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Old 18-08-2015, 09:56   #1
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Talking Electric Inboard

The hubs and I are looking to begin our live aboard adventure! We're really interested in an electric motor verses the diesel. I have a few questions
1- anyone switch out the two? Was it a big deal?
2- so there's no wind/ sun for charging the batteries, do you have to have a generator on board or is there another secret way to get power

I guess that's it for now... or maybe someone can direct me to a forum/ feed that is discussing this.

Thank you!
Stephanie
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Old 18-08-2015, 10:13   #2
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Re: Electric Inboard

There have been many discussions about electric sailboat power. They all come down to "how will the sailboat be used?" Starting at post #28 in the following thread I lay out a lot of details about the issues and costs associated with using electric power in a long distance cruising boat - Lots of details and numbers!

Elon Musk's New System -- Good for Boats?

My posts at #28, #73 and #75 layout the financial, weight, and practical problems associated with electric motivation on a long distance sailboat.
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Old 18-08-2015, 14:04   #3
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Re: Electric Inboard

As a live aboard they really aren't practical. Possible yes, but not realistic. There is absolutely nothing wrong with the engines, it all comes down to energy storage (i.e. batteries can't store enough) and energy production (solar and wind can't generate enough) for propulsion.

Just the quick numbers...

For every pound of diesel (7.5 lbs/gallon) you need 50 lbs of batteries. So a 10 gallon diesel tank would need to be replaced with about 3,750 lbs of batteries for the same propulsive effect.

The same number work for power generation. If you use 10hp to motor at a given speed you use 7.4kw/hr of power. Motor for 8 hours and you need to generate 59 kwh of power. Assuming a 300 watt panel at 100% rated production/day will generate 1.8 kwh/day. It would take a month to recharge the batteries (ignoring charging inefficiency). Of course you could add more panels to reduce this... but somewhere around 3-4 panels on a 40' boat seems to be the practical limit. So assuming you use no other electrical power and had four panels it will take you 8 days or so to recharge the batteries.

These numbers btw are assuming grossly in favor of electrical propulsion, realistically production will be far short of this. And most people will be using a good part of what PV panels generate to cover house loads like lights and refrigeration.

The obvious answer here is that you could install a large diesel generator to power the electric engine when its needed. And there are some boats headed in this direction. Generally it requires a small battery bank, but the cost numbers aren't really in its favor either. Though more so than pure electric.
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Old 18-08-2015, 14:18   #4
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Re: Electric Inboard

What problem are you trying to solve by going electric?

As others have pointed out, they come with major disadvantages.

If you are thinking a generator with the electric motor will be like a hybrid car, that fails to provide the same benefits. Car engines are sized based on acceleration requirements. Since electric motors put out maximum torque at pretty much any speed, you can get away with a small electric motor in a car (just big enough to maintain freeway speeds). A gas engine needs to be bigger because at low RPM, the engine is putting out much less than it's rated power. In a cruising boat, acceleration from 0-6kts isn't important, so the engines are sized based on crusing speed desired. The result is the diesel is typically running at it's most efficent speed as you get up to speed and leave it there, often for hours at a time.
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Old 18-08-2015, 14:23   #5
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Re: Electric Inboard

Hi Stephanie and welcome to the forum.

Electric is a very common question on this forum. Tacomasailor already pointed you to one thread. With the forum search function you can find many more.

Stumble already pointed out a couple of the problems with electric but let me add my own summary.

- If you buy an off the shelf "marine" electric propulsion system they tend to be expensive.
- No there is no free lunch, no secret source of power. You have to charge the batteries that run the electric motor someway; generator, solar, wind, etc.
- Unless you have a generator and/or a couple thousand pounds of batteries you will be limited to just a few miles range under power, maybe 10-30 miles max in most boats. Solar, wind, etc just don't make enough power to keep the motor running. So bottom line, most people with electric use it to get in and out of the marina and sail from there.

I wish it was otherwise. If it was more practical I would love to go electric but for most cruisers it isn't the right answer.

By the way, I'm just up the road in Gainesville and have my fixer upper boat parked in the woods just outside Alachua. You and the hubby are welcome to come by, look at the boat and listen to me tell lies and pontificate about boating and cruising.
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Old 18-08-2015, 14:58   #6
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Re: Electric Inboard

G'day Stephanie,

Welcome aboard!

