Sun, wind and water ver 0.3

Yacht innovation

season three

A yacht is a hole in the water where you need to throw money.

(C) my friend

Now the time has come and money has appeared to carry out modernization and implement what was postponed for the future. During the operation of the yacht, the motor, selected according to the principle of minimization, showed itself quite well until we got into a storm. Well, it was predictable – he failed. At the same time, the main problems came to light:

  1. the outboard motor flies out of the water during a storm and turns the air half the time;

  2. a significant lack of power, in a storm (20 m / s) – you need to move to a safe distance and anchor;

  3. low efficiency – energy is money, and they need to be saved;

  4. poor handling when reversing;

  5. small limit of autonomy – it is necessary to increase at least up to 20-30 miles.

Using the old calculation (from the first season), I will be engaged in the selection of a normal motor, since now I have something to compare with. Initially, I considered installing an outboard motor. Primary requirements:

  • remote control module and electric starter – the feed is high and the engine cannot be reached;

  • weight – the possibility of removing the unit alone (up to 30 kg);

  • the presence of a built-in tank – I do not want to store gasoline on the yacht, and I personally have never seen gas stations in yacht clubs;

  • the presence of a generator for charging batteries;

  • “Sea leg” at least 1 meter long;

  • availability for sale.

Well, I’ll tell you right away – there is no such motor!

In terms of power, the four-stroke Mercury 9.9 is suitable.

  • power 7.3 kW (minus efficiency <0.8 of the gearbox and different piping);

  • speed 3000 rpm;

  • screw D = 13 “= 0.229 m, pitch H = 13”;

  • the maximum speed in calm weather is 4.5 knots;

  • autonomy in calm weather – by the size of the tank;

  • With a headwind of 20 m / s, it is able to give the yacht a speed of 1.4 knots with an efficiency of 10%;

  • Efficiency in normal mode (not counting the internal combustion engine) is about 50%.

Its price is more than 200 thousand, plus a remote control module and an external gas tank and a new suspension. Everything depreciates the length of the “leg” of 0.5 m. In this case, it will simply not be possible to use it in a storm – the leg will jump out of the water and the motor will overheat. There is one more problem. The propeller will be located just behind the rudder and the handling of such a vessel will be very poor.

The only solution seems to me to use a stationary motor located under the bottom of the yacht.

Even the first attempts at selection indicated a cost comparable to that of the yacht itself. In addition, the motor should take a place in the very center of the yacht, thus stealing 2 of the 3 berths in the aft cabin. The installation of such a motor is associated with a serious decrease in the strength of the keel bar – this is the main ridge of the ship’s strength. Such work must be done at the shipyard, which is also not free.

The problem of propeller protection from underwater obstacles is becoming acute. On a two-keel yacht, the keels form a kind of protected tunnel – it is there, logically, that it is best to install the propeller.

This means that the Z-gear and the shaft will take place in the central aisle of the wardroom.

A solution devoid of all the shortcomings was found. Having already had some experience in operating an electric motor on a yacht, I drew attention to a relatively new class of devices – stationary electric yacht motors, the so-called pod-drive. In Russia, they are not represented at all. And in the world of real experience of use, judging by the Internet, there is very little. The only brand I could reach from Russia was Torqeedo.

It seems that these devices are free from all the disadvantages described above. The motor itself does not take up space on board the yacht and is completely located under water. This, by the way, solves the issue with its cooling.

The efficiency of a synchronous electric motor with a PWM drive is usually slightly different from 100%. And the presence of a folding screw makes it just a gift for the yacht. Well, let’s see how the advertising corresponds to reality.

For such a motor, it makes sense to provide new batteries. There is enough space under the floorboards, but the dimensions allow you to set a standard size of no more than 120 A * h – I will take 4 pieces.

In my class of yachts, with a displacement of up to 2.5 tons, the manufacturer offers two motors CRUISE 2 FP – up to 3 tons and CRUISE 4 FP – up to 10 tons. It would seem that the choice is obvious – the smaller one suits me. 🙂 I almost didn’t believe in advertising!

