The yacht

A. The windmill is the first generator of energy. The windmill must be put over 5 meter high to be reliably effective, because the higher up it is mounted, the more wind it catches. When we sail upwind, the windmill always works great and delivers enough to compensate the loss of the waterpropellers. Learn all about it…

B. The Autoprop propellers are set in vane mode when we sail slowly. But as soon as our speed through the water reaches 5 knots or more, we use them for hydrogeneration. Autoprops are adjusting continuously to the most efficient propeller pitch and transfer rotational power to the E-Tech dynamos. These dynamos are the electric engines, but we switch them to the generation mode as soon as we sail. This way, we generate hundreds of Watts when making good speed. Learn all about it…

C. The Fibercon sails make the real motor. They can generate over 20 kW of power. The sails deliver the speed to make the  Autoprops and dynamos run. Especially when the wind is light, we have to mention the Parasailor. This sail empowers the yacht in an easy going way and gives her a continuous 5 knots or more, enough to make the Autoprops deliver good energy.

D. The carbon masts (main mast and mizzen mast) are much lighter than the regular aluminium masts. This saves a great amount of weight. Every kilogram less in the top of the mast saves 34 kilograms of ballast. So the boat remains light and it is easier to make good speed.

E. The big windows bring a lot of light inside, and, more importantly, when the sun is low, they let in a lot of heat! About 80% of the sunlight converts into heat. This happens with every morning and evening sun, just when it is colder, so when we need it most. Nice in the morning and it saves a lot of extra heating in the evening.

F. The solar panels work as biminitop over the cockpit. They are thin and cool well, so they work great, also in the tropics. Learn all about it…

G. The (walkable) panels on deck can’t cool well, but they kick in when in Northerly latitudes, where you also need them. The side solar panels in the windows are mounted there, because they block the view in e.g. the toilet or a cubboard. Learn all about them.

H. The hull skin is made of foam and glass/vinylester. On the inside, an extra 11 centimeter of PIR foam is applied to the skin. Now we have an insulation comparable to a house with insulated cavity walls. We hardly need energy to heat up in the evening. Learn all about it…

I. The lead acid batteries contain the energy, normally consumed by an average European family in an average week (about 70 kWh or 1400Ah). If there is no wind and you need to go to the shore, you can motor 48 hours making 2 knots. The batteries weigh a lot and this helps for the stability – it saves us lead as ballast.

1. The navigation lights are LED lights of LOPO Light. They reduce the energy with more than 80% compared to the ‘yellow’ argon light, or 40% compared to halogen light. These LEDs have about 50.000 working hours, are much smaller, and lighter, which is beneficial for the stability that high up in the mast. [/su_column]

2. The broadband radar consumes 40 to 50 times less energy and is 3 times lighter than the regular pulse radar. And, when switched on, it directly starts working. A great radar for sailors, especially leisure sailors.

3. The two E-Tech electric engines deliver 6,5 kWatt each (together about 19 HP) with about 90% efficiency to the Autoprop propellers. The self pitching Autoprops are the most efficient props, according to various research in sailing magazines. They can save you up to 70% of energy in your propulsion. But more importantly (see B), when sailing, we switch the E-Tech drives to dynamos and also then the Autoprops run in the most efficient generation mode.

4. The navigation equipment consists of a sounder, log, wind meter, GPS, AIS, radar, all shown on a plotter in the cockpit. All this is using 30 to 50 Watt. Separately we have a second system on a tablet, showing AIS, GPS, which is good on the ocean and consumes 5-15 Watt.

5. All interior lights are LED. Most lights use 2 or 3 Watt, so it hardly consumes energy.

6. The induction cooker can take 3500 Watt. This is a heavy user, but always 50-55% less consuming than a regular propane/butane cooker. It saves a lot of humidity and moist, see the Heating chapter. And no gas on board is much safer.

7. The ‘hay box’. As soon as our rice, vegetables or pasta cooks, we take it from the induction cooker and put it in the ‘hay box’. This is an insulated drawer (not shown in the drawing). This way, we let the food cook in its own heat till it’s done. Safe, and we now cook with an 80% reduction of energy!

