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Old 19-08-2015, 10:30   #16
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Re: Electric Inboard

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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!
I prefer to think of it as the realistics (not negatives) of electric propulsion. The idea of throwing a few solar panels and a battery bank in and having free propulsion sounds great. The facts just don't support it without huge disadvantages.

Run the numbers on 1000watts of solar panels. It's going to put out the equivilent of maybe 1hp for 4-6hrs per day. Assuming your boat needs 10hp to maintain a slower than normal cruising speed, you would have sit for 2 days to get one hour worth of electric cruising time. Of course that ignores any electricity you use for house purposes. It also ignores losses converting it to battery storage and back to mechanical energy, so it might be 3 days to gain a single hour of slow electric cruising.

Also, don't forget that battery bank is large and expensive and needs perioidic replacement as the batteries die (ie: replacement batteries negate the fuel savings)

What you propose can be done but it's effective use is more akin to a bow thruster and you lose the redundancy of a second engine. All for a price that is likely higher than just putting two replacement diesels in.

Now if you are a weekend sailor who just needs to get in and out of harbor it's viable but you are probably burning less than 10gal of diesel per year anyway, so it's not having any significant impact on fuel costs. It also will likely hurt you come resale time as someone wanting full capability will tend to avoid a limited capability one off system. I suspect that is why most of the home built conversions are on old boats with minimal value to begin with.

Sorry if it sounds negative but the facts don't support electric propulsion for typical crusing applications.
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Old 19-08-2015, 11:57   #17
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Re: Electric Inboard

realistics , limitations, the facts, there it is. That is why it has not been done. Just kind of an old brain fart idea, sometimes they feel good! Anyway, thanks for the two cents. Need to get back to work to pay for the new mainsail coming next week. That is where the money is best used! I do want those folding props next. What is your opinion, folders or variable pitch?
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Old 19-08-2015, 13:03   #18
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Re: Electric Inboard

Let us make this real simple! I will assume 100% efficiency in all conversions and power production and we use nice new AGM batteries. I am using Victron Tubular Plate AGM battery data sheets for my source info.

My 40’ 23,000 pound Caliber 40 cutter needs 9 HP AT THE PROP! to move in still water at 5.5 knots.

9 HP = ~6.7 Kw

A 48V battery system would be four (4) 8-D batteries with 220 amp hours capacity at a 20-hour rate. If we use a one (1) hour discharge rate the safe amperage (load) is 65% of the 20-hour rate or 143 amps. That is the power we can pull from the battery for one hour without damaging it.

That means the battery bank can deliver 6.8 Kw power (9.1 HP) (143 amps x 48V) for one hour and will be at 9.6V resting voltage at the end of the hour.

For each additional hour of motoring you will need another four 8-D AGM batteries. The battery bank (four 8D) will weigh about 575 pounds and will take up 4 cubic feet of space (20” tall x 18” x 18”). The four batteries will cost $2,150, plus tax and shipping, from Jamestown Distributors.

Pulling the AGM battery down to 80% discharge, as specified above, results in about a 450 cycle life span (charge/discharge cycles) which is 1/3 of the 1,500 cycles obtained with only a 20% discharge rate.


Now, how do you recharge those things? Each battery can absorb about 110 amps during the bulk phase. That is 5.2 Kilowatts into a 48V system. Where do you get that kind of power?

Sixteen 330 watt solar panels?
A 6 Kw generator?

If you recharge with four 330 watt panels you would need Five hours of maximum sunshine to return one hour of power withdrawal from the batteries.

Bottom Line – to get one hour of slow electric motoring you need the following:

- 575 pounds of battery at a cost of $2,150
- 60 pounds of 48V motor at a cost of $500
- motor controls at a cost of $250
- 4 solar panels at a cost of $1,000
- 1 solar panel controller at a cost of $150
- Five hours of maximum sunshine
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Old 19-08-2015, 13:33   #19
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Re: Electric Inboard

Maybe those are some special AMG batteries but 80% draw down and 450 cycles seems wildly optimistic. Traditionally, you assume 30% of the amp-hr rating is available. AMG are better than old style flooded but... Even if we take it as true, assuming you travel regularly, you are looking at $2000 in replacement batteries every couple years and towards the end you may have significantly reduced range as the batteries start to wear out.

