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Old 04-09-2019, 11:09   #1
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serious discussion about electric power in large boats

greetings capns
we are in the process of struggling through an engine rebuild/replacement with our 1985 Ford Lehman SP90 on our 43ft Brewer cutter centerboard, approx weight 25K.
as usual big plans with a small budget..
options to date: rebuild the Lehman replace with newer power plant ie Beta 50
In the process we continue to run into discussions re: electric power
trouble is we cant find an adult discussion about the feasibility of electric power in a vessel of our size and weight.
Our criteria: at least 100 miles cruising distance between charges
recharge capacity using 2 Kyracera 130s and Carib WindGenerator
and occasional Honda 2000i portable generator

any insight appreciated as well as experienced/knowledgable forums
its disappointing the lack of actual information and experience onhand.
thanks Tom Jones s/v Blue Trust
tj5035@gmail.com 443 454 4871


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Old 04-09-2019, 11:26   #2
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Re: serious discussion about electric power in large boats

The biggest factor is that range. For a boat of that displacement, you're looking at a massive battery bank and charging system to account for that kind of distance capability out of electric propulsion. I'm sure you'll get more feedback in regards to specifics, but talking 12+ hours of motoring out of electric propulsion is quite resource-intensive.

For example, here's a 48v kit, for about 20hp average equivalent output as an example.

https://www.thunderstruck-ev.com/ac-...601-clone.html

But when you look at the power requirements for amperage, you're looking at hundreds of amps required. Calculate that out by the length you need them to be, coupled with available capacity being 50% of your total Ah bank. You're looking at a good 2000 amp hour bank minimum, not counting other loads. Also, you now don't have an alternator on your engine to help charge your bank, so then calculate solar/wind and/or shore power to charge it back up as needed.

While it's a great idea, and if possible I would certainly agree to doing it, but if you find yourself needing the distance more often than not, you'll be more cost effective and also have the extra peace of mind knowing you have plenty of range and power by going with a replacement or rebuild of your existing engine.
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Old 04-09-2019, 11:35   #3
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Re: serious discussion about electric power in large boats

There is far more power in a pound of diesel fuel than there is in a pound of batteries. Stick with a diesel.

Betamarine 50 is a great engine. I have had one for the last 16 years - replaced a Perkins 4-108 and it was an excellent decision.
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Old 04-09-2019, 12:15   #4
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Re: serious discussion about electric power in large boats

For that boat, folks would recommend at least a 40HP diesel, right?

Let's be overoptimistic and assume you only need half that to get to a useable cruising speed (5mph?), so 20HP.

At 5mph, it'll take you 20 hours to get your 100 miles. So the energy you need for your journey is (20 HP) times (20 hours).

20HP = 15 kilowatts. So you need 15 kilowatts * 20 hours = 300 kilowatt hours of energy to make your 100 mile journey.

300,000 watt hours / 12 volts = a 25,000 amp hour 12V battery bank..

(if you are thinking "but wait, i'll be charging along the way", just remember: Your panels are 0.13 kilowatts. You need 15 kilowatts. They aren't making a dent for charging en route.)

That's amazing, right? Almost makes me think I have an arithmetic error here. But let's do it another way. Let's find out how much battery capacity I need to replace 1 us gallon of diesel fuel.

1 gallon of diesel = 139,000 btu = 40 kilowatt hours. Even if the electric system is 100% efficient, and the diesel is only 33% efficient, you are talking (40kw * 0.33)/12V = 1,100 _usable_ amp hours of capacity to replace one gallon of diesel fuel. Wow!

Another way of looking at it: Your 130 watt panel, in perfectly bright sunny conditions, will take 40kwh / .13kw = over 300 hours to produce the energy of _one gallon_ of diesel fuel. Again, if the electrical system is 100% efficient, and the diesel is only 33% efficient, that's still 100 hours to replace one gallon of diesel! Wow!
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Old 04-09-2019, 12:29   #5
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Re: serious discussion about electric power in large boats

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Originally Posted by tom jones View Post
any insight appreciated as well as experienced/knowledgable forums
its disappointing the lack of actual information and experience onhand.

