Propelling to fossil freedom – simple and cheap

Hydro generation covers an essential part of a sailor’s energy need, next to solar panels and wind generation. This third way of supplying stabilizes your energy household. It is like sitting on a tripod instead of a chair with only two legs. When you are sailing and meanwhile the propeller generates electricity, you feel that unexplainable fossil freedom.

Ya sailing: fossil freedom

Hydro energy is free energy, who does not want that? I tell you: too many sailors. 

Hydro energy is safer than a windmill (mostly set too low, so dangerous blades), than a solar panel (can blow away in a storm). Of course, it is also safer than a fossil fuel generator (fire, unhealthy).  Who does not want that? Again: too many sailors. 

Every cruiser, especially the long-distance cruiser, can get the energy really simple, and for low costs. You just connect an alternator to your propeller and you let it run when you sail. We will explain how.

To start with the result: there will be an alternator in your engine room, driven by a V-belt, which runs over a pully around the propeller shaft. When the propeller runs, it will make the alternator run, generating electricity, and a (built in) rectifier will give the voltage your battery needs (most yachts have 12 Volt).

Hydro generation is here to see: a pulley around the shaft (right arrow), a V-belt, and an alternator (left arrow) delivering electricity to your electricity system when the shaft runs.

Balancing RPM, (1) the alternator

The alternator is the most critical thing, so we start here. Most car alternators will start to generate electricity when making 800 rotations per minute (RPM). This so-called cut-in RPM, just tells you it would deliver its first Watt. We want more Watts; practice is to start from 1000 RPM.

If you buy an alternator, check some things:

  • The rectifier. For most yacht systems it must be 12 Volt. Then it delivers till 14,5 Volt to load your battery completely.
  • How heavy the alternator is. If it charges over 80 Amperes at 12 Volt, then make sure it has a double pulley (and double V-belt)
  • Check the diameter of the pulley. It should be rather small; about 50 mm.

Now we go to the next step: how many rotations does the propeller make? Then we can we determine the final step: how many times bigger must the pulley on the propeller shaft be, to get that 1000 RPM? 

Balancing RPM (2) the propeller

A propeller will start delivering a constant strong rotation when the boat sails over 4,5 knots. We take some extra and make it 5 knots. (If you are interested in the theory, Betz’s law tells you all about how much speed is needed to make a propeller run, in water, in wind, whatever)

Now comes the fun part. 

There are two ways to learn the RPM of your propeller: by measuring it, or by calculation. Best is to try both methods.

First the measuring method. 

You set sail and measure the RPMs when you sail e.g. 5 knots. You can buy an expensive RPM meter of 50 Euros or you measure it as follows:

  • take a 20 cm line. 
  • Tape 5 cm of it on your shaft in the engine room
  • When your shaft makes rotations, the end of the line will hit the hull skin: TICK
  • Take the Dictaphone on your mobile phone
  • When your yacht makes 5 knots, push the recording button
  • After exactly 1 minute, you stop recording. 
  • Play the Dictaphone and you see a spike every moment the end of the line makes the TICK
  • Count the number of spikes and you have the RPM of your propeller when sailing 5 knots.

Now the calculation method. 

The number of rotations depends on the pitch of your propeller. You can read that on the propeller. This says for example: 14” X 16”. The first number: 14” stands for the rotation diameter of 14 inch. The 16” is the pitch. This 16-inch (or 0,4 meter) pitch means, that it will theoretically go 16 inches (0,4 m) forward in one complete rotation. 

Suppose you make 5 knots. 

5 knots is 5 X 1852 m = 9260 meter per hour. This is 9260/60=154,3 meter per minute. 

So, your prop would make 154//0,4 = 385 rotations in a minute. So, it’s RPM would be 385. 

But… water is not wood where a screw exactly follows its pitch. Water is ‘’thin’, ‘flexible’. When a propeller delivers propulsion, it pushes a boat forward, but also it pushes water to aft. It ‘slips’. An optimal propeller has 50% slip. 

This makes the propeller’s RPM 385 *2/3 = 257 RPM. 

Believe it or not, if you now check it with the measuring method, you see your results get pretty close to each other. If you measure less RPMs, you have more slip and so perhaps too much resistance. This can be a rough propeller, or friction in the reduction box or the bearing. If you have measured more RPMs, then this is great for your hydro generation, but you could have the disadvantage that the propeller doesn’t work well when you give much RPMs for propulsion.

To the right pulley size

OK, we have now:

  • An alternator that must run 1000 RPM with a speed of 5 knots. 
  • A propeller making about 250 RPM at a speed of 5 knots. 

So, the pulley of the propeller must be 4 times larger. Given the pulley diameter of an alternator of 50 mm, it means that the pulley on the propeller shaft must be 20 cm. 

Most boats have that desired 10 centimetres under the prop shaft, but first check it before you start building. If not, there are alternator pulleys smaller than 50 mm. That saves you triple on the prop shaft pulley.

Next week we focus on efficiency and a more sophisticated system. 

A bridge too close

There is a plan to build a bridge over the river Guadiana, to connect Alcoutim, on the Portuguese side, and Sanlucar de Guadiana on the Spanish side. We wonder if the bridge is a good idea. Because we adore the undisturbed beauty and silence of this place. Will it help these little towns? We are concerned that this bridge will not bring them the desired economic development. Then it would just be a waste of money, spoiling all that makes this place special.

The Spanish Sanlucar de Guadiana seen from Alcoutim…..
and Alcoutim in Portugal seen from San Lucar Guadiana.

The silent call of the Guadiana

A strong flood takes the sailing ship from the mouth of the river Guadiana, under the bridge near the cities Vila Real and Ayamonte, about 15 miles all the way up to Alcoutim and Sanlucar.  