To obtain the information necessary for the calculation, I contacted the manufacturer’s technical support and received the parameters of the propeller, pitch = 0.229 m and diameter = 0.33 m. These data are not in the documentation.

Now let’s compare advertising statements with calculations, fortunately, I already have a proven calculation.

I’ll start with the CRUISE 2 FP motor recommended by the manufacturer.

  • power 2 kW;

  • revolutions 1300 rpm;

  • screw D = 0.33 m, pitch H = 13 ”;

  • the maximum speed in calm weather is 4.5 knots;

  • autonomy in calm weather at a vessel speed of 3 knots – 25 miles;

  • With a headwind of 14 m / s, it is able to give the yacht a speed of more than 1 knot with an efficiency of 10%;

  • The efficiency in normal mode is about 50%, but after 3.6 knots, the efficiency begins to fall due to the slip of the screw.

Well, let’s just say, it does not even reach the mercury 5 sail in all characteristics – rather weak!

Let’s see what the CRUISE 4 FP is capable of.

  • power 4 kW;

  • revolutions 1300 rpm;

  • screw D = 0.33 m, pitch H = 13 ”;

  • the maximum speed in calm weather is 4.5 knots;

  • autonomy in calm weather at a vessel speed of 3 knots – 30 miles;

  • With a headwind of 20 m / s, it is able to give the yacht a speed of more than 1 knot with an efficiency of 10%;

  • Efficiency in normal mode is more than 52%.

Now that’s a completely different matter! Such a kit turned out to be a little more expensive than a 9.9 gasoline suspension bracket, but it fits into the budget. I take it!

The first problem is the transition of the on-board network from 12 to 48 V. For the instruments and lights of the yacht, a dc / dc 48-12 converter for 20-50 W is needed. Well, here is aliexpress to help. Another thing is with solar panels. There is not much space on board and I have already occupied it with suitable batteries. Their operating voltage is 19.5 V and even two together they will not provide a 48 V battery charge. In addition, the energy intensity of the batteries has grown significantly. There were no standard solutions for 48V, so we will do it on our own. How lucky my daughter has a course project. I throw in the topic: “Solar panel controller”.


  • the maximum possible battery utilization rate, let me remind you that the current solar installation has an efficiency of <10%;

  • battery charge 48 V;

  • the ability to connect other energy sources: solar panels, wind turbines, batteries, gas generators – as an expansion option.

More on this in her article. I’ll focus on the motor and batteries.

What batteries to take? The first answer that comes to mind is of course lithium iron! Lightweight, compact and insanely expensive! What about AGM?

The engine in nominal mode consumes only 12 A at 48 V. If we take an AGM for 120 A * h, then this is only 0.1 C! According to the discharge characteristic, this corresponds to 9 hours of discharge – 90% of the capacity is available. With an average summer temperature above 30 degrees, 100% capacity is available.

The result is similar to that of lithium iron, only 4 times cheaper.

Peak current of 80A is possible only in storm mode. Here the charge is enough for less than an hour to move away, hide and anchor. For the future, I am seriously thinking about a small gas generator for very emergencies. Time will show. But so far the practice is such that it is better to stand and wait in a storm.

So, decided, put 4 pieces of delta dt-12120. Since the batteries are installed below the waterline, the boat, in addition, will gain even better stability.

Choosing a place to install the motor.

First you need to decide on the best travel speeds. Every self-respecting physicist knows that our world is discrete. Everything that moves and vibrates is quantized. A boat moving through the water creates a wave. The length and amplitude of the wave depends on the speed of movement.   lambda = 2 *  pi * v ^ 2 / 9.8

The maximum of this wave falls on the nose. The water in the wave moves in the direction from the maximum to the minimum. If there is a growing section of the wave at the stern of the boat, then the water moves in its direction.

