Electric motors boast many advantages over diesel motors. They are quiet, clean, and virtually maintenance free! They run when you need them to and stand idly by when you don't. When sailing along with speed, the spinning propeller actually generates electricity for you to recharge your battery banks.
The one advantage that a diesel motor has over an electric is range. There is nothing quit as energy dense as fossil fuel on a yacht. A small volume of liquid will power your yacht for hours and miles without a single complaint. If you run low on this magical wonder juice, all you need to do is pull up to a fuel dock and pour some more into your fuel tank! This is a quick process that takes only minutes to complete.
Electric motors carry their energy source inside of batteries which will gladly give up their power, but seem to resist accepting power in return. When a fuel tank is empty, all you need to do is pour more fuel in! When a battery is empty, you will need to force power back into it with considerable effort, a process that can take many hours to complete.
If you plan on motoring fast and far for long periods of time, a fossil fuel motor would be your best choice. If you plan on using your motor for short spurts of power, followed by days of sailing, an electric motor might be a better fit for you.
Electricity stored in batteries is odorless and clean. It doesn't need to be run through filters or polishers to keep it clean, instead it simply sits waiting for you to call on it.
Now, what if you find that an electric motor would be your dream power source in your yacht, but you do plan on the occasional motoring. You could solve this dilemma with a simple compromise. A generator will grant you the ease of fossil fuels and the convenience of electric propulsion. The generator powers your battery charger which feeds the battery bank and motor.
Now, your range and speed will be decided based on your charging capabilities. Your generator will only provide as much power as the charger can put out. If you have a 5 amp charger, then you will only be able to motor along at 5 amps with the range of your fuel supply. If you are wondering, 5 amps is hardly moving and you might be better off to just drift with the tide!
If you have more charging capability, say 25 amps, you would then be able to motor along at 25 amps (which is still slow, but you would be moving at around 3 knots) for as long as your fuel supply lasts.
As you can see, the more charging you can produce, the more speed you can motor with. While you may feel limited by your charger, this should not be a concern.
For example, say you have 15 amps of charging capability, which will motor you along at around 2 knots. You want to go 5 knots and are drawing 60 amps, you can simply throttle up to 60 amps and know that you are drawing 15 amps from the charger and 45 amps from the batteries. This will let you motor along for a few hours at this speed before you will need to slow down and run at a speed governed by the generator and charger.
This might seem like it is limiting, but if you need to motor 20 miles, 5 knots will get you there in 4 hours. Once you are there, you can let the generator continue to run and recharge the battery banks once you have arrived with speed and ease.
Generators give you a portable charging solution, adding greatly extended range to your electric propulsion setup. When coupled with solar panels as well, you will find that you will be able to motor along well enough to grant you the peace and tranquility you wanted every time you need that short burst of power.