A sailor arrives here when the flood stream starts slowing down to a nice flow. You feel the calm, the peace here. Time to anchor. Easy, because the Guadiana has plenty good anchor grounds. 

The village of Alcoutim has about 1000 inhabitants, Sanlucar about 400. Both places are located ‘at the end of the country’. Or even at the end of Europe. Well, at least it feels that way. Our Portuguese friends all see Alcoutim as the ultimate place of peace and silence in Portugal. They come here, over the little roads, and for them this area is the place to be. The Portuguese and Spanish tourists come to these far ends to enjoy the silence, the handful of friendly restaurants and bars and the idea to retreat in case you need a real still, buzz free holiday at end of the world.

You can kayak, swim, make a small river cruise. If you want to go to the town on other side of the river, you ask the man of the ferry boat to take you there. 

There is also a cable from the one to the other side. Great for hikers. The Portuguese and Spanish walks are fabulous all year round, not in the least because of the undisturbed landscape and silence.

You can walk several beautiful trails here, all equally quiet. Lovely, even when it’s raining.

Our “Ya” is staying here in winter. For decades, there has been a small sailors population of some 50 sailing boats depending on these villages for their services. Each village has a small dockside, which guarantees an international ambience. 

We like our walks here. The area around Alcoutim and Sanlucar is quiet. As long as we’ve been here, the silence is broken only by the occasional motorboat, a single car passing by, roosters crowing, birds singing, a barking dog and people talking. When the sun shines sometimes there’s music from people playing instruments, alone or together. 

A bridge? 

Once every three year there is a bridge during the Festival do Contrabando  (Smuggler’s Festival). Small scale theatres, arts and artisans on both sides and a temporary bridge connecting the villages. This attracts lots of tourists. 

There is a temporary bridge during the Festival of the Smuggler, and that attracts lots of tourists (photo: Nuno Costa, Sul Informacao).

Now, the Portuguese and Spanish local administration have made plans to build a bridge between the villages. This could help connect both sides. With a car it would take 10 minutes from village to village, instead of an hour. But which local would want that? If you would want to just cross the river, you can also go by ferry. This takes 10 minutes if you include the waiting. In general, there seems to be little exchange between the people of the two villages. The only ones crossing the border seem to be the sailors. There is one Spanish commuter regularly going up and down, and there are tourists, mostly hikers, crossing over by the ferry boat. 

The sparsely populated rural areas on both sides would not generate a lot of traffic. There is already a bridge over the Guadiana in the north (near Mertola), and one in the south (near Castro Marim), both about 30 km away. Sanlucar could benefit from the fire brigade and the health services in Alcoutim, if there wouldn’t be institutional and language barriers to be bridged first. 

The sparsely populated area on both sides of the river is connected by bridges. We have indicated them with arrows on the map: they are near Castro Marim in the south and Mertola in the north. Both bridges are located about 30 kilometres from Alcoutim and Sanlucar.

We are asking ourselves: who is really going to benefit from this bridge. Will there be economic development because of the bridge? From what sectors? There’s hiker’s tourism, some small scale agriculture, no mining or other industry. So, tourism might be one of the viable sectors. But then the question is: what do tourists want? We think the tourist who come to this kind of remote area wants good food, nice walks and a pleasant environment. 

The sound of a pleasant environment

A pleasant environment. Now we sailors and hikers get interested. Especially Peter, as an environmental scientist. He did a small ‘sound check on the spot’, as follows. He made a 10 seconds movie on a popular hiking trail. Just a random movie, so under the film you here the silence, with a footstep, some buzzing flies and a bird. This film-and-sound is recorded some 800 meters from where the bridge might be projected. We expect it will be a bridge with two lanes, with cars passing at 80 to 100 km per hour. So, then Peter put the noise of this kind of road under the same film-and-sound. Here under you see and hear the result. 

The first 10 seconds you hear the environment when you hike there.
The next 10 seconds is what you hear with a bridge near Alcoutim and Sanlucar with traffic.

This traffic noise is not loud. It would comply with the regulations about noise pollution, so don’t worry. But you would hear it. And it completely overwhelms the tiny sounds that a hiker, a sailor comes for, what many tourists enjoy. This region is one of the few where silence is not yet broken. Lucebert, a Dutch poet once wrote: Everything of real value is defenceless.  We would say: the sound of nature is at least vulnerable. Maybe we appreciate silence more because we have lived in big cities and we know what it’s like when you’ve lost it.

A revaluation

So, let us reweigh the plan of this bridge against the loss of silence in this environment. 

In the past decades, the roads to Alcoutim and Sanlucar have greatly been improved; they are small but good. You can easily travel to and from the tourist hotspots of Vila Real de Santo Antonio and Ayamonte on the coast. For tourists, there seems to be no particular added value that a bridge for cars might have. Also, the local inhabitants don’t seem to particularly need this infrastructure.

If you would really like to facilitate cars passing, a reaction ferry like here in Westerhuesen might be a better idea. 

Perhaps an elegantly shaped bridge for pedestrians and bikes might be of true added value. Especially if the bridge itself would be worth visiting, like the hanging Geierlay bridge or the Pedro e Inez bridge in Coimbra. They would have to allow for sailing boats passing through, so the bridge should at least be 20 metres high. Other ideas to strengthen the local economy might also be welcome, like cooperation on cultural activities, development of the regional cuisine, crafts but also attracting digital nomads like the island of Madeira is doing now.

A bridge for pedestrians or cyclists could be of added value, like the Geyerlei bridge (sources: justgo and pixeo)

What to do?

Concerned locals have started a website with information and a letter you can sign (in English, French, Portuguese and Spanish).