This is called “feed draws water”. Part of the energy is spent on this, and the boat experiences additional resistance to movement. When the wave falls at the stern, then everything happens the other way around, and the resistance falls.

Thus, as the speed increases, the boat seems to jump over the resistance maxima, trying to stay in the minimums (in potential holes).

On the other hand, the motor is essentially a pump that creates a vacuum in front and a high pressure zone behind it.

Water tends to return back from high pressure to low pressure and forms parasitic flows. This reduces the efficiency of the propeller.

To reduce this “parasitism”, it is necessary to place the propeller so that the wave decay falls on both the propeller and the stern, as if removing excess water pressure. With an outboard motor, this happens automatically, but with a stationary motor, it is more complicated.

The wave distribution at the most popular sailing speed of 3 knots shows that setting the propeller in front of the rudder blade is the most undesirable location (marked NS). The star denotes the most successful place in terms of the efficiency of the entire system.

Installing the propeller in this place will slightly worsen the boat’s controllability at very low speeds when moving forward under the engine, because the jet from the propeller will not reach the rudder blade. But it will improve maneuverability when reversing, because the leverage will be significant.

The most successful speeds for this yacht are: 3.15 – 3.64 – 4.46 – 6.3 knots. This corresponds to the series  n *  lambda + 0.25 = lvlwhere n is an integer; lвл – the length of the waterline. vхор =  sqrt {9,8 * (lвл-0,25) / (2 *  pi * n)}

And the most unsuccessful – a number of speeds: 3.27 – 3.77 – 4.62 – 6.53 knots. The degree of influence of the elements of the rows increases with the increase in the speed of the vessel. A speed of 6.3 is unattainable under a motor and it is obvious that the maximum wave drag at a speed of 4.62 knots limits the maximum speed of all considered motors. At the same time, an acceptable autonomy of 30 miles is achieved at a speed of just under 3 knots. And numbers from a number of successful speeds are related as 3.15 * 2 = 4.46. This suggests that the wavelengths of these elements of the series will differ by a factor of two. Consequently, the decline will begin at one point, and the optimal section for installing the motor will also begin at the same point – 3.32 meters from the beginning of the waterline.

Similarly, I consider the place for the most unfortunate location of the motor – this will correspond to speeds of 3.27 and 4.62 knots. The most unfortunate section of the motor installation will begin at 3.57 meters from the beginning of the waterline.

Conclusion: the most favorable location for the propeller in terms of energy saving and increasing the efficiency of the system will be in the range from 3.32 to 3.57 meters from the beginning of the waterline.

Great result! The motor will be located between the keels and will be protected from poaching nets, of which we have plenty.

Now a little about German surprises.

The motor comes with power wires, an engine control unit, cables and a gps antenna. But here’s what I did not expect from pedantic Germans – a power switch for a voltage of 32 V for switching a 48 V circuit.

A couple more surprises:

Firstly, the safety key is made on the basis of such a strong magnet that having one on a yacht you can easily open America instead of India. The compass reacts to it at a distance of a meter!

Secondly, the control module itself is not much better. A strong magnet is also built into the engine control handle so that when you move the throttle handle, the compass rotates 180 degrees! What are the Germans thinking now?

These surprises are still waiting for their engineering solution. After all, it is logical that the control module should be placed on the steering column in close proximity to the compass.


Of course, solutions were found and the engine proved to be excellent. Calculations are confirmed in real trips. The autonomy limit has so far been checked only by the readings of the motor controller – it is 40 miles at a speed of up to 3 knots and 95 miles in motor-sail mode (sail with a motor).

During the operation, problems were also discovered. First, the keels do not really protect the propeller from the nets. With a lateral longitudinal approach, the net winds up perfectly, but cutting it off under the keels is a quest! Secondly, in the instructions for the engine, the Germans wrote: do not cover with antifouling coatings …

this is how the engine looks after the first season
this is how the engine looks after the first season

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