Also 5hrs maximum sunshine is about average for a full day unless you get into complicated and expensive tracking systems for the panels. Add in efficency issues and you are back up to around 2 days (ie: you can't pump 110 amps into a 90% full battery bank).

Also don't forget the mountings for 4 large 330watt panels. That could easily add a couple more grand to the price tag.

Is that $500 motor marinized to live in a damp salty bilge long term?

And we are still talking about optimistic assumptions.
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Old 19-08-2015, 15:50   #20
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Re: Electric Inboard

use lifepo4 battery...i absolutly belive in diesel-electric power and i'm planning to build my amateur boat...

hpev AC motor, lifepo4 wiston battery, 3 kw solar panel on a 46 ft trawler, 3 phase heavy duty generator + 2 14 kwh battery charger each...meaning 28kwh continuos by diesel...it's a long term investment for sure, the pro is always energy available for house load...if you think do a relaxing cruise...6 hours stop on a bay...4 hours motoring...and a new bay to enjoy...and so on

and a lot depend also where u live..

in italy diesel is like 1.50 euro/liter while in oman is 0.15euro/liter...
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Old 20-08-2015, 17:23   #21
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Re: Electric Inboard

Stefano_Ita said:

"hpev AC motor, lifepo4 wiston battery, 3 kw solar panel on a 46 ft trawler, 3 phase heavy duty generator + 2 14 kwh battery charger each...meaning 28kwh continuos by diesel...it's a long term investment for sure, the pro is always energy available for house load...if you think do a relaxing cruise...6 hours stop on a bay...4 hours motoring...and a new bay to enjoy...and so on"

It still makes no sense!

Please explain to me what is wrong with the following calculations. I may have misunderstood something because I have lived with big 12V solar arrays, Gelcell, and Lead Acid batteries for the last 15-years but no almost nothing about higher voltage LiVFePo4 systems.

Defever 46 foot trawler – assume 40’ LWL and 38,000 pounds with a 15’ beam. It needs 21 HP AT THE PROP to move at 6.6 knots in still water, which is about 15.5 Kw of power.

Let us assume a 48V high efficiency motor in which 100% of battery power gets thru to the prop.

Let us look at a LiFePo4 battery that is currently available for sale. Smart Battery SB200 8D ( 12V Lithium Ion Marine Batteries | Deep Cycle Batteries | Smart Battery® )

It is a 12V battery with a 200-amp hour capacity (8D form factor) with a max 5-hour discharge rate of 180 amps. That means you can withdraw, (until you use up the power stored in the battery), 180 amps per hour without damaging the battery.

At 48 volts and a max discharge rate of 180 amps you can produce 8.6Kw of power.

We would need 4 of those batteries to make 48 volts. Each battery weighs 78 pounds and costs about $2,400. That means the 48V battery bank weighs 312 pounds and costs $9,600.

Cruising at 6.6 knots uses 15.5 Kw and would require two (2) 48 V battery banks or a total of eight (8) 12V 200-amp hour batteries at a cost of $19,200 and 624 pounds of battery.

But, withdrawing 180 amps for one hour from a 200-amp hour battery will discharge it down to a 20% charge. That means you only can cruise for one hour at 6.6 knots before you have to recharge the batteries.

A 48V 50HP high efficiency motor with cables and controller will cost about $3,200.

The 20Kw inverter to power the AC version of that hpev motor would cost about $5,300.

You will have spent $27,700 for a propulsion system that can move the boat at 75% of hull speed for ONE (1 !! ) hour.

And, discharging to 80% of capacity used reduces the life cycle from over 3,500 charge/discharge cycles to fewer than 1,500.

You propose a 28Kw generator, which confuses me because the data sheet shows that a singe 200 amp hour 12V LiFePo4 battery can only absorb 100 amps at 14.6V or a max of 11.6Kw for the entire 800 amp hour 48V system.

The generator will recharge the batteries at about the same rate it is consumed when running at 40% power (14 HP) or about 1.4 GPH. My Yanmar only burns 0.4 GPH while producing 15 HP. You would need at least 1,600 amp hours of battery ($38,400) to accept the generator power at an efficient operating speed for the generator.