8. The microwave oven is great to quickly heat a meal. With its efficiency of 70%, it is far more sustainable than using a frying pan to heat up your bite. There is also a regular oven in it. Great as a stove, but if we want to make a bread, we use the bread baking machine, which is 3-4 times more efficient.

9. The water cooker has a level indicator, which is the best invention to save water and energy. The cooker takes a lot of power, about 2000 Watt. Because it is double insulated, nearly all the energy goes into heating the water. So the water is heated quickly, and we use only 20% of the energy that you use when taking a kettle on a gas stove!

10. The fridge/freezer is much better insulated compared to normal fridges or freezers, especially the ones in yachts. The box is completely packed in about 10-15 cm of PIR foam (high quality foam). The compressor is the smallest on the market and can use 30 Watt, which it scarcely takes. Because of the thick insulation, the fridge/freezer stays a small, neglectable user, also in the tropics. Anecdote: Originally we meant to design a fridge only, but when testing, all our food froze! So we made a freezer/fridge of it.

11. Power electronics consist of the Studer inverter/converter and the Envitron measuring system. This is what people need: direct, clear information. They get it in basic simplicity and believe it or not, the funny thing is that the numbers on the display do turn people into real fossil free addicts.

12. On board is a separate washing water and potable water system. The deck of the Ya is one rain catching area, and the water can be drained to the washing water tank. From there, we can press the fresh rainwater through a silver ionizer to preserve it and then store it in the drinking water tank.

Specifications Sustainable Yacht

TypeSustainable Yacht
Length10.10 m34.5 ft
Beam3.96m12.8 ft
Draught0.70/2.70m2,3/9 ft
Displacement8,5 tonnes (empty); 10,5 tonnes max
Materialvinylester/glas on foam
Airdraught17,5 m
CE approvalA (Ocean)
Mizzen5 m2
Mainsail38 m2
Staysail20 m2
Jibb28 m2
Genaker52 m2
Parasailor64 m2
Storm jibb6 m2
Sustainable Yacht has rectractable centerboard. She is yawl rigged, has a 2.4 meter extendable carbon bowsprit for the jibb or genaker and has a 3.8 meter carbon spinnaker pole for genaker or Parasailor.

General Plan Sailplan Line Plan

Stability Plan Polair Diagram

Energy Balance Datasheet Energy

The Energy Balance

Here you find a number of in-depth articles how the Ya is built up to a fossil free yacht. We start with the generating equipment and then we treat the usage.

The windmill

Next to the solar panels and the dynamos/propellors,  we have the windmill in the mizzen mast.

No matter what windmill you choose, just first consider the thing should be high! The reason is: the higher the more wind. See the drawing here under. Especially the first meters count a lot. Windmills on 2 meter poles – leave it, or buy at least a very cheap one, because it will not work the way you want it.

The windforce increases seriously with the height.

An old Dutch study for the position of the old fashioned windmills from the 17 th century and on, stipulates that the wind has increased to an effective level  at a height of 5,5 meter and higher. So the windmill of the Ya is mounted on the mizzen mast 7 meters above the water. Which is about 6 meters higher than the aft deck. 

The windmill of the Ya is marinized and light weight, 6 kilo to be precise. This weight is the only reason that it is not mounted on the top of the main mast. The capsizing angle must remain over 120 degrees (CE-A approval). An alternative place could be on the spreader and then with a spherical fence around it to protect it against the sails. Then you will need a windmill on each side, in case the mainsail covers it.

Numbers and practice

A good windmill starts rotating at a wind speed of 3 meter per second, which is about 6 Knots. But realise that it produces not even 1 Watt then. Physics laws dictate that with little wind speeds, you can only get little power. A good windmill has an efficiency of  about 20%. Betz’s law tells that it cannot get very much higher. The logics of Betz: the more the wind takes on energy, the less the speed of the wind will be.