The standard forum search function is a little pedestrian, better results are gained from the google search or an external search engine targeted on the forum root Cruisers & Sailing Forums - Powered by vBulletin

Diesel-electric is certainly appealing...I've taken the liberty of adding a few threads where the subject has already been kicked about, there are more, and several very knowledgable folks that are using d-e:

Electrical Propulsion vs Diesel Propulsion

Conversion to Electric Motor

Diesel Electric Propulsion

Electric Propulsion

parallel hybrid for propulsion

It Begins: Converting Cal 2-27 to Electric Propulsion!

Upgrading My Electric Propulsion System

Electric Sailboat . . . On The Cheap ?

Range using electric propulsion

.................................................. .................................................. ....
The advantages that appeal to me are:

high torque for maneuvering at low speeds

diesel generator running at optimum efficiency

small battery bank for instant on-demand maneuvering

solar panels for recharging and solar-electric sailing

more flexibility in locating generator

power-takeoff on the diesel motor for a decent compressor, and a honking great trash pump

off-the-shelf industrial diesel, a rugged Hatz 1D90 putting out 11.2 kW @ 3000rpm, 108kg dry weight, continuous tilt up to 25 degrees

air-cooled diesel, no through-hulls
.................................................. .................................................. ....

All the best!
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Old 19-08-2015, 04:30   #7
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Re: Electric Inboard

Greetings and welcome aboard the CF, Stephanie.
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Old 19-08-2015, 05:29   #8
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Re: Electric Inboard

Quote:
Originally Posted by micah719 View Post
G'day
.................................................. .................................................. ....
The advantages that appeal to me are:

high torque for maneuvering at low speeds Not critical as there is time for the engine to spool up. Lots of power when maneuvering usually winds up with mistakes. Watch a big power boat some time when they get throttle happy. They usually overcorrect and hit something.

diesel generator running at optimum efficiency Standard diesel drivetrains already run at optimal efficiency. When you account for efficiency losses converting mechanical energy to electrical and then back to mechanical, a standard diesel is typically more efficient.

small battery bank for instant on-demand maneuvering Not clear what this means. When I put it in gear, the engine gives me on-demand maneuvering. I usually leave the keys in the ignition at anchor, so if you are thinking about a dragging anchor situation, it takes 2 seconds to have the engine running.

solar panels for recharging and solar-electric sailing As stated previously by others, the solar array needed to get any significant range would be insanely large.

more flexibility in locating generator True but only if designing a boat from scratch. Retrofitting usually leaves the engine in the same place as it's the only available space big enough and outfitted to accept an engine.

power-takeoff on the diesel motor for a decent compressor, and a honking great trash pump I'll give you the compressor but a mechanical trash pump will likely beat out an electric one. Reality is most boats don't have one, nor is it high on the priority list.

off-the-shelf industrial diesel, a rugged Hatz 1D90 putting out 11.2 kW @ 3000rpm, 108kg dry weight, continuous tilt up to 25 degrees That's rather small for anything larger than a 25' boat. Remember, it's the cruising speed that determines HP requirements. If you replace the specified 40hp diesel with a 10hp electric, your performance will suffer. If you are willing to live with that inferior performance, you could just as easily drop to a 10hp diesel and achieve the same effect. Also, I wouldn't want an odd ball motor that no one is familiar with. Local marine mechanics likely won't be stocking parts for it.

air-cooled diesel, no through-hulls. While I love the idea of no thru hulls, if that is a priority, you can get a boat with a dry stack and standard diesel drivetrain. Dry stack exhaust comes with it's own hassles. Mostly needing space for it. Diesel-electric really doesn't provide any advantage here.
.................................................. .................................................. ....

All the best!
The one item I will give is if you want to anchor out and run the air-con regularly, it does mean you won't need a separate generator. The downside is it will probably be way oversized and inefficient for house electrical needs, so if you do it a lot, you lose the efficiency. If you rarely do it, it's not a big benefit.
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Old 19-08-2015, 05:45   #9
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Re: Electric Inboard

Stephanie, if your heart is set on electric, you might want to consider a hybrid or a deisel electric along the lines of a Toyota Prius.