The 28Kw generator will cost at least $15,000 so the total cost of your propulsion system exceeds $27,000 and burns twice the fuel as does a direct drive diesel propulsion system.

What then is the advantage of batteries and a generator? In less than one hour (6.6 NM) of cruising on your trawler you will need to be running a 40 HP diesel engine to spin a generator that spins an electric motor that spins a prop, less efficiently that a direct drive diesel.

You plan on A 3 Kw solar array. If you use your 48V electric motor for one hour you will consume 12.5 Kw (15.5 kw to spin prop – 3 Kw produced by the solar panels while underway) of battery power and will require over FOUR (4) hours of PEAK solar power to replace the battery power consumed by one hour underway.

Where do you find five Hours (5) of peak solar panel just when you want to motor in your Trawler?

Sure - battery power backed by a generator works but it very much more expensive and far less efficient than a direct drive diesel. And, there is no reduction in carbon footprint. Those batteries, replaced every couple years under the proposed scenario, have to be made and then recycled, which is very energy consumptive.
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Old 20-08-2015, 18:15   #22
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Re: Electric Inboard

I want to clarify the the calculations I show above:

The analysis above characterised a standard form factor 8D LiFePo4 battery that appears to be about the lowest price high capacity battery available. Other, non-standard form factor LiFePo4 batteries are available can have a C factor (maximum discharge rate as a function of Ah capacity) of 3 or even 5. However, those batteries still have the same capacity limitations I show above.

For example a 200 Ah battery with a C of 5 could deliver 1000 amps (about 12 Kw) without damage BUT would still be fully discharged when 200 Ah had been consumed, which would be 12 minutes in this example.

For Example a HiPower HP-CT-200AH battery -16 cell 48V 200 Ah battery with a max C of 3 (600 amps) would cost $3,840 and would weigh 224 pounds. However, the 200 Ah Capacity is calculated at a max C of 2 (400 amps) so the battery would be fully discharged after less than 30-minutes of usage.

That battery can recharge at 200 amps up to 90% of capacity and then will dramatically taper off it's acceptance rate.

The same 16-cell 48V battery, sold by several other web sites, shows a retail price over $9,200 so I would be suspect of the very low price of $3,840.

There are many ways to arrange and manage LiFePo4 batteries but the bottom line is the capacity in AmpHours determines how long they can power the electric motor.
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Old 20-08-2015, 18:44   #23
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Re: Electric Inboard

I just wanted to point out that most of the appeal, for me, of an inboard electric system on a small sailboat is the relative ease of maintenance and the ability to replace the components on your own without spending lots of money on a diesel mechanic. I know what my friends pay to maintain the diesels in their boats and I couldn't afford it. This would be for a daysailer/coastal cruiser, though. I'm not sure I would want to do any serious offshore cruising on a boat that couldn't motor all day.

Another thing I'd like to do someday is convert an old gas vehicle to electric and have a car I could maintain myself in a similar manner. If you're interested, this is a site devoted to such exploits, and you can also see the many different components available for these conversions. BTW, many of the systems for cars (and boats) run at much higher than 48 volts.

DIY Electric Car Forums - Electric Vehicle Build and Conversion Community
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Old 20-08-2015, 20:08   #24
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Re: Electric Inboard

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I just wanted to point out that most of the appeal, for me, of an inboard electric system on a small sailboat is the relative ease of maintenance and the ability to replace the components on your own without spending lots of money on a diesel mechanic. I know what my friends pay to maintain the diesels in their boats and I couldn't afford it. This would be for a daysailer/coastal cruiser, though. I'm not sure I would want to do any serious offshore cruising on a boat that couldn't motor all day.

Another thing I'd like to do someday is convert an old gas vehicle to electric and have a car I could maintain myself in a similar manner. If you're interested, this is a site devoted to such exploits, and you can also see the many different components available for these conversions. BTW, many of the systems for cars (and boats) run at much higher than 48 volts.

DIY Electric Car Forums - Electric Vehicle Build and Conversion Community
A couple of thoughts based on my experience with diesels and electric motors. Not a motor drive for a boat but I've had to overhaul plenty of electric motors small and large, from engine starters, pumps, autopilots, dive scooters and various power tools.