Generally, you will be happy with a windmill from about 10-12 knots, so from 4 Beaufort. A good windmill generates 50-70 Watt then. The Ya’s windmill has low noise blades. This costs an extra 200 Euros, but it saves a lot of noise, especially when you don’t want to hear it. You can hear the first light sound at 7-8 knots. Up to 10 knots I switch it off, because I love silence and you hardly have energy from the mill. When it gets about 15 knots the mill delivers about 100 Watt. The noise would be irritating, but at that level the wind starts to make its noise through the rig, so the noise is relatively no problem anymore. At 20 knots, the windmill’ noise disappears in the ambient noise.

The peak power is 400 Watt. This is in the 8 Beaufort range. At 7 Beaufort it already comes close to the 350 Watt. With more wind, it automatically switches off in its safety mode; the windmill breaks by itself and rotates very slowly then.

Advice is to buy a quality windmill, marinized of course. Silent blades are worth the money on your leisure yacht. In my windmill all parts are in the housing. Advantage is that you only need a two wired cable and you can connect it directly to your electricity networks. Disadvantage is that electronics outside at sea quickly break down. So next time I would buy one that has its converter down in the engine room and I will pull a three wire cable to the windmill.

The windmill in the Energy Balance

The windmill on board the Ya is the smallest supplier in comparison with the solar panels and the props/dynamos. In the Energy Balance here under you only see the average, which is not very meaningful.

The essence is that the windmill is complementary function. With little sunshine and much overcast, there is mostly a fresh breeze. So the windmill delivers when the solar panels hardly give energy. And, when sailing on upwind courses, we have to put the propellors in vane position, because we need all the power. Then, with the apparent wind seriously blowing, the windmill makes the lack of the props all good.

Generation#Watthr/daykWh/day
Windmill 400 Wp1150203,00this is an average; upwind is much more; downwind much less
4,8m2 Solar bimini 3*230Wp321663,8930% of Wp during 6 hours
3,6 m2 Solar deck 440 Wp38851,32less power due to heat and shadow
2X 1,2 m2 solar windows 2X60Wp61820,222 hrs morning+evening op 30% Wp,  50% shadow
2 schroef(as)dynamo 800Wp2100204,00On 5 knots 100 Watt each; upwind is zero
From: Energy Balance sheet Sustainable Yacht ‘Ya’. Remark: Here is only given the generation numbers for the scenario of 1 average day at sea. Check the Energy Balance for other scenarios

Please donot focus exclusively on the numbers. In our years of experience we learned that the essence lies in what I call the tripod of energy generation. The solar panels work together with the windmill and the hydrogeneration (prop and dynamo). If it is more cloudy, so less sunshine, then there is mostly more wind, so the windmill and/or the sailing speed makes it good. And the hydrogeneration works great downwinds, and upwind the windmill. So there is (nearly) a continuous influx.

Before building, we estimated to build in a 70 kWh of the battery bank. But in tripod-practice, we hardly need this. When sailing in the subtropics, the battery monitor balances between a 70 and 90%..

Finally, a note about failing and safety. When some generation equipment fails, we still have other ways of generation, such as the various solar panels, windmill and propellors/dynamos. This multi source fossil free sailing brings more safety and reliability than in our fossil days, when we completely had to rely on one sole source: the engine.

The Solar Panels

Next to the windmill and the dynamos/propellors (Autoprop ), the solar energy is the third way to create our energy.

Sustainable Yacht the Ya is equipped with solar panels as much as possible. We have three sorts, or sets, on board.

The ‘bimini top’ panels are the most effective, because the wind can cooltop and bottom of the thin monocrystalline cells well.

The largest area is the ‘bimini top’ panels above the cockpit,  They measure a near 4.5 m2. They are panels with the so-called monocrystalline version, because of the high yield, in our case 20% under ideal circumstances. Then they deliver 720 Wattpeek. This is under a theoretical situation, with the sun shining with a 90 degree angle on them and with a temperature of  4 degrees. A low temperature is needed for a high power; when the monocrystalline material rises in temperature, the conversion from sunlight to electricity gets less. So the biminitop panels are ideal, because they are very thin and on both sides the wind can cool the material very well. Even in the hot tropics they deliver well.

The walkable panels on deck work pretty good when the temperature is lower, like in the higher latitudes. These solar panels are designed such way that some shadow here and there is not a big issue.

