It is generally accepted that a hybrid installation is excessively heavy for a sailboat. Let's calculate in real numbers what exactly and how much it weighs.

I’ll definetely confirm that a hybrid engine cannot be lighter than a classic ICE one, this is obvious.

To begin with, let's look at a real example - my boat, I have some ideas on how to lighten weight, but I will consider it after I try it in real life.

The power of the electric motor and generator is sufficient to go into 30 knots wind at a speed of 5 km/h as long as there is gasoline. Consumption in this mode is 1 liter of gasoline per hour of operation.

If weather conditions are more favorable, fuel consumption will be lower. If you sail in calm, you will practically do not need to run the generator.

So, the weight of the components of my engine:

  1. Battery - 40 kg
  2. Engine - 15 kg
  3. Controller - 2 kg
  4. Generator with air cooling pipes, with a water lock and a pump for supplying water to the exhaust pipe and water lock - 25 kg

The total weight with the generator is 82 kg. Without generator - 57 kg.

And now let's remember that on ordinary boats there is a heavy lead service battery weight a 15-40 kg. If we take into account that it is better not to discharge lead batteries by more than half for their long life, then the energy reserve in them is extremely small: from 12V ⋅ 60Ah / 2 = 360Wh and up to 12V ⋅ 150Ah / 2 = 900 Wh (maybe more than 150 Ah, but then the weight will be more than 40 kg). For comparison - the energy reserve in the battery of the engine of my boat is 6000 Wh with its weight 40 kg.

What is 6000 Wh? How much energy is this in the usual sense? A few examples of how much this energy is enough for domestic use:

  • Electric kettle for 3-4 hours boiling without interruptions
  • Drills/grinders for 6 hours without breaks
  • Microwave for 6 hours of heating without interruption
  • 15 hours of air heating at 5 degrees overboard and 20 degrees inside a boat of my size (approximately 8 meters long)
  • Heating in an electric boiler 100-120 liters of water from a temperature of 20 degrees to a temperature of 60 degrees

Given that the engine battery has a substantial supply of energy, it is convenient to power the on-board electronics from the voltage converter from the engine battery to 12V. So, the hybrid allows weight saving from 15 to 40 kg, which means the total installation weight: from 42 kg to 67 kg together with the generator. Not so much, right?

I believe that it is necessary to carry onboard one 12V lithium battery that is not connected to the boat network, with a relatively small capacity - 100Ah just in case. Self-discharge of lithium is extremely small - in the region of 2% per month. At the same time, winter storage is possible without consequences if you do not charge it at low temperatures. Such lithium battery, just in case, will weight about 12 kg.

Where is the weight of the hybrid unit in the boat?

The heaviest component - the battery - is located next to the keel.

Electric motor with controller located further in the stern, under the deck in the area of the sailboat cabin door. These components will require your attention after 10 years for repair or replacement. Therefore, it is safe to place the electric motor so that its compartment takes up a minimum of space.

Generator located under the cockpit, access to it through the hatch in the cockpit deck.

No one bothers to place the battery and generator anywhere in the boat. However, the generator requires maintenance, so it must be located in a place where it is convenient to get to it. The battery can be located in any inaccessible place, as you will need to pull out or maintain it rarely - one time in 5-8 years.