As mentioned above, energy storage isn't advanced enough yet for pure electric, which can be a major safety concern, running out of juice in dirty weather close to shore can be kind of bad.



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Old 19-08-2015, 08:37   #10
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Re: Electric Inboard

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Originally Posted by valhalla360 View Post
The one item I will give is if you want to anchor out and run the air-con regularly, it does mean you won't need a separate generator. The downside is it will probably be way oversized and inefficient for house electrical needs, so if you do it a lot, you lose the efficiency. If you rarely do it, it's not a big benefit.
Thanks for the detailed reply. I won't have aircon; most of the world gets by without it, and the cost isn't worth it for me. Besides, I'll visit boats and buildings that do have it...



Instant on-demand power for maneuvering; By simply flicking a switch I have power at the prop. No starting, no warmup, no danger of cruddy fuel clogging injectors in lumpy seas (eg bar crossing) just when I need the motor most.

Diesels have a rev-range where they are happiest. How that gets transmitted to the water is another kind of beast. If it were that inefficient, there wouldn't be so many large d-e systems. It is only in its infancy on small private boats.

Solar sailing is a little like motor sailing, only silent and cheap; propulsion wise there isn't much thrust, but it does supply enough to cancel out the drag of a prop, and anything more contributes to canceling out hull drag and begins increasing the apparent wind. Since the battery bank is relatively small for a d-e installation, it charges relatively quickly without having acres of silicon.

The trash pump is backup for the bilge pumps and the shaft pump on the propulsion motor. Multiple ways to get the water out...a good thing! It also protects the motor itself, because if things get that sporty, it will be vital to keep it running. There will be enough flotation to spare to keep the boat afloat, and I'd rather have as much self-sufficiency as possible. This isn't a coastal cruiser and I'm not including any outside help as anything but a bonus. Who knows, off the beaten track I might be the rescuer with this kind of gear.

High torque at low speed; diesels don't like low speed. I'm talking less than idling speed, 800rpm or less. Getting a consistent quarter or half knot is more controllable than having to blip the throttle on a diesel. Also, it's silent, which the anchorage neighbours will appreciate.

The electric drive motor will be around 7.5kW. Plenty enough for this size boat. It's 50/50 whether I go with a motor at all but if I do, this is how it will be. It is a new build, so I can place the heavy things where they are best integrated into the whole. 40hp is way too much for 26 feet and about 5.5 tons. 20 is more like it.

No through hulls and no engine plumbing greatly simplifies the system. The penalty is as you say in space, but since I can put the motor where I want, I can also choose the best way to supply cooling and combustion air, in such as way as to minimise the risk of taking in water, either flooding or corrosion. Bilge pump drain goes into the cockpit, and if I want raw salt water for washing I'll live with the inconvenience of pumping it into a temporary holding tank from a hose through the cockpit drain...I wouldn't hold on to it more than a day, it'll stink. With 0 through-hulls there is that much less chance of sinking. The air intakes and exhaust are in a spot that, if it is getting green water, I won't be running the diesel anyway, and will likely have other problems...at 140 degrees list. The battery electric will still run, though....
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Old 19-08-2015, 08:51   #11
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Re: Electric Inboard

there is an electric drive formosa 41 in barra de naviidad for sale..
does excellent job off maneuvering and sailing.
ye might wanna consult pitt bolinate, on facebook about this.. he has been cruising his for many thousands of miles, now.
there was also a 35 or 36 ft sloop came thru here 2 yrs ago with an inboard well sporting a torqueedo t1003s.... they said it did an excellent job of propelling boat. they also used the motor on their dinghy.
y'all do realize that these are SAILboats and the owners DO sail as well as use motor for times deemed necessary
addvantage, not even neeeding to be said--immediate start up in emergencies-- whereas diesel makes complaints and doesnt start right NOWdammit....
silence while operating yet continues to make way.....
what's not to like...
remember, it isnot the motor nor engine that maneuvers the boat, but the loose nut behind the wheel/at the tiller....
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Old 19-08-2015, 09:38   #12
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Re: Electric Inboard

[QUOTE=micah719;1894526]Thanks for the detailed reply. I won't have aircon; most of the world gets by without it, and the cost isn't worth it for me. Besides, I'll visit boats and buildings that do have it...That kills one of the big advantages then.