Have you read the previous several long threads already here on CF?

IIRC, some of those also include links to actual examples...

-Chris
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Old 04-09-2019, 12:59   #6
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Re: serious discussion about electric power in large boats

Energy density in fossil fuels is what will keep them around for a very long time.

Check out this conversion site (right side of table - only insert one variable) and you will see you need 4kwh to produce about 5hp of power, which will push your boat at around 5 to 5-1/2 kts for one hour in flat water. 4kwh power will take either (i) 13 300W solar panels; or (ii) 3-1/4 batteries (100A each); or (iii) some combination of both.

Will take you about 15-hours to run 100nms at 6-kts, so you can multiple the above by 15. You can see the problem with scale - all this to displace about 15-gallons of diesel (1gph at 6-kts). Now, I'm sure the math is off by a little here and there, but still - it takes a massive amount of solar/battery to displace the energy in a single gallon of diesel fuel.

But there is some hope - diesel electric has been used in locomotives and ship propulsion for a long time, and some of that technology is seeping into recreational boats, though I am told that there is a meaningful efficiency loss going from one flavor of power (internal combustion) to another (electric) which has moderated successful implementations. But this is an interesting article on a trawler-yacht conversion that sounded promising when I first read it in 2011:

https://www.agbm.fr/attachment/387917/

It's a 42-foot Grand Banks trawler yacht that had a pair of 210 Cummins in her that were replaced by a single 300hp Volvo driving a 100kw DC generator and a massive 360V battery bank. The company - ReGen Nautic - states a conversion is in the $80k range, though their website is no longer active so perhaps they are out of business.
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Old 04-09-2019, 13:48   #7
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Re: serious discussion about electric power in large boats

thanks chris thought we did, but ill check more carefully. tom
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Old 04-09-2019, 14:11   #8
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Re: serious discussion about electric power in large boats

TJ, there are a couple of sites/forums you may want to look into. Electricseas.org & yahoo has a electric boat group.

Far as 100 miles between charges, unless you have a big ass battery bank, not going to happen. If you have a battery bank large enough to get you 100 miles down the road, it will take days to charge it back up with only 260 watts of solar.

Furthest I've ever "motored" was 21 NM & my bank had 10% capacity left. I have a 150 AH 48 volt bank & under normal use can bring it back up to 100% in a couple days providing I don't beat the snot out of it
I have 200 watts of 24 volt volt panels wired in series. I do have a honda 2200 watt generator but hate running the dam thing. Seems my biggest draw on the propulsion bank when not trying to get somewhere is for the water heater. I put a 48 volt, 1000 watt element in it, nice having hot water on a 28' boat.

Unlike an ICE, the faster you go, faster the battery bank depletes. Personally I'm pretty happy going the electric route but it does have limitations & so far I'm content living with it.
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Old 04-09-2019, 15:24   #9
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Re: serious discussion about electric power in large boats

I'm a solar/electric guy through and through, and I often think of how great it would be to ditch the stinky diesel along with associated oil drips, exhaust and cooling water systems, etc. etc. for a nice tidy electric drivetrain if my Perkins 4108 ever gives up the ghost...

I'd do it if I didn't need more than 20-30nm of range, for all the reasons above. 100nm is just a lot of energy for batteries to store, and your PV array isn't big enough to recharge it in a reasonable timeframe.

That said, batteries are getting cheaper quite quickly, so that 20-30nm threshold in my mind creeps up every year. EVs are driving really sharp reductions in Li-ion battery costs, including LFP, which is more suitable for use on boats. At large volumes, we're starting to see LFP get close to the $100/kWh level, meaning you could (maybe in 5yrs?) get close to 100nm range in a ~100kWh pack for $10k (really really round numbers). If the motor is another few thousand, if you squint a bit it makes sense for some people.

The dream for me would be to combine the electric drivetrain with, say, 1000kW of PV, induction cooktop to ditch propane, and electric dinghy motor - so no fuels at all. With a water maker you could then cruise almost indefinitely without resupply - you just couldn't motor for very long. Which would be fine because in my dream I wouldn't have anywhere I'd need to get to...