If you have a diesel in decent running condition maintenance consists mainly of changing the oil, changing oil and fuel filters, bleeding the fuel lines and keeping the fuel system clean. Occasionally maybe starter, water pump or alternator. These jobs should be well within the capabilities of any reasonably skilled boater.

Also, none of these are any more complicated than maintenance on electric motors like replacing bearings and brushes which requires disassembly of the motor. Another concern, if a complex electronic controller goes out that will be far beyond the skills of anyone that isn't a skilled electronics technician.

I would agree that on average the motor itself will require less frequent maintenance than a diesel but don't forget all the other components. Think about how many threads you see on the forum asking for help with batteries, charging, wiring and all the other bits and pieces that are needed to keep electrical systems happy. Make that system higher voltage and amps and the issues grow correspondingly.

Not saying electric is a huge pain and fraught with problems, just saying it isn't lifetime, trouble free solution. Like anything on a boat, maintenance and repairs will be part of the deal.
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Old 20-08-2015, 20:23   #25
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Re: Electric Inboard

These guys are in the process of it now..

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Old 21-08-2015, 00:38   #26
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Re: Electric Inboard

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A couple of thoughts based on my experience with diesels and electric motors. Not a motor drive for a boat but I've had to overhaul plenty of electric motors small and large, from engine starters, pumps, autopilots, dive scooters and various power tools.

If you have a diesel in decent running condition maintenance consists mainly of changing the oil, changing oil and fuel filters, bleeding the fuel lines and keeping the fuel system clean. Occasionally maybe starter, water pump or alternator. These jobs should be well within the capabilities of any reasonably skilled boater.

Also, none of these are any more complicated than maintenance on electric motors like replacing bearings and brushes which requires disassembly of the motor. Another concern, if a complex electronic controller goes out that will be far beyond the skills of anyone that isn't a skilled electronics technician.

I would agree that on average the motor itself will require less frequent maintenance than a diesel but don't forget all the other components. Think about how many threads you see on the forum asking for help with batteries, charging, wiring and all the other bits and pieces that are needed to keep electrical systems happy. Make that system higher voltage and amps and the issues grow correspondingly.

Not saying electric is a huge pain and fraught with problems, just saying it isn't lifetime, trouble free solution. Like anything on a boat, maintenance and repairs will be part of the deal.
Hello everyone!

Skipmac, you are very correct on the general idea that an electric propulsion system in NOT a trouble free system. After all, it's on a boat! Ha! I'll just throw my observations into the mix and everyone can take them for what they are worth---just my two cents. Right now I am in the process of converting my Freedom 32 (Gary Hoyt design cat sloop) over to electric propulsion and my electric drive motor is already installed having replaced my Yanmar 3GM 20 HP diesel. As I'm typing this I am sitting here at home bottom balancing 32 individual Voltronix 3.2 volt 160 AH LiFePO4 prismatic battery cells in my garage. This is a VERY time consuming procedure, but one that must be done before you can assemble the all these cells into a 48 volt battery pack. (these actually test closer to 180AH!) These batteries will be wired in a 2P16S (2 parallel, 16 series) configuration for a 48 volt propulsion battery with 320 to 360 AH of capacity of which I can use 80 to 90%. If you tried discharging Lead Acid or AGM batteries to 90% they would be destroyed in no time. LiFePO4 chemistry can be discharged at up to 90%, but 80% is better for longevity, well a VERY longevity...read on. If I limit myself to an 80% discharge they have a claimed 3000 deep discharge cycle lifetime. That would be what, maybe 6 complete lead acid battery replacements over the years? If I take them to 90% that goes down to only 2,000 cycles. (only 2000? Amazing when you think of maybe 400-500 cycles with LA batteries and most don't even get that). These batteries weigh approximately 12.35 Lbs. so the complete pack comes in at 395 Lbs, and my PMAC 10.5 Kw motor and all associated pulleys, belts and mountings weighs about 60 Lbs. Compared to all the parts and systems I removed for the diesel engine I have removed a little over 300 Lbs out of the boat. That is a significant weight reduction for a 32 foot boat. Additionally the LiFePO4 battery is a two-piece setup so part of it is going right on centerline aft the mast (20 cells), and the other part (12 cells) is going under the dinette on the port side to offset a slight list I have to starboard. The 60 Lb. motor sits on the original engine beds and with it's adjustable mountings lines up perfectly with the prop shaft.

