Electric motor manufacturers state many advantages over diesels.
They have less moving parts to break
They don't smell
They don't pollute
They are smaller
They don't use fuel
They are quieter
These things are all true, but I don't think they get the point across of just how different they are from diesel engines.
I used to fix my diesel engine every time it died, which was almost every time I went sailing. I spent plenty of time bleeding the injectors, adjusting the valves, changing impellers and filters, and clearing debris from the strainers. It usually died when I was docking and would throw it in reverse to slow me down as I came into my slip. I was so fed up with the diesel that I decided to pull it out and be completely engineless. Maddie quickly asked:
"If we were sailing along and came across a marina in unfavorable conditions, how would we dock?"
My answer of "we don't" was not well received. For this reason, we decided on an electric motor to get us in and out of marinas. While we chose a very small battery bank, just enough to get us in and out of marinas, a properly sized battery bank would allow for a much longer motoring range. If you combine a larger battery bank with a generator, you can extend your range even further yet! But we prefer to sail, so we went with as small of a battery bank as we could.
The more parts involved, the more parts available to fail, and the more times the diesel won't work perfectly. This combined with the fact that sailboats mistreat their diesels in horrible ways. Diesels are meant to be turned on, warmed up and then run under a load for hours before being shut down. Sailboats turn them on to leave the marina (not much load or run time) and then shut them down. Then the occasional start up to get out of the way of a cargo ship or to charge the batteries, neither of them offer the run time nor the load a diesel needs to survive.
They have less moving parts to break
Electric motors have a 1 moving part, the output shaft. Electric motors are made up of three main parts, a Rotor (output shaft) which is permanently attached to a Stator, so they move as one piece. The last main component of the motor is the Windings, which also do not move. There are no parts that burn, grind, or wear out like a diesel motor has. They work because of physics! Electro-magnetism will always make the rotor spin without any parts actually touching each other. The motor works because an electric field is applied to the windings which causes the stator and rotor assembly to spin, which spins the propeller. There is no transmission, or fuel pump, or injectors to complicate the system, it simply works when you need it on demand!
When the diesel would fail to run, I would have to figure out what the problem was this time. When the electric would fail to run, it was because I forgot to turn it on.
From a smell stand point, electric motors are worlds apart. If you have a diesel engine and want to know what it would smell like with an electric motor, all you have to do is anchor out in a quiet creek, far removed from civilization where the birds are flying around in the calm fresh breeze. Take a good sniff, that is what it could smell like inside your cabin!
Diesel motors pollute, and there is no nice way around it. As many filters and systems (which complicate the motor) that they add, you still can't stand next to a running diesel engine in a closed room. The exhaust will make you feel ill in a few minutes and then kill you shortly after that. It is perfectly safe to be in a closed room with a running electric motor.
When you picture the serenity of a sailboat gliding through the water, you don't associate it with the large black plume of exhaust smoke that accompanies a diesel engine.
Please start video at 1:25
Electric motors don't have an exhaust pipe, because they don't have any toxic exhaust that needs to be shunted outside. The simply spin along quietly in their little space, quietly turning the propeller.
On the note of space, the size difference is insane! My old diesel motor weighed over 700lbs and produced 30hp at full throttle. It also occupied the entire space under the galley, nav station, and companionway. The electric fits in the space of the old transmission and weighs only 135lbs, producing 27hp (20kW).
Electric motors do not consume fossil fuels. I have talked with other cruisers about budgeting and average expenditures while cruising. They all have a rather large portion that gets burned up in fuel. One couple said they use around $400 a month in fuel, another solo sailor uses $750 a month in fuel! When we did our trip for a month, we never even thought about fuel costs. We budgeted for food and excursions in the places we sailed to. The three marinas we stopped in let us plug in to recharge our batteries, costing us $4 in electric per day. This electric also ran our fridge and air conditioner, but the total cost for our electric hook ups in the month ran $24. While under sail, the propeller would spin and recharge the battery bank (regeneration). When we sailed at 7 knots, we were able to produce 200W! Comparing our month to those cruisers, we had an extra $400 to $750 a month for excursions and on-shore dinners.
The best part of an electric motor is the silence! When you are in neutral, the propeller isn't spinning and neither is the motor; resulting in complete silence. When you are in forward or reverse, the motor is turning silently and the propeller slices through the water. When you apply a lot of throttle, the propeller will begin to cavitate and make propeller noise. The first time I put the boat in full speed ahead, I heard the prop noise and was startled. I never heard my own prop noise because of the loud clunking diesel. For the sake of silence, I try to keep prop speed down to just below cavitation speed, that way the motor makes no noise and neither does the propeller.
The biggest difference in the quality of boating offered by the electric motor is the peace on board when you need mechanical propulsion. We liveaboard with our parrot (Sammy) and our dog (Morty). Sammy would scream and screech with terror whenever the diesel would be turned on. There was no sound insulation, so the floors would rattle as the large clunker banged away underfoot. The floor boards would become hot, and it would hurt your ears to be in the cabin with the engine running. Morty would panic and start barking at the noise, running around trying to find the source of this noise! This horrible noise is what made me the sailor I am. I hated running the motor and refused to run it any more than necessary. I loved the peace so much and couldn't bring myself to crank on the noisy smelly monster. I would sail in and out of every creek and river on the bay. When there was no wind, I would rather sit than listen to the diesel. If I did have to motor any great distance, I would bring my parrot and dog into the cockpit and close up the cabin to try and keep the noise down to a tolerable level. It was such a hassle which is what made the electric motor seem like such a blessing.
It runs quietly, smoothly, and with no smoke or screaming pets. When we have needed to motor, Sammy the parrot is content in her cage in the salon, and Morty the dog continues to sleep peacefully.
If we get caught in irons, we can give the motor a boost of throttle to get us through the tack. When a cargo ship sneaks up on us, we can quickly power out of his way. We can easily flip a switch to turn the engine on, give it throttle, and then turn it right off without any worry about hurting the diesel.
If you are thinking of going engineless, do consider a small electric motor. They can prove to be a very handy tool while out sailing. They can provide the mechanical propulsion needed in an instant when getting an oar set up or getting a pushboat ready is not feasible without all the negatives associated with a motor while cruising.