Instant on-demand power for maneuvering; By simply flicking a switch I have power at the prop. No starting, no warmup, no danger of cruddy fuel clogging injectors in lumpy seas (eg bar crossing) just when I need the motor most. If you are comparing a poorly maintained diesel drivetrain to a well maintained diesel-electric system, you are correct. I would assume both are well maintained or both are poorly maintained. In an emergency, I'm not waiting for warm up. I'm hitting the key and throwing her in gear within a couple seconds.

Diesels have a rev-range where they are happiest. How that gets transmitted to the water is another kind of beast. If it were that inefficient, there wouldn't be so many large d-e systems. It is only in its infancy on small private boats. If you are refering to trains and ships running diesel-electric, it is a completely different beast. It doesn't scale down to small pleasure boats. They are mostly about the complications of providing a mechanical transmission for huge drivetrains. Diesels do have a happy rev range and the beauty of a displacement cruising boat is they are set up to run right in that range when at cruising speed and that's where they spend 95% of their time when the motor is on.

Solar sailing is a little like motor sailing, only silent and cheap; propulsion wise there isn't much thrust, but it does supply enough to cancel out the drag of a prop, and anything more contributes to canceling out hull drag and begins increasing the apparent wind. Since the battery bank is relatively small for a d-e installation, it charges relatively quickly without having acres of silicon. So it basicaly it provides negligible propulsion benefits. Maybe the equivilent of a folding prop but with more complications.

The trash pump is backup for the bilge pumps and the shaft pump on the propulsion motor. Multiple ways to get the water out...a good thing! It also protects the motor itself, because if things get that sporty, it will be vital to keep it running. There will be enough flotation to spare to keep the boat afloat, and I'd rather have as much self-sufficiency as possible. This isn't a coastal cruiser and I'm not including any outside help as anything but a bonus. Who knows, off the beaten track I might be the rescuer with this kind of gear. Basically the motor runs and provides power or if it doesn't, the pumps go dead pretty quick. Doesn't matter if you convert the diesel power to electric power before using it or not. Actually a mechanical pump has the advantage that if the engine remains running but the electrical system fails, you still have pumping capability.

High torque at low speed; diesels don't like low speed. I'm talking less than idling speed, 800rpm or less. Getting a consistent quarter or half knot is more controllable than having to blip the throttle on a diesel. Also, it's silent, which the anchorage neighbours will appreciate. Most boats need at least 2-3kts to maintain control and thats easily attainable with a typical diesel drivetrain. At 1/4kt, you may as well be adrift as wind and current will have far more effect than the engine. Never heard of anyone getting offended because someone pulled into an anchorage under power. Some get offended if you run a generator all night but never heard of complaints just pulling in and getting anchored.

The electric drive motor will be around 7.5kW. Plenty enough for this size boat. It's 50/50 whether I go with a motor at all but if I do, this is how it will be. It is a new build, so I can place the heavy things where they are best integrated into the whole. 40hp is way too much for 26 feet and about 5.5 tons. 20 is more like it. Agreed 40hp is too much for a 26' boat but the drivetrain type doesn't change that.

No through hulls and no engine plumbing greatly simplifies the system. The penalty is as you say in space, but since I can put the motor where I want, I can also choose the best way to supply cooling and combustion air, in such as way as to minimise the risk of taking in water, either flooding or corrosion. Bilge pump drain goes into the cockpit, and if I want raw salt water for washing I'll live with the inconvenience of pumping it into a temporary holding tank from a hose through the cockpit drain...I wouldn't hold on to it more than a day, it'll stink. With 0 through-hulls there is that much less chance of sinking. The air intakes and exhaust are in a spot that, if it is getting green water, I won't be running the diesel anyway, and will likely have other problems...at 140 degrees list. The battery electric will still run, though....No disagreement but this is an issue of designing from the ground up to be air cooled/dry exhaust not because it's diesel electric. The engine is typically one of the heaviest items on the boat so you still want it down low to keep the center of gravity where it belongs. [/QUOTE]

When we get batteries that are even half as energy dense as diesel fuel and reasonably priced, the game will change. Until then an electric drivertrain provides almost no advantages and a lot of disadvantages.
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Old 19-08-2015, 09:53   #13
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Re: Electric Inboard

[QUOTE=valhalla360;1894603]
Quote:
Originally Posted by micah719 View Post
Thanks for the detailed reply. I won't have aircon; most of the world gets by without it, and the cost isn't worth it for me. Besides, I'll visit boats and buildings that do have it...That kills one of the big advantages then.