You mention some of the maintenance required on electric motors. For propulsion we don't use brushed motors very much anymore. Supposedly they are not legal anyway for electric propulsion because of the potential for sparking brushes. Something you would not want if you have propane aboard! Yikes! So there are no brushes to replace in a PMAC motor. The only things to replace are drive belt (every few years) and two motor end bearings. However those non-maintenance bearings are good for about 10,000 hours, or in other words, probably past the lifetime of most small sailboat diesel engines, or at least way past the time to rebuild them. Oh, forgot; there is a thrust bearing with one zerk fitting that you squirt some grease into once a season. :-) So yes, most of us, as I am, are using the newer brushless 98% efficient PMAC motors. (Permanent Magnet Alternating Current). Their efficiency, and amazing torque lets me get away with replacing my Yanmar 20 HP 3GM with a 10.5 Kw PMAC motor using a Sevcon AC motor controller. There is no transmission to waste energy, but instead there is an adjustable Gilmer (cog) belt drive (like a Harley Davidson motorcycle belt drive, so you can play with the drive pulley ratios to get your motor RPM matched perfectly to your prop and hull type. The available torque at low RPM is incredible. Of course it doesn't hurt the fact that electric motors develop their maximum torque at ZERO RPM, so of course one would expect great performance at, say, what? Maybe 100-200 shaft RPM as you silently glide into your slip with full reverse power available instantly. I have a live aboard neighbor in the slip next to me. Now the wife and I can sneak out of the slip for our night time harbor cruise without him even knowing we've left. No engine noise!

Regarding the maintenance?
I have given up the following diesel related maintenance; Lead acid battery maintenance (LiFePO4's are sealed chemistry and use no water), motor oil, oil changes, oil filters, fuel filters, bleeding fuel lines, water filters or cleaning strainers, impeller changes, heat exchanger maintenance, hose maintenance/replacement, tensioning/replacing belts, morse throttle and shift cables and associated parts/maintenance, no cooling water intake thru-hull, no exhaust thru-hull, no water lift muffler, no diesel fuel purchase, no fuel additives, and lastly, no more smell of diesel wafting aboard when motoring downwind, and of course the clanky pinging diesel noise.
I have yet to experience this next benefit, but one funny thing electric yachtsmen all say they notice at first when going in and out of the harbors and in close proximity to other boats is; you will notice all the people yelling their conversations over their engine noise not realizing their voices carry quite a distance. They say it's funny that they never noticed this before, because they themselves were most likely taking loudly over their own diesel engine noise too, and of course they couldn't hear the others. I am looking forward to the quiet.
I wish I could report some hard performance numbers here, but my installation is still a work in progress. However, I have used an available off the shelf system "kit" that is in wide use and there is some great well established data on it. In my case I will have so much more torque I am able to switch from my tiny 14x14 two blade prop to a new Kiwi 16.5" three blade feathering prop which should have me motoring close to 4 knots at an electric motor current drain of around 20 amps. At least this is what the other boat data curves are showing with hulls of similar displacement to mine and using the same motor system. An added benefit of the Kiwi feathering prop is that you can lock it into reverse while you are sailing, and then just like regenerative breaking works in a hybrid car, your prop shaft spins and the motor controller goes into regen mode and you are now charging your batteries while you sail. This only works well as you approach hull speed however. Larger boats could benefit more from theism but in my case I only have a 26 foot WL and thus regen will only start at boat speeds around 5 knots on up. Oh well, I'll take whatever I can get.