Everybody who is related to this area (also as a tourist) can leave his or her opinion at the


Good Food

Every day we make beautiful walks, just where we moor or drop our anchor. As a bonus, we find amazing food on our way.

The picture above shows a selection of vegetables, herbs and flowers from our friends’ garden in Calstock. This was in August last year.

In September, in Brittany, we were stunned by the delicious, fragrant passionfruit and the quinces that nobody seemed to want. Which is weird, because quinces are perfect for stews and marmelades.

The flower  of the passion fruit…

….and the fruit itself. You pick the ripe ones from the plant, it is the most delicious fruit you can ever get.

Bunches of quinces, ripe on the trees and inviting to pick,

In October, in Portugal , we saw a gem-like fruit that seemed much too beautiful to eat….

it was the fruit of the Medronheiro (Strawberry Tree).

From November, we walk in the area of the Guadiana river, the border river in the south of Portugal and Spain. Winter is actually a beautiful season to walk. It is pleasantly cool with 15 degrees Celsius.

In area around the Guadiana we see lots of almond trees along the roads and in the fields, with plenty of almonds.

You have to try first before picking them; some trees have sweet almonds, but some bear the bitter ones that you should be careful with. 

The olive trees were heavy with olives in all varieties. 

We met fellow sailors who have produced their own virgin olive oil. It took them three weeks to obtain 2 liters, but: it can be done. 

For cooking and making infusions you can find fabulous herbs anywhere. 

Fresh sage


Ever since we got on the Guadiana River, we have been seeing the orange trees, loaded with fruit. Harvesting season runs from September to March, so there is no hurry.

Walking along the Guadiana river, the orange trees invite you to pick a piece of fruit. 

In Februari, after some rainfall,  the oranges start falling off the trees.  And if no one comes to pick them up, they rot in the fields.

These are the most juicy oranges in the whole world. And water’s always near, which is important according to a widespread European fairy tale on oranges. So, in the open fields, we pick and eat as many oranges as we like. We cannot think of a more sustainable way to stay healthy.

the Mystery of Moisture

We are happy sailors on the Guadiana river. But happy or not, above the 30th degree latitude the winters are cold. It gets wet, also on board. A first sigh, a complaint. But the moment the first mildew or mould pops up, sailors start to fight the moisture with dehumidifiers and dripping boxes, with bottles of bleach, mighty moisture catchers, and fans and vinegar…. But not the smart sailors. They don’t need to, they prevented it. You want to know how?

Here we reveal this.

This is a typical winter morning on the Guadiana river. The cold water makes the vapor condensate till fine drops. You imagine how humid it is inside a boat?

The problem, the battle, and nature

Humid air feels uncomfortable. Living with moisture on board is like living in a shed. A humid cabin is difficult to get warm; it can easily double your energy costs.

So far you can survive. But once in November the first mould and mildew pops up, you are in shit. You smell it. You start sneezing. It feels unhealthy, and it is unhealthy. So, you start to fight it. You want to fight? The market offers you an endless arsenal of tools.

Here’s an article on how to spend your money. On  12-volt fans and wind scoops  to make Jeff Besos richer, or buy this if you want to make him richer in a more fossil free way. The ultimate arm is the dehumidifier,  because it has it all. This piece of technology costs serious money, it takes lots of space on your boat, and it consumes a considerable amount of electricity. And as a surplus, it needs maintenance, so you also have to work for the thing.
Not done yet? Here are plenty more arms to fight moisture, so don’t worry, you can fight endlessly.

From mould…
…To mushrooms (source)

In April you will think you won the battle, but you will experience reality when you go for your first sail and you open your sail bags. Black mould on your spinnaker, and sometimes even multiple servings of mushrooms in your sail bags and sails.

So, who won the battle? Nature!

In case you want to battle the sickening mould and funguses instead of preventing them, many funguses can be killed by spraying vinegar, or in more serious cases by chemicals, harmful to your health and your (our) environment.

If you battle the effects, good or bad, nature will win. For example, if you want to get rid of the effects of using fossil fuels, such as getting rid of the noise, the smell, the CO2, NOx and SOx, the fine dust, the worsening future for your children, then most people start to fight it. Then, the solutions are mostly paired with an awful lot of work and costs, and with slick but expensive technologies. And often you end up with half solutions and new problems. Don’t fight nature, because nature always wins.

Prevention, peace, and zero moisture

The best way to have no moisture is to prevent it. Just like we do on the Ya with the fossil fuel: we don’t like the effects of it, such as the noise of the engines, the smell, the bad future for your children, so we stopped using fossil fuel. Instead of the battle, prevention is like peace.

The preventive solution is not well known, because it is not exiting. There is nobody battling or working his ass off, and many times there is not even a demanding, complex, or expensive technology. A preventive solution is mostly a silent and cheap solution. There is actually nothing happening at all. For example, in case of a fossil free solution: there is no noise of an engine, no smell of fumes and diesel, no pollution of the lethal fine dust. You don’t hear, smell, feel, or even see the solution on the Ya. And, back to the moist, you can hardly find the moisture on the Ya.

How moisture is created and how fungus follows.

To start at the end of the physical process: moisture is condensed damp. Vapor is evaporated water floating in the air. Vapor condensates by three conditions:

  1. The more vapor, the more will condense.
  2. The stiller the air (no movement), the more it condenses
  3. The colder, the more it condenses.
In this film you see how the vapor becomes water again

Let us see what creates this vapor in your cabin. You can see the steam from your cooking water kettle. Or you see the dense steam from the pan you cook the potatoes in. For 15 minutes the dense steam is spreading into an invisible vapor.

It looks like this is a lot, but there is much more created by your gas (butane, propane, methylated spirits) stove in your galley or kitchen. Every liter of gas will create an average 7 liter of vapor!

