Electric final drive

I guess your service as submariner explain why you re interested in electric propulsion

It s been tried but it's either more expensive than diesel when done right or if it's cheaper well it's cheaper.

I built a 26' classic day sailor and used an inboard electric motor with a convential shaft powered by 8 golf cart batteries. I just upgraded the motor to a water cooled unit and the original open frame motor had corrosion issues in the salt environment.

The problem I see with electric propulsion in larger sailboat is that you ll likely still need a diesel generator anyway so I'm not sure there are any real benefits to going electric

Do you have the room in a 44 ft sailboat to store 10,000lbs of batteries without having an adverse effect on the vessel?

Batteries as ballast won't work on most sailboats as it will not be low enough to be as effective as a keel. A battery also has water and air in it reducing the mass per volume ratio

And even if you could, like in a classic full keel hull, you d have a problem with the batteries getting wet unless you have a way to fully seal the bilge above

Lead weighs ~700 lbs per cubic foot, lead acid batteries weigh ~100-150 lbs per cubic foot. On top of that they are inconveniently shaped to be poured into a keel. In lead acid that equates to something like 150 kWh if you are willing to run them down all the way. Other batteries will do a lot more for you, but cost more and have higher bulk to mass ratios (lower density) which is cool if you've got a lot of room but less so on a cramped sailboat.

Diesel electric is a better choice perhaps for a sailboat that doesn't have a nuclear reactor but does have constant access to combustable air. Diesel electric allows you to tuck your diesel engine where it is least inconvenient for you and route heavy copper cables down to the drive instead of letting shaft alignment dictate where you put your iron topsail.

Unfortunately the electric motor itself is going to have some bulk to it, so if you get a unit that it outside of the boat in a pod (saving yourself the difficulty of working with fragile shaft seals) you pay the penalty in extra drag while you are using the boat for its intended purpose (sailing).

Yeah but the shaft seals in an convential drive rarely fail and can be maintained. In a pod you won't know they've failed till it's too late, don't you? And then you have to haul out

I don't know if there are any large enough for his application but there are electric drives and thrusters that don't have any kind of seal on any moving part. If you pot all the electrical components in epoxy water getting in between the field windings and a permanent magnet or potted induction rotor doesn't actually do anything.

That said I was thinking more about the fiddly work involved in installation than the rare failure. An electrical unit bolted onto the hull is a lot more forgiving of a few milimeters worth of mistake than a prop shaft is.

Both configurations have their advantages and disadvantages.

Not to mention, do you know what 10,000 lbs of batteries would cost every 3 years to replace? A diesel inboard sailboat is pretty darn cheap to operate when it comes to fuel...... Besides, you're supposed to be using the wind anyways!!!!!!!!!!!!!!

Since that 10k pounds of ballast already exists in a form and location that works very well, any attempt to relocate it higher and distribute it around the water plane will likely create more problems than benefits.

With regard to converting a very small recreational sailboat to electrical propulsion, it is difficult to justify the added complexity, reduced reliability, and increased costs for so little (if any) operational benefit. It is a tinkerer's dream though and would be lots of fun but that is about the extent of how it might be justified.

I don't agree about the complexity of an electric drive on smaller boat, say under 40/45'. If anything it s pretty simple. A motor, a controler, a charger and batteries. No oil change, no fuel system to maintain, no fuel getting stale.

And you're not going to have or need 10 000 lbs of batteries, after all, motors on sailboat are called auxiliary for a reason.

And batteries last a little longer than 3 years.

Is it for everyone, no... but in smaller boats there are many benefits starting with the fact that fitting a diesel can be extremely challenging due to space. I know that there was no way to fit anything but an electric on my 26 footer with centerboard. Yes an outboard could have worked but they're ugly, always in the way and just as expensive. After two years of use, I m happy with my decision

There are a number of turn key kits on the market ready to install that you don't have to tinker with.

It again, it depends on your needs but general statements like posted above are not accurate.

I guess if one is interested in having a 44 foot deep draft equivalent of a Duffy then replacing the diesel auxiliary with batteries, controls, and a motor would be interesting but given that most sailboats that size probably spend as much or more time motoring than sailing it wouldn't add much utility. Without some means of onboard charging or more batteries than the boat could float or anyone would care to live with, motoring time (especially against any kind of wind or seas) might be extremely limited. This takes you back to hybrid diesel electric along with its cost and complexity. As anything but a hobby or recreational experiment what's the benefit? If the novelty of having an electric sailboat or modifying one as a learning exercise is the objective then it would be a fun way to spend spare time and money.