The cabin deck is covered with 3,6 m2 of panels you can walk on. The panels can bend a bit and are mounted on the slightly curved cabin deck. The panels are well protected with plastic on the top. With this construction they can easily get warm, so that is at the expense of efficiency. When the outside temperature is not to warm (so summers in a temperate climate, winter in the subtropics),  they deliver around 70% compared to the panels over the cockpit per m2 surface.

Every panel has an overkill on cells, so it doesnot matter if some cells of a deck panel are covered by a shadow here and there.

The window panels are mounted where you don’t need the light. They deliver more than you think, because the sunlight at dusk and dawn also reflects on the water.

Finally, the Ya has the solar panels along the windows. They are mounted on places you don’t need the sunlight, so behind the anchor box, a cubboard, or storage box.

These panels don’t deliver that much but you can get them easy in customized sizes and they are easy to install. We glued them on plastic board and pressed them on to the inside of the windows. They don’t deliver that much, think of some 20 Watts per side, but they look swell and this is much cheaper than any other solar panel.

The alternative would be to incorporate the solar panels in the glass, but such customization becomes very expensive and that does not fit in with the Sustainable Yacht slogan: ‘Everyone sails sustainably”. One must be able to get it ‘from the shelf’, or, if customized, the price must be acceptable.

Results, numbers and practice

On a general European winter day with overcast they deliver… hardly anything. On a general European summers day they all deliver well. On a warm (sub)tropical day the deck panels get to hot to deliver well, but the thin biminitop panels make that all good.

Here under you see the rough general numbers when on a regular Transatlantic crossing from the Canaries to the Caribbean.

Generation#Watthr/daykWh/dayRemarks
4,8m2 Solar bimini 3*230Wp321663,8930% of Wp during 6 hours
3,6 m2 Solar deck 440 Wp38851,32less power due to heat and shadow
2X 1,2 m2 solar windows 2X60Wp61820,222 hrs morning+evening op 30% Wp, 50% shadow
From: Energy Balance sheet Sustainable Yacht ‘Ya’. Remark: Here is only given the generation numbers for the scenario of 1 average day at sea. Check the Energy Balance for other scenarios.

Please donot focus exclusively on the numbers. In our years of experience we learned that the essence lies in what I call the tripod of energy generation. The solar panels work together with the windmill and the hydrogeneration (prop and dynamo). If it is more cloudy, so less sunshine, then there is mostly more wind, so the windmill and/or the sailing speed makes it good. And the hydrogeneration works great downwinds, and upwind the windmill. So there is (nearly) a continuous influx.

Before building, we estimated to build in a 55 kWh of the battery bank. But in practice, we hardly need this. When sailing in the subtropics, the battery monitor balances between a 70 and 90%..

A note about failing and safety. When some generation equipment fails, we still have other ways of generation, such as other panels, windmill and propellors/dynamos. This multi source fossil free sailing brings more safety and reliability than in our fossil days, when we completely had to rely on one sole source: the engine.

The (Auto)propellors and dynamos

There are three “generators” on board the Ya: the windmill, the solar panels, and the propellors-plus-dynamos. This article tells about the dynamos and the Autoprops. It is easy to run them, and they always run when doing over 5 knots. Roughly, for 90% of our the sea time the props deliver electricity, for 9% they are not used because of no wind, and only 1% of the time we use it for propulsion.

Under the ship are two propellors, each connected to a dynamo. When sailing, the propellors give resistance and start spinning. We switch each electric engine to the dynamo function and the dynamo delivers electricity to the batteries.

Getting power from a rotating prop is not new. Traditionally this was done by transferring the power of the rotating propeller shaft to a dynamo via a pulley and V-belt. The propellor, design for high rotations for its propulsion function, doesnot work that well for this, and the transfer via the V-belt costs a lot of energy.

The “old-fashioned” method of energy generation via the screw.
The propeller shaft can be seen in the foreground. This comes through the skin on the left (invisible), and ends in the propeller in the water that will turn while sailing.
On the right we see a large pulley, with a V-belt over it, which transmits the turn and accelerates to the dynamo (the green round device on top). The faster the dynamo turns, the more electricity.