You usually cook when it starts getting cold outside, so you keep the cabin closed. The vapor fills the air and goes into your mattresses, pillows, sleeping bags, linen etcetera. The vapor does not condense yet, because the temperature of the air and of the boats skin is still warm.

Inside the boat, all people breathe. Each adult in total exhales about half a liter of water till the next morning.

During the night everything cools down. The cold air hits the windows and the skin of the boat. Then, the vapor in the air cools down and condenses, leaving a film of water on everything. It gets into your cushions, your cloth and if a lot, it leaks down between your carpentry.

Funguses are sickening, but under the microscope they look beautiful. source

What helps is to evaporate it again. You can do that by heating up and by ventilation, to blow it away. That works on the open surfaces, but in cushions, corners and carpentry the moist remains. This is the ideal habitat for mould and all sorts of mushrooms and funguses.

Check here for the diseases mould brings you. The very moment you smell the first mould, it brings up the instinct to battle it. Don’t. You will lose it. Do better: clean up and prevent it from now on.

How Ya prevents moisture

We cook with a water cooker with automatic stop. So, the steam is limited to perhaps 10 seconds. The bulk of our food, we cook in a pressure cooker. The moment the pressure is on, we put the cooker in our ‘hay box’, an insulated box, where it slowly cooks till it is done. No steam at all. Most important is, that we don’t cook on gas. With the luxury of the electric engines/dynamos, we have a big battery bank. So, we have plenty of energy to cook with an induction cooker instead of a gas stove. This truly saves a lot of vapor.

An induction cooker brings your vapor output back to zero. You can start your evening in a dry climate.

The vapor we have while cooking, we let go directly through an open hatch. Cold is not a problem, because we have a hull with a panorama window. So, in the late afternoon and early evening, the sun shines in fully and heats up our cabin. This way, we can start our evening with a low humidity.

Every morning and evening the sun comes in abundantly and quickly the temperature rises to a comfortable level.


However, you can prevent what you want, also in the Ya the vapor builds up with every time we exhale. The two of us blow a liter of water into the air in an evening and a night. So, every morning we open all hatches and ventilate well, for about half an hour. This is refreshing.

Moisture can accumulate in all closed areas with still air. So, we have put little vent outlets under every couch and cupboard. You drill a hole of 4 cm and glue the outlets in.

Under every cupboard and closet you need at least one ventilation hole.

But the real miracle is that we don’t have any moisture, mould or mildew on the carpentry, the ceiling, or anywhere else on the skin of our cabin. For many sailors this is a miracle. This is the miracle created by the insulation. It is 11 cm thick PIR foam and this makes the skin better insulated than the walls of a regular West European house. In The Miracle of Insulation you can read all details.

A cheap piece of bubble plastic as a ‘double glass’ taped on the hatches and port holes, prevents condensation and still allows 90-955 sun light and heat into the cabin.

Windows on the Ya and what we do

All windows and hatches are single glazing . While here, in wintertime, they should be at least double. I remember I discussed this with the manager of the marine glazing company, but he only looked at me with glassy eyes; this was perhaps too visionary.

So, during this winter we simply put a cheap bubble plastic on the hatches and port holes with some tape. We still have the light, and the heat of the sun through it.

Living on board comfortably in a winter, means your ship must seriously be insulated. The Ya is completely insulated, except for the windows. Every morning we strip our 2 X 5 meter cabin.

For our long single glaze (polycarbonate) windows, we simply accept that we take 5 minutes every morning to strip the condensation off. We remove about a quarter of a liter.

The top of the locker of the sails is not thickly insulated, and it has an open connection to the cabin. So, slowly, our sail bags get humid. When the winter sun shines and the sky is blue we put the bags open on deck. In that environment the air is extremely dry.

The mystery of moisture revealed

Moisture on board is caused by adding vapor to the air, that will condensate on cold surfaces. This is a great habitat for mould, mushrooms and other sickening stuff.

Fighting the moisture costs, time, money and is never ending. Best way is prevention. Prevent by:

·       No combustion of fossil fuels inside. Especially gas cookers are very energy inefficient and create a lot of vapor.

·       Insulation. The more seriously insulated, the better things stay warm enough to prevent condensation on it. Check here how it was done on the Ya.

·       Ventilation. Refresh the air in your cabin and let the wind blow through it for a while. And put ventilation holes under your cupboards, berths, closets.


Fossil in paradise

We feel privileged to be on Guadiana river. We are on the Spanish side now, where there is no shore power, but a magnificent view on Alcoutim on the Portuguese side.

Sunny Alcoutim (Portugal)

Until, after some days of fog and rainy weather, we noticed our batteries were on lower capacity than was to be expected.  Trouble in paradise! Was this only the lack of sun and wind?

Gloomy weather on Guadiana River

We realized that our batteries were deteriorating after 7 years of faithful service. Not unexpected, but nevertheless: bad news. Especially because we have a lot of them.

Onboard of Ya we currently have 24 lead-acid batteries

But, never waste a good crisis. We have been carrying around 25 liters of gasoline and a small generator the size of a sewing machine for in case of emergency.  With too little sun and wind and lacking shore power, we decided to start using it.

One of the smallest generators available

During the circumnavigation we never had to use the generator, the trip was truly fossil free. The gasoline is now 5 years old. So, we had to filter it several times before we could use it. 

Fossil in paradise

We are grateful that this now helps us through the windstil, cloudy periods on the river. And we are grateful to our neighbours for not complaining about the noise. But, oh boy, what a nuisance, this fossil in paradise. It stinks, it disturbs the peaceful quiet on the river and we have had to repair it 2 times already because it had hardly been used. 