So yeah, not there yet for most use cases, but there is a small number of very specific use cases where it does make sense, and that number grows every year with the continuing decline of solar and storage prices.
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Old 05-09-2019, 07:58   #10
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Re: serious discussion about electric power in large boats

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Far as 100 miles between charges, unless you have a big ass battery bank, not going to happen. If you have a battery bank large enough to get you 100 miles down the road, it will take days to charge it back up with only 260 watts of solar.
I'm not sure "days" describes it properly.

Even if we use your 5 horsepower figure (which is obviously inadequate for a ship this size, but what the hell, let's be optimists) we are talking

5hp * (745 watts per hp) = 3725 watts of power

Now if we use your trip time, and optimistically assume that this 5hp motor is somehow going to move this ship 100 miles in 15 hours, we are up to

3725 watts * 15 hours = 55875 watt*hours of energy

Now we've got 260 watts of solar, so we hook up our magic, 100% efficient solar charger, and it'll still take 55875 watt*hours / 260 watt = 214 hours of direct sunlight.

Figuring optimistically that we get the equivalent of 8 hours of direct sunlight on those panels per day, it'll take 26 days to charge up.
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Old 05-09-2019, 08:33   #11
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Re: serious discussion about electric power in large boats

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For that boat, folks would recommend at least a 40HP diesel, right?

Let's be overoptimistic and assume you only need half that to get to a useable cruising speed (5mph?), so 20HP.

At 5mph, it'll take you 20 hours to get your 100 miles. So the energy you need for your journey is (20 HP) times (20 hours).

20HP = 15 kilowatts. So you need 15 kilowatts * 20 hours = 300 kilowatt hours of energy to make your 100 mile journey.

300,000 watt hours / 12 volts = a 25,000 amp hour 12V battery bank..

(if you are thinking "but wait, i'll be charging along the way", just remember: Your panels are 0.13 kilowatts. You need 15 kilowatts. They aren't making a dent for charging en route.)

That's amazing, right? Almost makes me think I have an arithmetic error here. But let's do it another way. Let's find out how much battery capacity I need to replace 1 us gallon of diesel fuel.

1 gallon of diesel = 139,000 btu = 40 kilowatt hours. Even if the electric system is 100% efficient, and the diesel is only 33% efficient, you are talking (40kw * 0.33)/12V = 1,100 _usable_ amp hours of capacity to replace one gallon of diesel fuel. Wow!

Another way of looking at it: Your 130 watt panel, in perfectly bright sunny conditions, will take 40kwh / .13kw = over 300 hours to produce the energy of _one gallon_ of diesel fuel. Again, if the electrical system is 100% efficient, and the diesel is only 33% efficient, that's still 100 hours to replace one gallon of diesel! Wow!
Swell nailed it on the head. I am a senior executive of a company that designs and manufactures electric motors and drive systems for electric vehicles [eBuses, eTrucks] and generators. Our firm is part of a consortium of the world's largest lithium battery manufacturer, the world's largest electric bus manufacturer and a major drive train manufacturer [axle, suspension, CV and differential]. When one transitions from terrestrial electric vehicles to eMarine sector one must keep in mind that with a boat one is displacing water so as to float the boat with its massively heavy battery system, and not displacing just air. And that one has to displace pound for pound, kilogram for kilogram with a boat and that one has to move aside such poundage / kilogram of water every inch the boat moves through the water. The work effort involved in eMarine is immense compared to the work effort in driving a vehicle on a smooth roadway. For short distance navigation eMarine is very viable when the vessel can rapidly recharge from shorebased power sources, for example, ferry boats, harbor service boats but eMarine does not have the energy storage capabilities yet. Hybrid drive schemes are being developed, such as hydrogen FCEV [Fuel Cell Electric Vehicles]. In the early years of our motor design company, we developed motors for US Navy shipboard applications whereby our motors displaced traditional induction motors used for powering Heating, Ventilation , Air Conditioning [cooling and dehumidification] systems onboard. Our motors were typically about 1/5th to 1/6th the size and weight of the traditional induction motors that the navy ships were previously equipped with. We were able to shed many tens of thousands of poundage of weight onboard the vessels when retrofitting older ships and provisioning newer ships HVAC systems. That was tens of thousands of pounds of water that did not need to be displaced every inch the navy ships transited which lack of water displacement realized a tremendous improvement in the total efficiency of the ship's performance, whereas our motors and controls provided incremental improvement in the variable speed / torque performance compared to the traditional induction motors which motors are quite inefficient when operated at below their rated speed and power which is the situation for most of the time of operating HVAC systems because the HVAC systems are designed for achieving peak climate load capacities when it is extremely hot or extremely cold.