The Autoprops

The best props are large, slow running props. So the 34 foot long Ya has two 16 inch (41 cm) propellors. But for a sailing yacht the drag, the resistance of such big props would be terrible. Close hauled, this drag would lead to a seriously increasing leeway. Therefore, the Ya doesnot have fixed props, but 2 Autoprops .

This feathering position is also geat when the speed is to slow anyway to generate well (under 4,5 knots). When the Autoprops get stopped, they automatically go to the feathering position.

The Autoprop in its working mode (left) and in feathering position (right).

Also, a fixed propellor is not logical on a yacht, because it is generally designed for 1 speed. And while sailing and in generation mode, the prop will rotate slower. If one could adjust the pitch (the position of the blades), it would generate more. On a sailing yacht, also the speed will vary,. So that would require continuous adjustment, since the speed of a sailing yacht usually varies. One should adjust the pitch with every gust of wind and every wave running up and down. If the blades were continuously adjusted to the optimum position, it would be the most efficient for generation. And also for propulsion.

Well, the Autoprop arranges this adjustment automatically. When in generation mode, if the speed varies, the revolutions vary, and the blades will vary the pitch to the optimum position and vice versa. And when in propulsion mode, the blades are adjusted by the rotations and the speed through the water. This can be seen in the film below:

The Autoprop adjuists the pitch of its blades according to speed and to power. In its reverse mode it works just as efficient as in forward mode. The Autoprop therefore has the best generation efficiency, because a prop runs in reverse when it generates under sail.


Really nice for long distance sailors, is that it works on natural physics itself: the centrifugal force of the RPMs, and the speed of the boat by the impact of the water on the blades. So no electronics, no chips, wiring, nothing. Just physics. No maintenance, only some grease so now and then. Isn’t it beautiful? It helps the Ya great on its generation.

Want to know more? You find a very thorough explanation with an animation on the Bomarine site (sorry, it is Dutch spoken). The technology for the automatic adjustment is beautiful to make a tech heart running faster. But the economical hearts start running fast when you see the the various tests, where the Autoprop belongs to most efficient props. Yachting did a prop test, or check the German Segeln . Here under the outcomes of the French Voile Magazine.

The French magazine ‘Voile’ tested how many miles a yacht could make with 10 litres of diesel. The Autoprop was the best, about 1,5 times better than the most used props.

The dynamos

Beschrijving: Macintosh HD:Users:jph:Documents:Duurzaam Jacht:Media Duurzaam Jacht:Nieuwsbrief:Nieuwsbrief 5:Etech 6 motor napedyelektyczne.jpg
The E-Tech engine is also a dynamo – you simply switch the mode with a button or key.

An electric motor with a permanent magnet can easily be switched into an efficient dynamo. Technically, this type is the same as the old-fashioned bicycle dynamo. The revolutions of the current electric motor (and therefore dynamo) do not have to be very high. So you don’t need a reduction box. And a slow rotating propellor is more efficient, in generation and in propulsion. But on slow rotations, the propellor must be bigger and should be designed differently to create such good efficiency. 

With one button, each of the two 6.5 kW E-Tech engines can be switched into dynamos. These engines/dynamos have been chosen for several reasons. These motors are permanent magnet motors and perfectly suited as a dynamo. Five things were decisive for choosing E-Tech

They are brushless. Just like most marine electric motors, they no longer have brushes that “drag” along the rotor. These should be replaced frequently. This applies in particular to the Sustainable Yacht, because they will run in almost all sailing hours: as a dynamo (60-70% of the time) and as a motor (10-15% of the time).
Full liquid cooling. Not only the engine, but also the controller containing the transistors and the like is liquid cooled. Good cooling means that no power is lost to heat. This is both a gain in generation and in propulsion.
Double thrust bearing. A thrust bearing is put in between engine and propeller and absorbs the pressure the propeller emits. This prevents the propeller from exerting its force on the motor itself. A permanent pressure on the engine would causes wear, so this is prevented. Most electric motors only have a thrust bearing on the “drive side”. But on the Sustainable Yacht the engine is usually generated and the power is usually in the other direction. The propellor does not “push”, but “pulls”. The E-Tech engine is therefore equipped with a second thrust bearing.