Generators need maintenance

We pray for the sun to shine and the wind to blow so we can use the generator as little as possible. As we write this we see the meter jump to charging 400 Watts on wind and sun so this is a lovely day.

Ya in Sanlucar de Guadiana with the SilentWind (our camera is quicker than the human eye, it was spinning!)

We have started the search for new batteries to be able to continue our fossil free life.

In one of our next blogs we will tell you about our search and all that comes with it.

Nortada brings silent wind

The Nortada, the Portuguese Northern Wind, brought us to the Algarve. We have been here for a while now, happy victims of the Guadiana Glue. Since our wind generator broke down, we wanted to select a new one. Which one? In this article we compare the three most used quality wind turbines: Air Breeze, Superwind and SilentWind.

Airbreeze (with SilentWindblades), SilentWind and Superwind

We compare these three wind generators because they are universal. They can handle all batteries, can be combined with solar panels and other generators, and they are available in 12, 24 and 48 Volt. They are often used on yachts and they are all good, high end generators.

We chose for the SilentWind for its light weight, low noise, the power in also the high range, and the low maintenance.

The yield is in the height!

If you really want a wind generator to deliver, then it needs height. Don’t put it on a 3 metre pole on your boat, but put it higher than 5,5 metre, away from wind obstacles. Then it delivers double, because that is where the wind blows.

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This is the Zaan at Zaandam from Claude Monet. The 17th century Holland was packed with windmills, used for all sorts of industry. They determined, when higher than 5,5 meter, the wind became significantly stronger. This rule could very well be sufficient on yachts.

This ‘higher-than-5,5’ metre rule dates from 17th century. They figured this out in the time that building high mills was difficult, while the wind in Holland was crucial for the industry there. In those days, the Zaanstreek was the innovation centre of Holland, the dominant and richest country of the world. It was full of windmills, for sawing wood, grinding grain, and they were pumping the water out of the polders around Amsterdam. They could use every sigh. This ‘higher-than-5,5-metre’ rule nowadays is interesting for us sailors.

The diagram on the left shows the windspeed windward of an urban place. On the right, you see the diagram of the wind speed on the lee side. A windmill must be put much higher than the disturbing buildings to catch good wind. (Source: Fernando,J .(2010). Fluid Dynamics of Urban Atmospheres in Complex Terrain. Annual Review of Fluid Mechanics, Vol 42, s365‐389)

Check the picture above. The wind blows from the left to the right. On the left side you see a diagram of the ‘clean’ wind. The wind is there if not too close to the surface.  The wind blows over the buildings and creates turbulence above it. On the right side you see the influence of these obstacles.  For good wind, you have to be far above that ‘stuff’. This also underlines the +5,5 meter rule from the 17th century, when obstacles in the field were not higher than the cattle and the grain. And this corresponds with our yacht: a hull on the water, with a railing and stuff on deck. So we’d better stick to that +5,5 meter rule.

If ever you want to remember anything about the yield of windmills: the height is essential. A cheap windmill put on 7 meter, gives a a far better yield than a high-end windmill put on 3,5 meter.

From here we go into the nuances and details.

The windmill on the Ya is over 7 metres high. There’s metres free of obstacles, and you need that to get good wind generation

More height – less weight

A sailing yacht should not capsize. The ‘Ya’ is an ocean approved yacht and complies with the highest standard; even with the mast top blown into the waves she still self-righting. So, all high things on board are necessarily light things.

There are two pretty light wind generators. The lightest is the Air Breeze (5.9 kg). SilentWind a bit heavier (6,8 kg). Heaviest is the Superwind (11,5 kg).

The Superwind is too heavy for a yacht like the Ya; we would have to put it two times lower and this is close to nonsense. But it is a good turbine for a bigger yacht.

The power – it is in the range, not at the peak

The peak power number only gives an impression for a first orientation. All three wind generators are in the range of a couple of hundred Watts. Instead of the peak power, you must look at the power curves. Then you understand the power of a windmill and what suits you.

The Air Breeze (red line) may be the smallest in peak power, but this light mill delivers already 75 Watt at 15 knots wind speed, which is of great value in the leisure sailor’s wind. And there is an extra power peak in the 6 and 7 Beaufort (when there is mostly overcast, so no solar power). You always sail in strong winds? Take the Air X Marine (blue line).
The SilentWind continues its increase till 28 knots of wind. This When over 7 Beaufort, it supplies an awful lot of electricity. In this graphics you also see that generating on high voltage is more efficient; the 48 Volt version yields nearly 25% more than the 12 Volt version.
The Superwind is heavier and delivers slightly more from the first cut-in, and from 25 knots of wind (12 m/s) it delivers 350 Watt continuously. The internal regulation dictates that the 12, 24 and 48 Volt versions all deliver the same 350Watts.

Shrieking, madness….and then silence

We are cruisers. We love nature and the silence. We want our wind generator to deliver energy, not the noise.

All three windgenerators have 3 blades. This is a compromise between efficiency and noise. Interested in the technological reasons why? Rosie explains it simple and straight here.

On the Ya we started with the Air Breeze with the standard blades. From the first cut-in, it started making noise. First you like it, because it delivers. But when it really starts delivering and nears the 15 knots of wind, the blades produce a high shrieking sound. The first neighbour started to complain. At 20 knots of wind the neighbours got angry.

Then we discovered the silent blades. Made in Portugal by SilentWind. A high-end product, just as the price of over 300 Euros. But it was worth every penny. Now the same Air Breeze was making a bit of a whistle till 10 knots, a more serious whistle with more speed, and when the wind is somewhere between 15 and 20 knots, the wind generator’s noise drowns into the ambient noise of the wind blowing through the rigging of the boat.