Instant on-demand power for maneuvering; By simply flicking a switch I have power at the prop. No starting, no warmup, no danger of cruddy fuel clogging injectors in lumpy seas (eg bar crossing) just when I need the motor most. [COLOR=red]If you are comparing a poorly maintained diesel drivetrain to a well maintained diesel-electric system, you are correct. I would assume both are well maintained or both are poorly maintained. In an emergency, I'm not waiting for warm up. I'm hitting the key and throwing her in gear within a couple seconds.[/COLOR]

Your diesel will not like you, though your mechanic will.

Diesels have a rev-range where they are happiest. How that gets transmitted to the water is another kind of beast. If it were that inefficient, there wouldn't be so many large d-e systems. It is only in its infancy on small private boats. If you are refering to trains and ships running diesel-electric, it is a completely different beast. It doesn't scale down to small pleasure boats. They are mostly about the complications of providing a mechanical transmission for huge drivetrains. Diesels do have a happy rev range and the beauty of a displacement cruising boat is they are set up to run right in that range when at cruising speed and that's where they spend 95% of their time when the motor is on.

But not in close quarters maneuvering...unless you intend to do that at hull speed?

Solar sailing is a little like motor sailing, only silent and cheap; propulsion wise there isn't much thrust, but it does supply enough to cancel out the drag of a prop, and anything more contributes to canceling out hull drag and begins increasing the apparent wind. Since the battery bank is relatively small for a d-e installation, it charges relatively quickly without having acres of silicon. So it basicaly it provides negligible propulsion benefits. Maybe the equivilent of a folding prop but with more complications.

Much better than a folding prop, and taking into account all the other implications, still a good thing.


The trash pump is backup for the bilge pumps and the shaft pump on the propulsion motor. Multiple ways to get the water out...a good thing! It also protects the motor itself, because if things get that sporty, it will be vital to keep it running. There will be enough flotation to spare to keep the boat afloat, and I'd rather have as much self-sufficiency as possible. This isn't a coastal cruiser and I'm not including any outside help as anything but a bonus. Who knows, off the beaten track I might be the rescuer with this kind of gear. Basically the motor runs and provides power or if it doesn't, the pumps go dead pretty quick. Doesn't matter if you convert the diesel power to electric power before using it or not. Actually a mechanical pump has the advantage that if the engine remains running but the electrical system fails, you still have pumping capability.

Hence the trash pump on a PTO...simultaneously pumping the water and also safeguarding the pump...and not likely to choke on the 50 pounds of tobacco tins floating about my dishevelled cabin. Oh the horror of it all...

High torque at low speed; diesels don't like low speed. I'm talking less than idling speed, 800rpm or less. Getting a consistent quarter or half knot is more controllable than having to blip the throttle on a diesel. Also, it's silent, which the anchorage neighbours will appreciate. Most boats need at least 2-3kts to maintain control and thats easily attainable with a typical diesel drivetrain. At 1/4kt, you may as well be adrift as wind and current will have far more effect than the engine. Never heard of anyone getting offended because someone pulled into an anchorage under power. Some get offended if you run a generator all night but never heard of complaints just pulling in and getting anchored.

These are cruisers. Surely you've met some here? Some of them will complain because you gave them nothing to complain about. People are like that. Totally silent, low speed control. Spectators will fall asleep watching you maneuver.


The electric drive motor will be around 7.5kW. Plenty enough for this size boat. It's 50/50 whether I go with a motor at all but if I do, this is how it will be. It is a new build, so I can place the heavy things where they are best integrated into the whole. 40hp is way too much for 26 feet and about 5.5 tons. 20 is more like it. Agreed 40hp is too much for a 26' boat but the drivetrain type doesn't change that.

Converting electric kW to direct drive combustion engine kW is a big jump. Not really comparing like with like.

