly to the vessel’s main rudder by a long, U-shaped stainless pipe.

A particularly interesting feature of the Saye’s Rig is the vertical-axis, wedge-shaped canvas air vane, which enables broader, more stable wind-sensing range. This device was designed for vessels in the 50- to 65-foot range and may be used with any type of main steering, including hydraulic steering.

Another option is the ubiquitous Hydrovane, by far the most frequently seen vane gear on yachts roughly 40 feet to 50 feet in length around the world. The Hydrovane owes its popularity to its simple design, easy installation and intuitive operation. Unlike a servo-pendulum gear, the Hydrovane incorporates a long air vane, which converts changes in wind direction into steering action through an auxiliary rudder. The operator sets the manual control to one of three settings, then inclines the air vane to compensate for prevailing wind speed, thereby modifying the vane’s leverage on the rudder.

A great added benefit of the Hydrovane is its capacity to replace the main rudder in case of failure. Even in a flat calm, the vessel may be steered manually by simply dipping the air vane to either side for course correction.

Every type and size of sailing craft lends itself to an array of potential alternative energy systems. It is up to you as the skipper to decide how to make optimal use of the systems available for your yacht. Whether you are cruising in familiar coastal waters or crossing oceans, your voyages under sail will leave a smaller footprint on the natural oceanic environment and save you money at the same time. n

Circumnavigator-author Bill Morris believes the best strategy for succeeding as an offshore voyager is to keep systems simple and, if possible, manual. Key to survival are a windvane self-steering system, a basic array of electronics and an aggressive alternative energy battery charging matrix. Bill is a frequent contributor to Ocean Navigator and the author of The Windvane Self-Steering Handbook (International Marine, 2004); Sun, Wind, & Water: The Essential Guide to the Energy-Efficient Cruising Boat (Seaworthy Publications, 2017), and The Captain’s Guide to Alternative Energy Afloat (Seaworthy Publications, 2019).

Categories: Marine Technology, Ocean Voyaging, Offshore Sailing