The Air Breeze with the original blades. When equipped with the blue low noise SilentWind blades, you maintain a good relationship with your neighbours.

Now we have the SilentWind. When the rotation is slow and you listen well, you can hear the sound created by the magnets or the new bearings. At 8-12 knots you hear a light low whistle and when faster it becomes a friendly lower tone with more volume. When over 15 knots, the noise drowns into ambient wind noises.

The Superwind you will not hear from 20 knots of wind. I listened many times to this mill in several situations in light winds, and it is really low noise. But nothing beats the SilentWind.

Brakes and no brakes

All three can be switched off manually, for example when there is not enough wind. The switch simply makes a short circuit. The Air Breeze and SilentWind also use this short circuit brake to prevent too much speed, which is near hurricane.  Before the blade tips would reach bullet speeds, spin out of control and could be ripped from the turbine, the electronics create a short circuit and the blades will slow down to a near stop.

The SuperWind solves this differently, with smart blades. From 25 knots the blades automatically start to adjust their pitch and the rotation speed will not increase. So, in a severe storm, when there is not much sun for your solar panels, the Superwind keeps on generating energy for you.

One could say that the extra moving parts of the Superwind blades have more chance to fail than the simple fixed set of blades of SilentWind and Air Breeze. But this elegant mechanical solution is perhaps safer than the electronic shut off, because also electronics can fail.

Every windmill can be pre-set to stop generating electricity when a certain voltage is reached. Air Breeze and SilentWind simply use the same short circuit brake to prevent overcharging. Since Superwind does not have this brake, all the excess electricity is regulated to go into big capacitators that will get warm, or even hot, and will be cooled by the air around it in your engine room. I don’t like that for leisure sailors. In wintertime the consumption is low and the battery full, while the winds are strong. Then, when nobody is on board, the capacitators in the engine room or cabin cupboard get very hot. It doesn’t give me a safe feeling.

The Superwind

Keep your maintenance low

Superwind designed the mill to keep the maintenance low. The blade pitch against too much RPMs and the double bearings are two examples. Great, but all together it became too heavy for us.

Our Air Breeze broke down. It did not work properly in the medium wind range. Was it the circuit board? We lowered the mast, unmounted the shaft, et cetera and took the circuit board out. We sent it to the service. It was renewed. We remounted everything, put the mast up again, and it ran well. One week later, the same problem. We lowered the mast… to cut a long story short, we lowered and raised the mizzen mast six times (Thanks to Piet, Tulga, IJsbrand, Henk, Jaap, Mick, Inez and others). We also renewed a chip up there, and other things.

The electronics of the Air Breeze are extremely simple. Great, I love KISS. But they are in the housing of the turbine. Too high to keep an eye on it or maintain it.

Then one morning, we were on the river Guadiana and I saw a strong breeze running over the water towards us. I looked up the mizzen, and saw the Air Breeze hardly responding. I knew, this was its last breeze. Our Air Breeze was no more. We declared it our late Air Breeze.

After these ups and downs, I learned what had to be down. That’s chips, diodes and circuit boards. They don’t belong in the top of your mast, where the rain and moist and salt from the sea reign and you can’t look after it. If you want to keep your maintenance low, then keep it low. Superwind and SilentWind put the electronics in a box (converter or MPPT) and you mount that box in your engine room or cabin or any other dry place. Ofcourse it can break down, but in that environment the chance is smaller and the (preventive) maintenance is easy there.

Why the SilentWind is Ya’s pick

Weight=height. On the Ya the windmill can be put on 7 meters high, on the mizzen mast. If…. the generator doesn’t weigh too much. The 6 kilograms of the Air Breeze and the Silentwind don’t influence the stability of Ya. The Superwind with its 11,5 kilograms should be mounted half way. But on 3-4 meters height there is simply not enough wind to justify such a high-quality piece of equipment.  

Silence. All three are reasonably silent. (if the Air Breeze has the low noise blades). On the other hand, if you are on anchor somewhere in the middle of a creek enjoying the singing of the godwit, bluefinch and specked spoonbill, and then a light breeze picks up, you will enjoy the off-switch of your wind generator.

Which is the best on low noise? My private opinion is that the SilentWind -what’s in a name- beats the Superwind.

Power range. All three deliver well in the critical wind range we like to sail in, or when we anchor in a more open bay. The Air Breeze is best in ‘our’ leisure sailors wind range and falls back in the higher regions. The Superwind is doing about the same, but is cut on 350Watts from 25 knots. The SilientWind continues in the high range. We are also interested in the production in stronger winds, when the weather is bad and our solar panels don’t deliver. Then the 12 Volt delivers continually 420 Watts. The 48 Volt version -which is of our interest- delivers even 520 Watt, so much better than Superwind (350 Watt) and the Air Breeze (200 Watts). Our battery capacity is big enough, it is seldom full, so let it all come in, SilentWind!

Regulation You can look deep into the regulation. We love KISS, and then the Air Breeze comes close with a simple circuit board built in the mill. SilentWind’s regulation is based on the core business of the wind generator: to take all energy it can get from that wind, from the cut-in speed to the safety limit at gale wind. The only disadvantage is that you have a big MPPT in your engine room.
I do like the blade pitch solution of the Superwind to keep on running smooth in even a hurricane. But I don’t like that the mill keeps running when the battery is full and the capacitators can get hot. Batteries are full when there is no consumption, so mostly when nobody is there. Then we don’t want critical hot things on board.

Low maintenance. A special word to Superwind. They have put a lot of attention to durability and low maintenance. Unfortunately, this is also the reason that it became too heavy to be effective on the Ya.