No through hulls and no engine plumbing greatly simplifies the system. The penalty is as you say in space, but since I can put the motor where I want, I can also choose the best way to supply cooling and combustion air, in such as way as to minimise the risk of taking in water, either flooding or corrosion. Bilge pump drain goes into the cockpit, and if I want raw salt water for washing I'll live with the inconvenience of pumping it into a temporary holding tank from a hose through the cockpit drain...I wouldn't hold on to it more than a day, it'll stink. With 0 through-hulls there is that much less chance of sinking. The air intakes and exhaust are in a spot that, if it is getting green water, I won't be running the diesel anyway, and will likely have other problems...at 140 degrees list. The battery electric will still run, though....No disagreement but this is an issue of designing from the ground up to be air cooled/dry exhaust not because it's diesel electric. The engine is typically one of the heaviest items on the boat so you still want it down low to keep the center of gravity where it belongs. [/QUOTE]

Yep. A boat is an organism, everything has to work together.

When we get batteries that are even half as energy dense as diesel fuel and reasonably priced, the game will change. Until then an electric drivertrain provides almost no advantages and a lot of disadvantages.
Plenty of advantages, and everything has negatives. How to balance them? How to make a suit fit you? Will it fit everyone? No.
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Old 19-08-2015, 10:08   #14
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Re: Electric Inboard

hey Valhalla,


question, since you seem up on the negatives of electric propulsion. I like the idea of it as many people do, but I see and understand the limitations. I have an old cat that uses twin 39 HP sail drives. My idea ,fortunately or unfortunately I don't have the funds but, would be to replace one of my engines/sail drives with an electric for those quiet electric motor sailing moments and advantages. That will give me one efficient diesel engine to motor long distances as necessary and an easy engine for parts or technical assistance. A cat also has the advantage of area for many solar panels, 1,000 watts or more doable on most, so that should help in the recharging of the batteries.


quiet electric sounds so good!
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Old 19-08-2015, 10:09   #15
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Re: Electric Inboard

[QUOTE=valhalla360;1894603]
Quote:
Originally Posted by micah719
Thanks for the detailed reply. I won't have aircon; most of the world gets by without it, and the cost isn't worth it for me. Besides, I'll visit boats and buildings that do have it...That kills one of the big advantages then.



Instant on-demand power for maneuvering; By simply flicking a switch I have power at the prop. No starting, no warmup, no danger of cruddy fuel clogging injectors in lumpy seas (eg bar crossing) just when I need the motor most. [COLOR=red]If you are comparing a poorly maintained diesel drivetrain to a well maintained diesel-electric system, you are correct. I would assume both are well maintained or both are poorly maintained. In an emergency, I'm not waiting for warm up. I'm hitting the key and throwing her in gear within a couple seconds.[/COLOR]

Your diesel will not like you, though your mechanic will. If you do it regularly, yes it's hard on the engine. If you do it occasionally in an emergency sitation, it's pretty harmless.

Diesels have a rev-range where they are happiest. How that gets transmitted to the water is another kind of beast. If it were that inefficient, there wouldn't be so many large d-e systems. It is only in its infancy on small private boats. If you are refering to trains and ships running diesel-electric, it is a completely different beast. It doesn't scale down to small pleasure boats. They are mostly about the complications of providing a mechanical transmission for huge drivetrains. Diesels do have a happy rev range and the beauty of a displacement cruising boat is they are set up to run right in that range when at cruising speed and that's where they spend 95% of their time when the motor is on.

But not in close quarters maneuvering...unless you intend to do that at hull speed? Sure but you don't burn much fuel to begin with close quarters manuvering so even if there were huge efficency gains, reducing 0.1gals per month to 0.05 gals per month is pretty much irrelevant. Reality is the vast majority of fuel is burnt at cruising speed.

Solar sailing is a little like motor sailing, only silent and cheap; propulsion wise there isn't much thrust, but it does supply enough to cancel out the drag of a prop, and anything more contributes to canceling out hull drag and begins increasing the apparent wind. Since the battery bank is relatively small for a d-e installation, it charges relatively quickly without having acres of silicon. So it basicaly it provides negligible propulsion benefits. Maybe the equivilent of a folding prop but with more complications.

