Sailboat Wind Generators and
Water Turbines

There's no doubt that a sailboat wind generator will make a significant contribution to the amps on call-up duty in your battery bank. And the more wind - up to a point - the greater will be the contribution.

A wind generator, wind turbine or wind charger as they're also known, senses only the apparent wind rather than the true wind, which is why they are much more effective on some points of sail than others.

On a typical tradewind Atlantic crossing for example, with the wind astern, their performance is likely to be disappointing. With say a 15 knot following wind and a boat speed of 6 knot, the resulting 9 knots blowing through the blades, your sailboat wind charger won't be earning its keep.

But having made your Caribbean landfall and cruising in the West Indies, it will be a different matter. Now beam winds and breezy anchorages will ensure that your sailboat wind generator provides generous and consistent battery charging.

Types of Sailboat Wind Generator

The power produced is generated by spinning a DC generator or—more commonly— a 3-phase AC alternator, with an internal rectifier to convert AC to DC. There are three horizontal-axis types, defined by their blade configuration:

2-bladed;
5-bladed;
3-bladed.

The 2-Bladed Type:

More accurately, these are a single blade as seen in the pic. They use a generator to produce power, unlike the 3 and 5-bladed types that use an alternator.

These types perform better at lower wind speeds - the quaintly named 'WindBugger' or the Hamilton Ferris (shown here) being good examples of the breed.

They tend to produce a low frequency 'whump whump', while the higher speed 3 and 5 bladed types can produce a penetrating howl that even a teenager wouldn't appreciate.

The 3-Bladed vs the 5-bladed types

The choice between 3-bladed and 5-bladed turbines can be perplexing, unless you understand their distinct characteristics. They're not cheap so you need to get this right before you splash out on one.

The most fundamental difference lies in their performance relative to wind speeds.

3-Bladed Marine Wind Generators

3-bladed turbines, often seen as the workhorses of wind power, are designed to excel in higher wind conditions.

Their aerodynamic design allows for a higher tip speed, translating to increased power generation when the wind picks up. This makes them particularly suitable for cruisers who frequently navigate areas known for strong, consistent winds. Moreover, their lower drag and starting torque mean they can begin generating power even in relatively light breezes, a significant advantage when trying to maximize energy capture.

However, the efficiency of 3-bladed turbines in strong winds comes with a trade-off: noise. The higher tip speed inherently produces more noise, which can be a significant consideration for those seeking a tranquil onboard experience, especially during overnight stays.

5-bladed Marine Wind Generators

Conversely, 5-bladed turbines are engineered to thrive in lower wind speeds.

Their design focuses on maximizing energy capture from gentle breezes, making them ideal for areas with lower average wind speeds. The increased number of blades provides a greater surface area for interacting with the wind, resulting in a higher starting torque. This means they require a bit more wind to initiate rotation, but once spinning, they efficiently convert light winds into usable energy.

A key advantage of 5-bladed turbines is their quieter operation. The lower tip speed significantly reduces noise levels, contributing to a more peaceful onboard environment. This makes them a preferred choice for sailors prioritizing comfort and minimizing noise pollution.

Selecting the right wind turbine for you..

When selecting a wind turbine for a sailboat, several factors come into play. Wind speed variability is paramount. Sailboats often encounter a wide range of wind conditions, from light zephyrs to gale-force gusts.

If your sailing grounds are characterized by consistently strong winds, a 3-bladed turbine might be the more efficient choice. However, if you frequently sail in areas with lighter, more variable winds, a 5-bladed turbine could prove more effective.

Noise is another critical consideration, especially for extended voyages. The tranquility of a quiet anchorage can be easily disrupted by a noisy turbine. 5-bladed turbines generally offer a quieter operation, less likely to upset your neighbours.

Furthermore, starting torque plays a role in energy capture. A lower starting torque, as found in 3-bladed turbines, allows for energy generation in lighter winds, which are common in many sailing environments. Conversely, a higher starting torque, as in 5-bladed turbines, requires more wind to initiate rotation.

Ultimately, both 3-bladed and 5-bladed turbines can effectively charge 12V batteries on sailboats. The optimal choice depends on the specific wind conditions encountered, the sailor's priorities regarding noise, and the desired power output. By carefully evaluating these factors, sailors can select a wind turbine that best suits their needs and maximises their onboard energy independence.

Manufacturers of the high speed, high efficiency types of sailboat wind generators are at last getting to grips with the noise problem through combining sophisticated blade design with high tech lightweight materials.

And your sailboat wind generator will be more effective in some parts of the world than others. In the Mediterranean for example, where calm conditions are frequent, other forms of green power such as solar panels may be a better option.

The Drawbacks of Wind Turbine Generators on Sailboats...

Towed Water Turbine Generators

The components of a towed generator, (aka water turbine) are an impellor, 20m to 30m of rotating towline coupled to a pulpit-mounted generator from which a cable delivers the charge to the batteries. Towed generators typically produce around 5A at 6 knots.

They really score over their wind driven brethren in light wind conditions or on long downwind passages where a sailboat wind generator would be seriously impaired by the lack of relative wind. In such situations a towed generator will continue to churn out the amps.

Towed water turbines have a keen following in many long-distance blue water sailors, but they do have their own problems:

Drag. They will typically take between a third and half a knot off your speed;

At speeds much above 7 knots they tend to skip along the surface, generating nothing but disappointment. This can be compensated to a degree by adding sinker weights to the impellor, and/or using a longer than standard towline. Some manufacturers offer an alternative coarser pitched unit which is good for speeds up to 12 knots, but at 6 knots this version will only be generating around half of what the standard unit would;

In heavy seas they can leap out of the water, where the spinning tow rope is likely to snarl up into some impressive kinks and twists;

Sharks have been known to consider the impellor as part of their diet.

You should forget about trolling a fishing line when you're towing one of these. The resulting tangle has to be seen to be believed.

Combined Wind/Water Turbine Generators

Towed generators are not much use at anchor, but some manufacturers have overcome this limitation by making them convertible from water to wind mode and vice-versa. The Aquair 100 water/wind turbine is a typical, much favoured example of one of these.

Just occasionally in the marine industry, someone comes up with a really neat idea. This time it was Eclectic Energy Limited, the manufacturers of the innovative DuoGen Combined Water/Wind Generator.

Unlike a towed unit this is a one piece design, which is permanently attached to the transom. Swing it down into your stern wave where it will act as a water turbine; swing it up and you've got a wind charger.