So, the big question is range. There were some funny range numbers posted here, but let me say this; If I can get my 4 knots at 20 amps, (fingers crossed), then with the LiFePO4 batteries having a total capacity of 320 to 360 Amp hours, at 4 knots 320 AH's (80% discharge) gives me 12.8 hours runtime at 4 knots, or about 50 miles range, and at 360 AH's (80% discharge) gives me a runtime of 14.4 hours or about 58 miles range (no wind, dead calm of course, otherwise I'd be sailing!!) Now, if I'm in a pinch and I want to go farther; at 360 AH (90% discharge) this gives me 16.2 hours runtime and a range of 64.8 miles. This is not taking into consideration that after I get my initial system up and running I plan to install two 300 watt solar panels (36 volts in series = 8A) which can either contribute to powering the boat thus increasing range, or at anchor completely recharge the entire pack in about 5 sunny days or so.

Needless to say, the new LFP battery chemistries are making this an entirely new ballgame as far as the way we think and calculate our battery capacities and available energy we now have on tap. One post here quoted a price on a LiFePO4 battery system at nearly $9,000! It's true. There are a LOT of ready plug and play battery packs out there that cost a small fortune. However we can to better than this if we DIY it. In my case, I was lucky. I found an EV car company that was closing their business in Vista, CA, and paid a little over $100 per battery cell. So I'm in about $3,200 for my batteries. When I am all finished with my battery installation I will be in about $10,500 which includes the motor system, the batteries, a LiFePO4 Battery Management System, battery containment system, 60 volt LiFePO4 battery charger, Victron 700 AH meter, Junsi Cell Logging Monitors, and lastly a pretty funny device I came across; A talking alarm system that tells me in a human voice what event is happening that needs attention. (maybe I'll record my wife's voice! She ALWAYS gets my attention!)

For anyone interested more in LiFePO4 batteries there is a huge thread on here for those using them as a house battery system. It's a great thread and there are some VERY knowledgeable people over there. This will tell you a LOT about LiFePO4 batteries and how to use them. However, there is a difference in the charging methods and management of these batteries when you use them for propulsion. So be aware of that, and much can be learned from the many Electric Vehicle websites out there.

Lastly; I would like to point out that at this present stage of development with electric sailboat propulsion it is not for everybody. The obvious problem for some is the range limitation when compared to diesel inboard power, but, it goes much further than that. If you chose the new LiFePO4 battery installation over the old lead acid (LA) batteries you need to know it is NOT just a matter of hooking up your battery cables and motoring away. LiFePO4 batteries must be thought of as a complete system. While they are an incredible energy source they are also quite demanding on the way you charge them and use them. In my case I have $3,200 invested in the batteries alone. If you don't have a battery monitoring system and you accidentally over charge them, you have just created a very large hole in your wallet from which the batteries and you will not recover. Each individual cell needs to have a cell monitor on it WITH an alarm should the battery get out of the balance zone it likes to be in. Personally, I think at this stage of the game, LiFePO4 might just be a bit beyond the average DIY installation, but if you are serious about learning them, you can save a small fortune by installing and managing them yourself. If you are interested, really take the time to study up on them and go to the thread here >> LiFePO4 Batteries and then search the web for info on them. Also YouTube has some great EV car videos and EV car propulsion and boat propulsion uses many of the same techniques. Good luck!
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Old 21-08-2015, 00:51   #27
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Re: Electric Inboard

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Originally Posted by TacomaSailor View Post
Stefano_Ita said:

"hpev AC motor, lifepo4 wiston battery, 3 kw solar panel on a 46 ft trawler, 3 phase heavy duty generator + 2 14 kwh battery charger each...meaning 28kwh continuos by diesel...it's a long term investment for sure, the pro is always energy available for house load...if you think do a relaxing cruise...6 hours stop on a bay...4 hours motoring...and a new bay to enjoy...and so on"

It still makes no sense!

Please explain to me what is wrong with the following calculations. I may have misunderstood something because I have lived with big 12V solar arrays, Gelcell, and Lead Acid batteries for the last 15-years but no almost nothing about higher voltage LiVFePo4 systems.

Defever 46 foot trawler – assume 40’ LWL and 38,000 pounds with a 15’ beam. It needs 21 HP AT THE PROP to move at 6.6 knots in still water, which is about 15.5 Kw of power.

Let us assume a 48V high efficiency motor in which 100% of battery power gets thru to the prop.