Much better than a folding prop, and taking into account all the other implications, still a good thing. Run the numbers on the wattage put out by say a 200watt solar array and how much fuel will be saved. In theory it sounds good but there just isn't that much power being generated.


The trash pump is backup for the bilge pumps and the shaft pump on the propulsion motor. Multiple ways to get the water out...a good thing! It also protects the motor itself, because if things get that sporty, it will be vital to keep it running. There will be enough flotation to spare to keep the boat afloat, and I'd rather have as much self-sufficiency as possible. This isn't a coastal cruiser and I'm not including any outside help as anything but a bonus. Who knows, off the beaten track I might be the rescuer with this kind of gear. Basically the motor runs and provides power or if it doesn't, the pumps go dead pretty quick. Doesn't matter if you convert the diesel power to electric power before using it or not. Actually a mechanical pump has the advantage that if the engine remains running but the electrical system fails, you still have pumping capability.

Hence the trash pump on a PTO...simultaneously pumping the water and also safeguarding the pump...and not likely to choke on the 50 pounds of tobacco tins floating about my dishevelled cabin. Oh the horror of it all...Reality is you are far from a typical cruising boat, particularly if you are in the 26' range. Most have a couple electric bilge pumps and call it good. What you are suggesting can be done regardless of drivetrain style but almost no one does.

High torque at low speed; diesels don't like low speed. I'm talking less than idling speed, 800rpm or less. Getting a consistent quarter or half knot is more controllable than having to blip the throttle on a diesel. Also, it's silent, which the anchorage neighbours will appreciate. Most boats need at least 2-3kts to maintain control and thats easily attainable with a typical diesel drivetrain. At 1/4kt, you may as well be adrift as wind and current will have far more effect than the engine. Never heard of anyone getting offended because someone pulled into an anchorage under power. Some get offended if you run a generator all night but never heard of complaints just pulling in and getting anchored.

These are cruisers. Surely you've met some here? Some of them will complain because you gave them nothing to complain about. People are like that. Totally silent, low speed control. Spectators will fall asleep watching you maneuver. Nope been cruising for close to 20yrs with the last 10 liveaboard. Never once heard someone complain because another cruiser used the engine to come into an anchorage. In fact, I can't say that I even hear the engine typically. I do often hear the electric bow thrusters though, not that it bothers me or anyone else.


The electric drive motor will be around 7.5kW. Plenty enough for this size boat. It's 50/50 whether I go with a motor at all but if I do, this is how it will be. It is a new build, so I can place the heavy things where they are best integrated into the whole. 40hp is way too much for 26 feet and about 5.5 tons. 20 is more like it. Agreed 40hp is too much for a 26' boat but the drivetrain type doesn't change that.

Converting electric kW to direct drive combustion engine kW is a big jump. Not really comparing like with like. True, you can probably get away with a slightly smaller direct drive diesel than a diesel-electric generator but it's really not enough to worry about. (see my earlier post about hybrid cars for an explanation)

No through hulls and no engine plumbing greatly simplifies the system. The penalty is as you say in space, but since I can put the motor where I want, I can also choose the best way to supply cooling and combustion air, in such as way as to minimise the risk of taking in water, either flooding or corrosion. Bilge pump drain goes into the cockpit, and if I want raw salt water for washing I'll live with the inconvenience of pumping it into a temporary holding tank from a hose through the cockpit drain...I wouldn't hold on to it more than a day, it'll stink. With 0 through-hulls there is that much less chance of sinking. The air intakes and exhaust are in a spot that, if it is getting green water, I won't be running the diesel anyway, and will likely have other problems...at 140 degrees list. The battery electric will still run, though....No disagreement but this is an issue of designing from the ground up to be air cooled/dry exhaust not because it's diesel electric. The engine is typically one of the heaviest items on the boat so you still want it down low to keep the center of gravity where it belongs. [/QUOTE]

Yep. A boat is an organism, everything has to work together.

When we get batteries that are even half as energy dense as diesel fuel and reasonably priced, the game will change. Until then an electric drivertrain provides almost no advantages and a lot of disadvantages.


Plenty of advantages, and everything has negatives. How to balance them? How to make a suit fit you? Will it fit everyone? No.

Yes, you can build a diesel electric boat but so far I've yet to see someone come up with a real problem that it solves other than to say they could do it.
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