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Old 03-08-2017, 11:53   #1
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It's mid-2017. Time to discuss electric propulsion again.

This has been contentiously discussed many times in the past and folks could be forgiven for thinking the case closed since diesel fuel is the safer than anything else and also has the highest energy density.

But the fact is, transportation technology is changing very rapidly.
The $/Kwh for batteries has come down precipitously and will continue to come down further.
https://electrek.co/2017/01/30/elect...-tesla-190kwh/
It's not just Tesla that has built a gigafactory. The Chinese are all over this as well.

I'm considering a re-power right now (40 year old Westerbeke 40/Perkins 4-108). There are no viable, cost effective electrical options on the market at this time (that I can see). However, the expensive part in marine electrical propulsion is the huge battery. I have to believe the marine propulsion market will be disrupted by low-cost batteries in the very near future.

Consider the side benefits:
- Effectively unlimited house battery
- Regeneration while under sail (motor acts as a generator)
- Automated efficiency optimizations - for example, the coefficient of drag is higher at higher speeds, just like in a car. So, you need to get 150nm out of your battery pack motoring into a 8kt headwind? You'll need to keep it under 4.2 kts, SOG.
- Intelligent motorsailing should have extremely low current draw.
- battery pack(s) location flexibility
- No diesel maintenance!

I think marine diesel engines will see rapid depreciation in value over the next 5 years.
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Old 03-08-2017, 16:14   #2
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Re: It's mid-2017. Time to discuss electric propulsion again.

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Originally Posted by sandmaninator View Post
However, the expensive part in marine electrical propulsion is the huge battery. I have to believe the marine propulsion market will be disrupted by low-cost batteries in the very near future.
It's not just the cost. To me the big question is how do you re-charge that huge battery when you are not tied up to a dock with shore power.
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Old 03-08-2017, 16:38   #3
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Re: It's mid-2017. Time to discuss electric propulsion again.

Certainly there are options out there but so far nothing that is cost effective, energy efficient or that charges quickly enough. I think (hope) there will be progress in this area over the next few years but not sure about that option it this time
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Old 10-08-2017, 13:42   #4
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Re: It's mid-2017. Time to discuss electric propulsion again.

I was in the same spot last year. My engine needed an overhaul and was contemplating going electric. There are lots of advantages to electric: Noise, emissions, low maintenance.

It had one very big drawback... range at higher power output. For how we use our boat that was a deal breaker. As primarily a weekend sailor having to motor into a sea or headwind is a very common occurrence for us.
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Old 10-08-2017, 15:44   #5
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Re: It's mid-2017. Time to discuss electric propulsion again.

Yeah, I hear that!
You have a week or a weekend and your guests have taken time off work to be there with you and to realize your sailing plans, you need to go into a 15kt headwind.

Been there!
To maintain 6kt boat speed in a headwind, you are looking at serious power draw.
How about this instead- motorsail on a tack. I would think that would make the power draw more reasonable. Also might be more comfortable for the guests (I have a Bristol 40 and she gains a LOT of waterline, speed and stability when she is leaned over a bit).

Oops, got a call.. will post more later
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Old 10-08-2017, 17:06   #6
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Re: It's mid-2017. Time to discuss electric propulsion again.

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Originally Posted by StuM View Post
It's not just the cost. To me the big question is how do you re-charge that huge battery when you are not tied up to a dock with shore power.


That is the issue, even with a huge Solar array your sitting a week or more charging for one day motoring, if you could get a day.
So you get a super lightweight, high performance sailboat, and use regeneration to charge the battery bank, and get passed by a 40 yr old heavy full keel boat, cause your generator slows the boat way down.

There is an application, I believe it will be the future for a day sailer, a boat that never leaves the bay and is tied up to the dock nearly every night. School boats too.
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Old 10-08-2017, 18:59   #7
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Re: It's mid-2017. Time to discuss electric propulsion again.

Don't hold your breath on battery technology catching up to diesel fuel any time soon by the way. I haven't looked at battery technology in the last year or so, so its certainly possible there is a new lab tech that has closed the gap, but the best chemistry on the shelf right now still works out to require about 40lbs of batteries for each pound of diesel (Rechargable Lithium-ion).

To make electric propulsion realistic for most people it needs to close this gap to probably 10:1 or better.
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Old 10-08-2017, 19:25   #8
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Re: It's mid-2017. Time to discuss electric propulsion again.

A modern diesel engine directly driving a propeller at constant rpm is surprisingly efficient. Using a diesel genset to make electricity and running that elecrticity through wires to an electric motor is less efficient. And using a diesel genset to charge batteries and then later use those batteries to run an electric motor is even less efficient.

Solar panels would solve the problem but there isn't nearl enough unshaded space on a boat for solar to be a practical replacement for diesel (unless you stay at anchor).

Charging batteries with shorepower where the utility made that electricity by burning fossil fuel also emits more CO2 than the diesel engine because large amounts of energy is lost in the grid and the battery charge/discharge.

I'm not aware of any new technology that changes this.
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Old 11-08-2017, 15:06   #9
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Re: It's mid-2017. Time to discuss electric propulsion again.

The latest vlog of Sailing Uma shows them lying in the heat of the day while drifting because of lack of wind. They weren't very comfortable, however it was only for a couple of hours. That was on a very short passage so don't know if they could have used the electric motor to get them to their destination or not.
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Old 12-08-2017, 08:08   #10
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Re: It's mid-2017. Time to discuss electric propulsion again.

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A modern diesel engine directly driving a propeller at constant rpm is surprisingly efficient. Using a diesel genset to make electricity and running that elecrticity through wires to an electric motor is less efficient. And using a diesel genset to charge batteries and then later use those batteries to run an electric motor is even less efficient.

Solar panels would solve the problem but there isn't nearl enough unshaded space on a boat for solar to be a practical replacement for diesel (unless you stay at anchor). Correction, there isn't enough power available from the sun to ever generate enough power from the available square footage to power marine propulsion. 100% efficient solar panels covering the entire boat, pointed optimally at the sun at all times, could generate about 1/4 the amount of power that most installed marine propulsion engines do.

Charging batteries with shorepower where the utility made that electricity by burning fossil fuel also emits more CO2 than the diesel engine because large amounts of energy is lost in the grid and the battery charge/discharge. It depends. The cleanliness of grid tie propulsion depends on where you plug your boat in. More accurately what mix of fuels your power company burns to create the power. In California, with huge amounts of renewable power grid power is far cleaner than a diesel engine. In some parts of the midwest where coal is still dominate electric propulsion is worse. As natural gas keeps making inroads in replacing coal, and more and more utilities are building out renewable power it is shifting more and more favorable to plug in power.

I'm not aware of any new technology that changes this.
The real issue for marine propulsion is energy storage. We simply do not know how to store electricity densely enough for marine propulsion. The rest of the drive train is perfected, but battery technology simply isn't there yet.
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Old 12-08-2017, 08:35   #11
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Re: It's mid-2017. Time to discuss electric propulsion again.

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It's not just the cost. To me the big question is how do you re-charge that huge battery when you are not tied up to a dock with shore power.
^^^^ THIS. It's not the electrical power itself that's limiting the electric car acceptance, it's the range. Also Tesla is said to be losing money on their "cheap" $35k recent model. Maybe that will change.
Volvo however has committed to building only electric soon. That's a gamble, and definitely may exclude them from much of the US markets as we have a lot of "wide open spaces" to travel. But for countries that are no bigger than 200 miles or so, it's cool.
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