For your everyday cruisers, eMarine is just not ready to displace combustion powered systems. I wish is was because we would enjoy developing systems for recreational boats.
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Old 05-09-2019, 09:37   #12
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Re: serious discussion about electric power in large boats

Yeah, it is hard to have an adult conversation about it. I heard a lot of naysayers tell me I was nuts for converting to electric, but it has worked out well for me. It is highly dependent on what your needs are. I don't need to go anywhere in a hurry, 4 to 5 knots is more than enough in my 37 ft boat. My range without a gen is about 20 NM at 4 kts. It costs me about a dollar for charging at my dock for that. No smell. Quiet. Clean. No maintenance. I carry a generator (portable) to extend the range to whatever I need depending on how much fuel I want to burn. So far (after 6 mo) haven't fired it up except to test it. It's a sailboat! Not regretting it one bit! That said, if you motor more than sail, and motor long distances, stick with the diesel. For me the tradeoffs were totally worth it to go electric.
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Old 05-09-2019, 10:43   #13
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Re: serious discussion about electric power in large boats

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Yeah, it is hard to have an adult conversation about it. I heard a lot of naysayers tell me I was nuts for converting to electric, but it has worked out well for me. It is highly dependent on what your needs are. I don't need to go anywhere in a hurry, 4 to 5 knots is more than enough in my 37 ft boat. My range without a gen is about 20 NM at 4 kts. It costs me about a dollar for charging at my dock for that. No smell. Quiet. Clean. No maintenance. I carry a generator (portable) to extend the range to whatever I need depending on how much fuel I want to burn. So far (after 6 mo) haven't fired it up except to test it. It's a sailboat! Not regretting it one bit! That said, if you motor more than sail, and motor long distances, stick with the diesel. For me the tradeoffs were totally worth it to go electric.



SIEVE, love your response. Have been watching "Sailing Uma" and take note of their attitude that they're not going to try and outrun a storm or beat into a headwind because sailing is a leisurely activity and down time is quite OK. Am keen on switching the Yanmar for an electric engine on my 28 foot Morgan Out Island but still not sure if I have space for enough solar panels to recharge batteries if I'm not tied to shore power. Can you tell us anything about the electric motor you selected and the numbers and strength of solar panels and batteries?
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Old 05-09-2019, 10:57   #14
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Re: serious discussion about electric power in large boats

I think the others have said it but I'll restate it just for the record.


First my degree is EE and I would love to go electric but won't for all the reasons already stated.


1. Range. You would have to fill you entire boat with batteries or add a generator to reliably get more than 10-30 miles range under power and that assumes under power at very moderate speeds and in calm conditions.


2. Cost.



a) Don't know why but all the "marine" electric systems I checked a couple of years back were ridiculously expensive when you got to something with enough power to push a 40'+ boat. I looked at industrial, heavy duty, constant power ratings and found some that were 10-20% of the cost of the marine rated units. For that much savings I would just buy two or three and have spares.


b) If you did add a generator to get the range without having to add a ton (literally) of batteries the cost for the whole system could be double or triple the cost of a new diesel install.
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Old 05-09-2019, 11:34   #15
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Re: serious discussion about electric power in large boats

Yahoo has a group with lots of information on electric boats. They also have examples of conversions and performance data on those conversions. See, https://groups.yahoo.com/neo/groups/electricboats/info.
To go 100nm you are going to need a generator to power the electric motor. Like everyone else has said the battery capacity needed to go that distance would be huge! Keep in mind that with an electric conversion there are other factors to consider, like a prop conversion. There are other threads on CF that go in detail on electric conversions. Good luck!
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