I see maintenance, preventive or repairs, as a daily custom for the sailor. But our Air Breeze signed its death warrant when it had to be lowered from the mizzen for the 8th time to check the circuitboard. The SilentWind (and also Superwind) keeps this delicate stuff in the converter or MPPT, to be mounted low, e.g. in your engine room.

Conclusion: We chose SilentWind. Please mail if you have any comment. We’re curious what you choose and why!

Plastic waste and art

In Alcoutim, we saw a beautiful creature on the shore. Very big and bright. She is called: LONTRA. 

Plastic Otter, 2020, Bordalo II, created out of plastic waste for the Festival do Contrabando, Alcoutim. Photo: Chris Costa

The artist created her out of waste plastic. He is called Bordalo II. On his website we read why he makes this kind of art. “The excessive production and consumption of ‘stuff’ results in a constant production of garbage (…) and leads to the destruction of the Planet.” Bordalo II uses this garbage as raw material in the construction of small and large scale pieces that he has spread around the world. They bring the universal ‘manifesto’ against waste. 

Bordalo II also makes more provocative art, which you might find interesting. So here are two more pictures:

Selling The Truth, Lisbon, Portugal, 2015. Photo: Bordalo II


Mourning The Oceans, Covilhã, Portugal, 2014. Photo: Bordalo II

We were quite impressed by Bordalo’s work and hope you like it too; his message speaks for itself.

The miracle of insulation

The Ya spent Christmas on a beautiful spot in the Guadiana river. In the morning, we could hardly believe what we saw: there was a beautiful thin layer of frost on the deck. Apparently, it had been freezing. Inge quickly took a picture and went straight back into the comfortable cabin of the Ya. Contrary to most yachts, Ya hardly ever needs a heater to keep it warm inside, even in wintertime. Is this a miracle? No. We will tell you our secret: it‘s just about three things.

The secret of Ya keeping warm inside in wintertime is in three things:

  1. Insulation
  2. Insulation
  3. Insulation

1.    Insulation – a lot, and neatly built in

Before we started with the carpentry, the hull of the Ya was insulated. This was done very precisely with high quality foam, called PIR foam (not PUR!). It is built up in layers up to 11 cm thick. Every foam plate is tightly closed to the other, with some caulk or PUR in between. So, there are no heat leaks.

Before and after the insulation: Tsjerk built the PIR foam up to a layer of 11 cm thick. As a real ships carpenter, he sealed all seams with great care, so, no heat can leak through and no condensation can occur.

2.    Insulation – PIR as an affordable quality foam

How good is this PIR foam? Well, it is a great insulator and very affordable, and it is self-retardant, so it slows down fire. In the table below you see some numbers.

The Lambda number says how many Watts of heat goes through the material if it is 1 m thick and when there is 1 degree (Celsius or Kelvin) difference on each side. So, the lower the Lambda, the better the insulation. As you can see, the very expensive Vacuum Insulation is doing best. The PF Quod Core (0,015) is second best, but it can only be applied flat, and it is rather expensive. And the third best is PIR: this can be used on yachts. It is also self retarding. Materials like cork or expanded clay are doing much worse. Better not use them on yachts, they also weigh a lot.

On board of steel yachts, often glass wool is used. It is easy to put it neatly in any corner. But, once wet, it insulates only as good as the water in it. And it can go down and hang, a disadvantage. When it is dry, it insulates OK. But PIR does that better and PIR can’t take water (condensation). Disadvantage of PIR is that you need to work very precisely. Every open seam is a heat leak and that also creates condensation.

The final column in the table shows the resistance value (R-value). As the Lambda is a theoretical number, the R-value shows the effective heat resistance when the insulation is used in houses, caravans, boats. The higher the R-value, the better. It confirms that PIR is the best affordable choice.

 MaterialAverage LambdaR-value for 100mm thickness
 W/(m-K) M2K/W at 100mm
Brick (sand lime)0,80,125
Glass fibre 2,5
Core cell foam 2,6
Cellulair glass0,0442,78 
Expanded clay0,044
PF/ Quad Core0,0155,56 
Vacuum Insulation0,004223,8


3.    Insulation – to get comfort

On Christmas night it was minus 3º Celsius. We were having a Corona-proof dinner with some fellow-sailors. It was nice, we had fun, lots of olives and almonds, little alcohol and no heater Then, our friends asked where our heater was. Well, somewhere packed deep down in a bilge; we can’t remember using it. Yet, the atmosphere on the Ya felt as comfortable as in a house, or even better. How is this possible?

Now, let us compare the insulation of the Ya with that of a normal house built in the 70’s or 80’s. How well is it insulated? Or, to put it technically: What is the heat resistance of the house’s walls and the Ya’s skin?

Suppose you live in a house with brick cavity walls and 5 cm of rockwool insulation. The two layers of 10 cm bricks each have an R-value of 0,125. So, this is 0,25 in total. 10 cm of rockwool has an R-value of 2,6. Your house has 5 cm, with an R-value of 1,3. So, for the house the total R-value is 1,3 + 0,25 = 1,55 which is the total heat resistance of your wall.

 Here you see the intersections of the skin of the Ya and a cavity wall of a normal house. The heat resistance -the R Value – of the skin of the Ya is 3 to 4 times higher!

Now the Ya

The skin of the Ya is made of 6 mm of glassfibre, 20 mm of core-cell foam, then 4 mm of vinylester/glassfibre. In addition, on the inside the skin is covered with 110 mm PIR foam.

So, the skin has glassfibre (6mm +4 mm) 10 mm. The R-value of 10 cm is 2,5, so the R-value of 1 cm = 0,25. It also has core-cell foam 20 mm. The R-value of 10 cm is 2,6, so the R-value of 2 cm = 0,52. On the inside: PIR foam 110mm. The R-value of 10 cm PIR is 4,4, so the R-value of 110 mm = 4,84. So, for the Ya the total R-value is 0,25 + 0,52 + 4,84 = 5,61.

