How do you get power when sailing ?

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Whilst the sailing world is undoubtedly grateful to companies like Raymarine for the incredible safety and information technologies that we now take as standard when we are at sea, we have to remember that every one of these devices takes power.

The electronic self-steering gear, the chart-plotter, the radar, the radio, and other devices all require power, as well of course, as the traditional powered devices like the refrigerator, the freezer, the lighting systems, the desalinator…

On yachts, this power comes typically from a series of batteries, and generally, there will be two distinct systems. The first is the engine battery, used like a car battery to start the engine and the other is the ‘house’ or ‘hotel’ system, which will be a bank of batteries that will power all the other devices. These will normally be in banks, and the number of batteries and their power depends on the requirements of the particular boat.

Recharging these batteries and providing sufficient power to keep the batteries charged, and consequently healthy for a long voyage, is a subject that the entrants to the Global Solo Challenge (GSC) will be thinking about, as they will be away from any shore power for several months and in vastly different climatic conditions from Ocean to Ocean.

Traditionally, the batteries would be charged by simply running the engine or a diesel generator unit, and then power would be drawn via the alternator to charge both sets of batteries.

Aside from properly installed diesel generators, some smaller boats venture into the use of petrol generators, these however are dangerous both for their exhaust fumes and the dangers involved with carrying cans of petrol, which unlike diesel can explode, and its fumes are highly flammable.

The Global Solo Challenge does not forbid the use of the engine and fossil fuels to produce energy altogether but keeping sustainability and the environment in mind has, for this edition, introduced a cap of 300lt of fuel per boat at the start. Most skippers will use some of this diesel for heating the cabin too in the coldest sections of the event, so, overall, this fuel is insufficient to complete the challenge and satisfy all of the energy needs, especially for the slower boats.

This encourages all the skippers to explore alternative means of producing power (and even heat to warm up).

The first and most obvious way to charge the batteries is via solar power. A solar panel is attached to the surface of the yacht, pointing towards the sun, and hey presto, power is produced. These systems work well, particularly if, like me, your boat is in an area of Spain where we enjoy over 300 days of sunshine every year. Nearly all the entrants to the GSC that I have spoken to will incorporate a solar power system into their yachts.

The biggest problem for the boats taking part in this challenge is, that the majority of their time sailing around the world will see the boats in the Southern Ocean, an area that is known for its almost perpetually dark, grey skies and lack of sunshine. This means that alternative sources of power will be required for this part of the challenge.

One alternative is to install a wind turbine generator, and indeed in the recent past, these units have proved to be popular, however, there are limitations as to how effective these units are, particularly when the yacht is running before the wind. The entrants to the GSC will hope to spend the majority of their time running before the wind, following the prevailing ‘trade’ winds as they travel around the Globe.

I should explain that wind generators work best at higher wind speeds and it is the ‘apparent’ wind speed that counts. The apparent wind speed on a boat is what the skipper will feel. So let’s say we have a 20-knot wind and we are running before it and sailing along nicely at 12 knots, the ‘apparent’ wind speed on board would only be 8 knots. This is the wind speed that would hit the wind turbine, which would probably be insufficient to keep the batteries fully charged.

A more recently introduced alternative is to install one or maybe two hydro generators. These units have a reverse propeller (an impeller), which spins as the yacht sails along. This rotation is applied to an alternator and AC power is produced. This power is then rectified to DC power to charge the batteries.

Early models of these units were literally towed behind the boats, but obviously, there were problems in these getting fouled and indeed some large fish mistook these units as being lures and ate them!

Today’s models are generally small stern mounted and look like a small outboard motor on the transom. Boats will often opt for two of these units. These types of units were first seen in the 2008 edition of the Vendée Globe when they were installed on a number of the competing Imoca 60s.

There is some drag, but this has to be seen against the saving in weight achieved by not having to carry the full weight of diesel. The drag has been calculated at being often no more than ½ knot and of course, when the extra power this unit produces is not required they can be readily lifted out of the water, like an outboard engine.

Using modern effective technology means that on a 40ft yacht, these units can readily produce 200 Ah every 24 hours, whilst sailing at 6 knots, and it is generally assumed that such a yacht, at this speed, will consume between 180 and 240 Ah per day.

The main problem with these units is that they are not particularly efficient when the yacht is being sailed at lower speeds, but hopefully, when there is little wind and therefore less speed, then the yachts will be able to use solar power to maintain their batteries or the skippers may opt to use the engine in such conditions.

At least one entrant to the GSC is investigating a combination Servoprop saildrive system that uses a patented system where the boat has an electric engine for when it is needed but this serves as an efficient hydro generator at other times. This will then be augmented with a solar power system.

Fuel cells running on ethanol are also readily available and a very popular choice on Mini 6.50s. The best-known brand is EFOY, they are expensive but very efficient, quiet, and only produce a dribble of water as waste, of course, the fuel must be carried to use one but this would be less than the diesel needed to run the engine to charge via alternators.

Most GSC entrants that I have spoken to, will be using a combination of at least two of the above systems.

Future technologies that are gradually being introduced include hydrogen fuel cell-based power units, but it will probably be a few more years before these are readily available and generally affordable.