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Old 21-06-2018, 13:02   #1
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Viability of electric only propulsion in 2018 - is there a good option after all?

This https://youtu.be/-uTy5owBsUE is a pretty good analysis of what it would mean to dispense with Diesel engines and go fully electric for propulsion.

The tldr is electric range 20nm with 4 Tesla power walls (which aren’t marine certified but are used for thought experiments sake) versus 800nm with the 700 liter diesel tank of the leopard 45. (Its 800nm at 5 knots or 400nm at close to 8 knots, more on that later)

OUCH!

Double ouch because 4 Tesla power walls provide enough power to supply 3 single family homes with enough power for 24 hours.

That really is a shame, it seems to me that not only is electric a more elegant solution (more quiet, no smelly exhaust) but has so many benefits. Feel free to correct me if I’m wrong or missing something

- maintenance on a electric drive train is less complicated because they are mechanically much simpler, engines last longer
- engines like the oceanvolt servoprop can double as hydrogenerators when not in use without clumsy mechanisms to lower them into the water (I’m looking at you watt&more)
- having a large battery bank for engines provides a big comfort bonus and gives you a lifestyle close to onshore living

But... Is there another option that would give a similar range than Diesel engines?

I did some quick napkin math.

The above mentioned oceanvolt Servoprop has a 15kw engine. According to some online resources a 20kw generator (so we have some spare capacity) uses about 1.6 gallons/ 6.4 liters per hour at full load. That means you could run it for about 109 hours on above mentioned 700 liter tank.

Ocean volt specs say the max Speed of a servo prop on a 45 foot multihull is about 8.5 knots.

Let’s assume 8 knots sustained is realistic. This would give you a range of 872 nm - which is not only a superior range to diesel but at almost twice the speed on top of it. And the 872nm are not the hard limit of the range but only what you could do in “one go”. You would still be able to do 20nm indefinitely per recharge cycle if you have wind to hydro generate or solar.

So is hybrid the way to go? Even if running a single generator still means relying on diesel, it is easier, quieter, requires less maintenance than running 2 large Diesel engines

Certainly, the initial purchasing cost is higher but you would likely find the 20nm range provided by hydro generated power sufficient in most cases for things like getting back to the Marina or get into the wind so this would amortize against reduced diesel cost.

Am I missing something?

Shouldn’t this be the holy grail of sailing propulsion?
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Old 22-06-2018, 04:58   #2
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Re: Viability of electric only propulsion in 2018 - is there a good option after all?

Did you read all the other threads on electric propulsion before posting?

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Old 22-06-2018, 06:30   #3
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Re: Viability of electric only propulsion in 2018 - is there a good option after all?

I don't know what kind of napkin you work on, but think for a minute about what you are saying...

You are proposing to take diesel fuel and converting it to mechanical energy, then into electrical energy, then store that energy, then pull it out of storage, convert its voltage and or frequency, and then convert it back to mechanical energy...

And you honestly believe that will be more efficient than taking diesel fuel and converting it to mechanical energy?

I am guessing you are not an engineer...

Go read the other 40000 forum posts on this topic... You'll find lots people presenting of lots of good data, and lots of people who BELIEVE what you propose SHOULD work. They are not the same people
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Old 22-06-2018, 06:40   #4
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Re: Viability of electric only propulsion in 2018 - is there a good option after all?

Do some research on Nordhavn's experience with the diesel electric concept. It wasn't pretty. Those boats now have reliable, conventional power. Diesel electric has benefits where there is a high house load and variable needs for propulsion, think cruise ships; but, it is not a good fit for small yachts.

A better and more realistic goal is lots of solar and little to no use of a generator. Why take risks and add complexity to propulsion when the reliability could mean life and death (or at a minimum the safety of the vessel)?
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Old 22-06-2018, 07:42   #5
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Re: Viability of electric only propulsion in 2018 - is there a good option after all?

Quote:
Originally Posted by billknny View Post
You are proposing to take diesel fuel and converting it to mechanical energy, then into electrical energy, then store that energy, then pull it out of storage, convert its voltage and or frequency, and then convert it back to mechanical energy...

And you honestly believe that will be more efficient than taking diesel fuel and converting it to mechanical energy?

I am guessing you are not an engineer...

This!





"Ocean volt specs marketing hype say" (There fixed it for you)


You really should read some of the previous long threads on the subject. There are valid use cases for electric propulsion - long range motoring is definitely NOT one of them.
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Old 22-06-2018, 09:33   #6
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Re: Viability of electric only propulsion in 2018 - is there a good option after all?

Why not split the difference in a cruising cat. With one side fully electric you can create a large house/e-motor bank and produce electricity efficiently under sail for charging and all your underway needs as well. Use enough solar to take care of business at anchor and you would not need a generator.

With the other side diesel you could have a large alternator for emergency charging, have the long distance range (cats normally only motor on one engine anyway) and still maintain the maneuverability in and out of port.

This would give you less fuel consumption, less maintenance and plenty of electricity.