The total heat resistance of the skin of the Ya is more than 3 times higher compared to an insulated house. No miracle Ya keeps it warm inside in wintertime.

Sun Power for Your Shower: the Heat pipe panel and a multipurpose system

The sun power can be used to really heat everything.  In this last episode show we show the heat pipe panel, for even hotter water. And on top of it, we show a multi purpose system to really make a beautiful water heating system on board, or at home.
Too technical? Then go to the end of the article. There you find a picture with a cute model (says Inge) trying out the shower!
This Heat pipe panel becomes hot by the sun. Each pipe is dark, and surrounded by a transparent pipe, so with a vacuum in between for splendid insulation. There is a little bit of fluid in each pipe. This fluid will evaporate. The hottest damp will go to the top. There a cooling fluid flows along the outside skin, taking the heat and cooling the skin down. So the damp inside the top of the pipe condenses and runs downward to get heated and evaporate again.

The heating panel collects the heat and gives it to a cooling fluid. The fluid circulates through (or around) the boiler and gives the heat to the colder water. But that is just one function. The beauty of this system is that it is a multipurpose system: for heating and cooling. In this film you see a short description.

If you want to know more, check the drawings and the text here below.

The Heat pipe in a basic system

This closed circulation system is filled with cooling fluid. The circulation pump  makes the circulation. The fluid goes through the heat pipe panel. Only a first sunray through a cloud will heat up the water there.

The fluid then runs to the boiler, where it goes throught the boiler spiral , so that it heats the water in the boiler.

Then it runs back to the panel.

To a multi-purpose system

You can put a stove in the form of a radiator on board. It works sufficient in autumn; it will not give much heat.
There is a valve before it in the circulation system and you can choose if you want to let the fluid go through the radiator. If the valve is closed, it runs further.

You could for example use this stove in the evening, using the heat from the boiler. With an extra valve you close the heat pipe panel out of the system so you let the circulation go from the boiler to the stove and back.
And you can do more. Here we show it on video:

A multi purpose heating system with Heat pipe panel, stove, boiler, and motor built in. Also the motor, because you can cool the motor, or use your diesel to heat.

You connect the circulation system of your motor into the circulation system. So, the motor is also a heater. An electromotor is highly efficient, so you won’t get much heat of it, but it works more efficient if it stays cool.

Especially for combustion motors it is interesting to build its cooling system into your cooling system. Combustion engines are terribly inefficient and the mostly produce more heat than propulsion. A diesel engine converts about 50% of the diesel into heat.

And on the other hand, your system can warm the motor up. A cold running combustion engine wears the engine out, so why not first heat it up? It saves your engine from wearing out.

Regulating the system

To get a high heat intake from your heat pipe panel, the circulation pump should run slow. That is the main thing to regulate. You can put a by-pass in it with a valve to lower the flow. Or if you like it the electrical way, put a resistor in your feed to lower the power to the pump. There are also electrical regulators with a pot meter.

Put many valves in the system, so that you can do whatever you want, such as:

  • Heat your boiler with the heat pipe panel
  • Make your stove/radiator work with the heat of the boiler
  • Cool your (electric) engine and controller, or your combustion engine
  • Heat your boiler and/or your stove with your engine.

When you want to heat in the night, put a valve before the heat pipe panel, to prevent loosing heat there.

Simply use valves that you can open and close by hand. Just make sure that there is a flow in the system, because the circulation pump must be able to do its work.

Often, you see three-way valves in such systems. These valves always give way to or one way, or the other way. Disadvantage is that you must choose. You swith or/or, and sometimes you want and/and.  For example if you want the radiator to be warm and the boiler, donot use a three way valve, but put just regular valves in, as drawn. Advamtage is that you can even regulate how much you want to feed to e.g., the radiator, and to the boiler. Or, when the motor produces heat, you open that valve.

First do it manually, and when you are experienced, you automize the options you want. You could put sensors everywhere in the system and connect them with valves. But that could make it much more complex than you want. Start with the basics first.

The system can be drawn very schematic, but as you can see here on board Jaap his yacht, is that you have a spaghetti of hoses, lines, pumps and wires near your boiler, simply because you put a boiler in your bilge as big as possible so the space is so small for everything..

The test

With this heat pipe added, you can get really hot water and not only during summer. The spiral heater is doing great, and you can build it yourself. But the heat pipe panel is directly handy to build in. and it looks like it can take more heat out of the sun. Great to get a big hot shower, even in winter time.

The test: showering all over everything!

You want to know more? Email  

From the Ya we wish you a healthy and merry Christmas and a fossil free future!

This is the Ya sailing fossil free south of the Algarve, Portugal, October 2020.  ©Vernoomedia

Because of COVID we started our fossil free tour around the world later than planned. But, never waste a good crisis. COVID can be a turning point in the fossil fuel consumption.

More and more of us see, that working at home works. In 2020 there are more electric cars sold then all years before 2020. In some countries the CO2 emissions lowered. Since 2020 is again a year where we break meteorological records on high average temperatures, more and more people become aware of the climate problem.

Good intentions for 2021? Be the one of the growing many to act. Reduce your fossil fuel consumption. Insulate your house. Only take the car if you need to. Stop cooking with gas, put solar panels on your roof and cook with an induction cooker. Ask your local government to stimulate solar panels on buildings and industrial quarters. Ask your MP to reduce or stop the aid to fossil companies such as airlines.

It saves money, and it is a start to stop compromising the future of our children and grandchildren.

Wherever you are, we wish you a merry Christmas in (fysical or virtual) good company and a happy, healthy and fossil free 2021.