Let us look at a LiFePo4 battery that is currently available for sale. Smart Battery SB200 8D ( 12V Lithium Ion Marine Batteries | Deep Cycle Batteries | Smart Battery® )

It is a 12V battery with a 200-amp hour capacity (8D form factor) with a max 5-hour discharge rate of 180 amps. That means you can withdraw, (until you use up the power stored in the battery), 180 amps per hour without damaging the battery.

At 48 volts and a max discharge rate of 180 amps you can produce 8.6Kw of power.

We would need 4 of those batteries to make 48 volts. Each battery weighs 78 pounds and costs about $2,400. That means the 48V battery bank weighs 312 pounds and costs $9,600.

Cruising at 6.6 knots uses 15.5 Kw and would require two (2) 48 V battery banks or a total of eight (8) 12V 200-amp hour batteries at a cost of $19,200 and 624 pounds of battery.

But, withdrawing 180 amps for one hour from a 200-amp hour battery will discharge it down to a 20% charge. That means you only can cruise for one hour at 6.6 knots before you have to recharge the batteries.

A 48V 50HP high efficiency motor with cables and controller will cost about $3,200.

The 20Kw inverter to power the AC version of that hpev motor would cost about $5,300.

You will have spent $27,700 for a propulsion system that can move the boat at 75% of hull speed for ONE (1 !! ) hour.

And, discharging to 80% of capacity used reduces the life cycle from over 3,500 charge/discharge cycles to fewer than 1,500.

You propose a 28Kw generator, which confuses me because the data sheet shows that a singe 200 amp hour 12V LiFePo4 battery can only absorb 100 amps at 14.6V or a max of 11.6Kw for the entire 800 amp hour 48V system.

The generator will recharge the batteries at about the same rate it is consumed when running at 40% power (14 HP) or about 1.4 GPH. My Yanmar only burns 0.4 GPH while producing 15 HP. You would need at least 1,600 amp hours of battery ($38,400) to accept the generator power at an efficient operating speed for the generator.

The 28Kw generator will cost at least $15,000 so the total cost of your propulsion system exceeds $27,000 and burns twice the fuel as does a direct drive diesel propulsion system.

What then is the advantage of batteries and a generator? In less than one hour (6.6 NM) of cruising on your trawler you will need to be running a 40 HP diesel engine to spin a generator that spins an electric motor that spins a prop, less efficiently that a direct drive diesel.

You plan on A 3 Kw solar array. If you use your 48V electric motor for one hour you will consume 12.5 Kw (15.5 kw to spin prop – 3 Kw produced by the solar panels while underway) of battery power and will require over FOUR (4) hours of PEAK solar power to replace the battery power consumed by one hour underway.

Where do you find five Hours (5) of peak solar panel just when you want to motor in your Trawler?

Sure - battery power backed by a generator works but it very much more expensive and far less efficient than a direct drive diesel. And, there is no reduction in carbon footprint. Those batteries, replaced every couple years under the proposed scenario, have to be made and then recycled, which is very energy consumptive.
Hi TacomaSailor,

Well, let me say this; it's a lot less time consuming and takes a bit less energy to research people that are actually using these batteries for successful propulsion than it is to assume numbers that really don't apply as to how we run our "motors". I've answered Skipmac's post in this thread, and while I am not an expert, I am a very serious DIY'er. I have taken the time to learn quite a bit about the LiFePO4 batteries and I am in the process of installing my system in my Freedom 32 sailboat. Give it a read. I approach the entire thing more from a fun 'make do with less' kind of a deal. Now if I wanted to drive my boat around at hull speed, or needed to do that, I'd stick with diesel, but I don't. It's a sailboat after all, and I am used to having fun taking my time to get where I want to go and that's fine for me. I think you will be surprised at the range we are getting, and it's not a one-hour run time! ;-)
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Old 21-08-2015, 01:05   #28
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Re: Electric Inboard

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Hi Stephanie and welcome to the forum.

- Unless you have .... 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. .
Are you serious? A couple of thousand pounds of batteries? My 32 LiFePO4 battery cells weigh 395 Lbs! You must be thinking ancient lead acid technology. When I removed my old diesel and trans and all the associated diesel related junk I shaved at least 300 Lbs out of the boat.