I can not be the only one to think of this yet no one is taking this approach. I don't see any technical problems with this on the surface but I am no expert in either. Someone please help me understand what I am missing here.
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Old 22-06-2018, 17:46   #7
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Re: Viability of electric only propulsion in 2018 - is there a good option after all?

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cats normally only motor on one engine anyway Someone please help me understand what I am missing here.

Huh??
You must like going in circles to nowhere.
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Old 22-06-2018, 17:55   #8
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Re: Viability of electric only propulsion in 2018 - is there a good option after all?

There is only one problem that nobody tells about electric .

What happens in case of a flood ?
The diesel motor will continue to work until the air intake gets flooded , it can be use as an extra bilge pump and most of the times is easily repaired even flooded , plus provides bigger distance .


I love electric but for now is only helpful in a hybrid model , electric for small distances or to move in an out the marina , and for the rest diesel.
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Old 22-06-2018, 18:00   #9
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Re: Viability of electric only propulsion in 2018 - is there a good option after all?

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Huh??
You must like going in circles to nowhere.

Most cat cruisers only use both engines for manouvering or when they need lots of power in more extreme conditions. The vast majority of time under engine is indeed on one.
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Old 22-06-2018, 19:05   #10
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Re: Viability of electric only propulsion in 2018 - is there a good option after all?

Iglo, first, Welcome to CF!

You're right that electric would be nice, but you need to realize that ServoProp wants to sell product, so you need to take their "specs" with a HUGE grain of salt. There's no way that a 15kw motor (20hp) will get a 45' cruising cat up to 8.5 knots. We have 2x50hp diesel engines, & our top end under motor is ~9 knots. And we never go there, as it chews through fuel. We're quite happy motoring at 5 knots on 1 engine at 2 L/h (assuming we can't sail, of course!)

As others have said, there's a TON of posts on this subject. One of the problems with CF is that anyone can post, so sorting out those who *know* from those who want (or simply have an opinion) can be difficult, so a bit of experience helps.

FWIW, at present it seems that electric might be good for day-sails from a marina (where you can recharge) but for distance cruising you still need horsepower to move a boat, & it's hard to beat diesel. Still, it's an area that many folks (including us) are keeping an eye on.
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Old 22-06-2018, 21:30   #11
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Re: Viability of electric only propulsion in 2018 - is there a good option after all?

Yes Igloo, do read the information in previous posts about a 66 foot cruising cat ( KATO) with 15kW Oceanvolts that gets 10 knots top speed and cruises at 8.5 knots using their 11kW DC genset that uses about 4 liter/hour.

While you're at it, look up on Youtube the regeneration they get under sail. And note that is with the previous model Sd15 motors, not the Servoprop which do get the output that is in the real specifications...as validated by the judges of the DAME awards.


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Old 23-06-2018, 07:19   #12
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Re: Viability of electric only propulsion in 2018 - is there a good option after all?

It may be best to ask someone doing it.
This family are sailing on a FP Saba 50 cat, fully electric with a load of lithium batteries, solar and wind gen with diesel gen backup.
Boat name Ja Japami www.JaJapami.com
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Old 23-06-2018, 11:25   #13
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Re: Viability of electric only propulsion in 2018 - is there a good option after all?

Quote:
Originally Posted by PPLepew View Post
Huh??
You must like going in circles to nowhere.


Think it thru and it will come to you how that works.
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Old 23-06-2018, 22:51   #14
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Re: Viability of electric only propulsion in 2018 - is there a good option after all?

Jeffery O,

Das ist nicht helpful.


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Old 24-06-2018, 10:26   #15
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Viability of electric only propulsion in 2018 - is there a good option after all?

The big thing electric proponents fail to realize is that electricity doesn’t just exist in the wall, it has to be generated somehow.
Tesla automobile for example, I don’t know but have read that one model has a 200 KWH battery, and another an 85 KWH battery?
Average US house uses 30 KWH per day, so let’s replace all the gasoline cars with electric ones and save the planet, right?
Where is all this electricity going to come from? If you assume the average Tesla only uses 1/3 of its battery bank per average day, then one car uses the same power as an average house or more.
There are 2.28 autos per household in the US, your going to need to triple the electrical production or more to go to electric cars, just from a quick look.
How are you going to do that?

No, I think the way forward if you will, is not to convert to electricity, but to become more efficient if you want to be environmentally friendly.
Try this, don’t motor, sit on those days you can’t sail, and when you have to motor, slow down. 8 kts on a 45’ Boat is hugely wasteful, slow down to 4 knots and you will be amazed how little fuel you use, so little in fact and if you mostly sail, you’ll wonder what all that talk about electric propulsion is about.
Plus do we really, really need 50’ Cats etc for couples, really?
Want to be an environmentalist? Go save an old boat and cruise on it, your “footprint” is much smaller that way, but I suspect most Hollywood type environmentalists aren’t, it’s just fashionable, and they want to appear to be that way, cause what environmentalist could justify Mansions, and vacation homes etc?
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