Synchronous motor. A synchronous motor is ideally suited as a motor and as a dynamo. He can, as it were, “flow” into it.

Low maximum rotation. The maximum rotations per minute can be adjusted by the factory. On the Ya the max RPM is only 1040 RPM, with a pretty high torque (Nm). Slower rotations of the prop have three advantages: more efficiency, less noise, less wear out.
However, such a motor is more expensive to purchase, so people buy the cheaper one and then use a reduction gearbox. However, due to the gear transmissions, such a reduction means resistance, so less energy to (propulsion) and from (generation) the propellor. Another advantage of the lower revolutions is that all moving parts don’t wear out. A more durable life and a higher reliability.

The practice and the numbers

As soon as we sail more than 4 knots, we give a little reverse power to the engine, and so the Autoprop is ‘soft started’ for generation, so directly we push the Charge switch. With the throddle in neutral, we see the RPM display showing about 300. Then we push the throddle a bit to forward and the dynamo starts doing its work. Inside the cabin you can hear a light, friendly zzzzoommmm…. The dynamo gives electricity in 48 Volt DC to the batteries. This sound is not irritating at all. It gives peace of mind. A crew member once said: “Dynamo, Sweet Dynamo” 😉

On 4,5 knots the energy production is not more than some Watts. But on 5 knots the dynamo delivers 50 Watts. On 5,5 knots it nears 100 Watt and when doing 6 knots it is 120-150 Watt. Great fun it is when you reach the hull speed of the Ya of 7 knots and make 200 Watts with each dynamo.

In general, we are leisure sailors. At sea, especially the ocean, you sail  your ship conservatively and for the 34 ft Ya a general speed of 5 to 5,5 knots is good. Some people find this a high average, but realize that we have a Parasailor sail.

Perhaps you  find 100 Watts not much. Well it is much. This runs 24 hours a day, so count on a 2,5 kWh per day. This is enough to cook an extensive meal. We are happy on the Ya, because it is just enough. But it must be said that our speed is critical. I would not recommend to seriously spend money on a prop and dynamo for a leisure yacht shorter than 33 feet.

In 2012 we collected some statements from electric motor suppliers about the generation possibilities. The impression was created that with a propulsion prop, about 5% of the maximum propulsion power could be generated. That would be 650 watts with our 13 kWatt (2 times 6.5 kW) max power and therefore much much more than our practice on the Ya. But still they can be right: you only need a larger yacht! For example, a 60 ft yacht would easily do 7 or 8 knots, and then the 650 Watt generation is a piece of cake.

The Energy Balance

In the Energy Balance, we assumed values ​​that were achieved by two well-installed propeller shaft dynamos with a peak power of 800 watts. These then achieve an average of 30% of this, for 20 hours per day.

Generation#Watthr/daykWh/day
2 props+dynamos 800Wp2100204,00On 5,5 knots 100 Watt each; upwind is zero
From: Energy Balance sheet Sustainable Yacht ‘Ya’. Remark: Here is only given the generation numbers for the scenario of 1 average day at sea. Check the Energy Balance for other scenarios.

Please donot focus exclusively on the numbers. In our years of experience we learned that the essence lies in what I call the tripod of energy generation. The solar panels work together with the windmill and the hydrogeneration (prop and dynamo). If it is more cloudy, so less sunshine, then there is mostly more wind, so the windmill and/or the sailing speed makes it good. And the hydrogeneration works great downwinds, and upwind the windmill. So there is (nearly) a continuous influx.

Before building, we estimated to build in a 70 kWh of the battery bank. But in practice, we hardly need this. When sailing in the subtropics, the battery monitor balances between a 70 and 90%.

A note about failing and safety. When some generation equipment fails, we still have other ways of generation, such as other panels, windmill and propellors/dynamos. This multi source fossil free sailing brings more safety and reliability than in our fossil days, when we completely had to rely on one source: the engine.

The Heating Management (under construction)