Now; these LiFePO4 batteries have at least 320 AH capacity. At a 20 amp (3 1/2 to 4 knots boat speed) and 80% discharge rate that gives a cruising distance of about 45 miles. And that is a conservative run time. My batteries actually test at 360 AH even though they are marketed as 320 AH and I try to think of them as such so I have a mental reserve. So really at 360 AH at 90% discharge (still gives 2,000 lifetime discharge cycles) gives me a range of 56.7 to 64.8 miles. How many weekend sailers motor that far on a regular basis? This range makes a LOT of sense for a LOT of people... just saying.
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Old 21-08-2015, 06:35   #29
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Re: Electric Inboard

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Originally Posted by Wireless1 View Post
Are you serious? A couple of thousand pounds of batteries? My 32 LiFePO4 battery cells weigh 395 Lbs! You must be thinking ancient lead acid technology. When I removed my old diesel and trans and all the associated diesel related junk I shaved at least 300 Lbs out of the boat.

Now; these LiFePO4 batteries have at least 320 AH capacity. At a 20 amp (3 1/2 to 4 knots boat speed) and 80% discharge rate that gives a cruising distance of about 45 miles. And that is a conservative run time. My batteries actually test at 360 AH even though they are marketed as 320 AH and I try to think of them as such so I have a mental reserve. So really at 360 AH at 90% discharge (still gives 2,000 lifetime discharge cycles) gives me a range of 56.7 to 64.8 miles. How many weekend sailers motor that far on a regular basis? This range makes a LOT of sense for a LOT of people... just saying.
Hi Wireless,

First, thanks for the very detailed posts on your electric installation. Not only detailed but I think accurate and balanced as well.

When I tossed out the 2000 lbs comment I was thinking FLA batteries, not LiFePO. As you mention, LiFePO are not exactly plug and play and could be beyond the abilities of many cruisers. Even with my background in EE I see the switch to LiFePO as quite demanding, very time consuming and the possibility of a small slipup trashing thousands of dollars worth of batteries a huge concern.

I think we both agree that the bottom line is electric has some great benefits but also some significant shortcomings.

As I see it:

Benefits
- quiet
- lower maintenance
- ease and flexibility of the installation
- instant power
- possibly weight savings depending on the type and number of batteries installed.

Negatives
- limited range and/or limited speed
- cost You said you got a great deal on the batteries but your cost still approached that of a new diesel engine installation. Add the cost of a generator to get range and the cost will be double or triple the cost of a straight diesel installation.
- could be left with no power in a critical situation. What do you do if you have run to max range, batteries flat and you have to move the boat for some emergency?

At this stage what is stopping me from going electric is range and cost.
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Old 21-08-2015, 06:55   #30
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Re: Electric Inboard

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Originally Posted by Wireless1 View Post
Are you serious? A couple of thousand pounds of batteries? My 32 LiFePO4 battery cells weigh 395 Lbs! You must be thinking ancient lead acid technology. When I removed my old diesel and trans and all the associated diesel related junk I shaved at least 300 Lbs out of the boat.

Now; these LiFePO4 batteries have at least 320 AH capacity. At a 20 amp (3 1/2 to 4 knots boat speed) and 80% discharge rate that gives a cruising distance of about 45 miles. And that is a conservative run time. My batteries actually test at 360 AH even though they are marketed as 320 AH and I try to think of them as such so I have a mental reserve. So really at 360 AH at 90% discharge (still gives 2,000 lifetime discharge cycles) gives me a range of 56.7 to 64.8 miles. How many weekend sailers motor that far on a regular basis? This range makes a LOT of sense for a LOT of people... just saying.
If you are willing to accept 3.5kt crusing speed, you need to drop the diesel down to maybe 3-5hp and take into account the improved efficency to do a comparison. Now you might be talking about 45miles on a couple gallons fuel. A fairly typical 100 gal tank would provide ocean crossing capability.

Of course, if you get into a storm and your sails blow out, your system will be SOL trying to hold you in place. Or if you take it up to a half way reasonable cruising speed and your range drops back the 5-10miles we've been talking about.

For a die hard doing it just to prove they can use electric, 3.5kt cruising speed is fine. For a cruiser looking for the best all around propulsion system it's not viable and that's why retail systems haven't taken off.
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