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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Electric/Hybrid
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  #21  
Old 02-07-2014
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Re: Repowering with an electric engine?

here are stats i got from Electric Yacht, 5kw motor on C&C 27. if keep speed to 3 kts, these have great range

Flooded AGM LiFePo4
200 ah 200 ah 200 ah
Kts Hrs Nm Hrs Nm Hrs Nm
3.0 16.6 50 16.5 49 16.5 49
3.8 7.0 26 7.6 29 8.0 30
4.8 3.0 14 3.5 17 3.8 18
5.4 1.8 10 2.2 12 2.5 14
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  #22  
Old 02-07-2014
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Re: Repowering with an electric engine?

50nm is great range? You can easily sail farther than that in a day.

I think that the practicality of an electric motor for a sailboat depends on how you use the boat. I do a lot of cruising on vacation time, so I do need to get home on schedule. I can easily sail 70nm in a 12 hour day and do 1-2 week cruising vacations. I need to know that if I leave in a period of strong wind that I can motor back if necessary. That doesn't mean motoring at 3 knots (half of my normal cruising speed) or on short days.

If I were not going back to work and sailing around the world without a schedule it would be easy to operate motorless or with a short capacity electric motor. As someone with regular employment and fixed vacation schedules I don't see any option other than diesel or gasoline that is practical.

If I sailed on a lake or only used the boat for short day sails then electric would be a great option.
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  #23  
Old 02-07-2014
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Re: Repowering with an electric engine?

Quote:
Originally Posted by whippet99 View Post
here are stats i got from Electric Yacht, 5kw motor on C&C 27. if keep speed to 3 kts, these have great range

Flooded AGM LiFePo4
200 ah 200 ah 200 ah
Kts Hrs Nm Hrs Nm Hrs Nm
3.0 16.6 50 16.5 49 16.5 49
3.8 7.0 26 7.6 29 8.0 30
4.8 3.0 14 3.5 17 3.8 18
5.4 1.8 10 2.2 12 2.5 14
Is that running your batteries down to there full capacity (often how numbers like this are stated when trying to sell a system), if so then you will be replacing the batteries a couple times a year. You don't want to take them down past 50% capacity. And at 3 knots you will have to have some pretty good patience, and no head winds, or wave action to go through. I think that is what will kill the range really fast.
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  #24  
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Re: Repowering with an electric engine?

Stats at 80% Depth of Discharge

I have been discussing with those that have done this, and they are happy. Battery life is multiple years, not months. Maintenance considerably less.

Of course, it depends on your application. I need to get out of marina, motor in the calm, otherwise i'm sailing. I have shore power for recharge. That's why when the Atomic 4 finally gives in, I'm switching
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Old 02-07-2014
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Re: Repowering with an electric engine?

Quote:
Originally Posted by whippet99 View Post
Stats at 80% Depth of Discharge

I have been discussing with those that have done this, and they are happy. Battery life is multiple years, not months. Maintenance considerably less.

Of course, it depends on your application. I need to get out of marina, motor in the calm, otherwise i'm sailing. I have shore power for recharge. That's why when the Atomic 4 finally gives in, I'm switching
I for one would love to see how they got to those numbers and at what voltage this bank is... It seems like someone forgot about our buddy Peukert in those equations......

You might get multiple year out of LifePO4 at 80% DOD but not a heck of a lot out of FLA or AGM... Even the best AGM's can only claim 400 cycles to 80% DOD but that IS IN A LABORATORY.. Real world, not lab derived under carefully controlled conditions, 80% DOD numbers barely break 200 cycles for lead acid...


To go 50nm takes 16.6 hours at 3 knots

A 5kW motor is pulling 104A at 5000W at 48V

If we figure you are using only 70% of that 5kW to do 3 knots that is a 73A load to the battery bank...

A 73A load on a 200Ah 48V bank with a 1.11 Peukert (AGM) gets you a 159Ah bank not 200Ah.. This must always be accounted for in good system design.

If you want to use 80% of the bank capacity at 73A you need to start at a Peukert corrected capacity of 159Ah's NOT at 200Ah's or you will be drawing the bank WAY below 80% DOD due to the high loads applied to it, which are well beyond the 20 hour rate for lead acid of 10A, which the bank was rated at.

So you have 127 (actual) Peukert corrected Ah's to use before you hit 80% DOD with a 73A load with an AGM bank (Lifeline).

If each hour of run time at a 70% load burns 73Ah you can't even go 5 miles at 3 knots before hitting 80% DOD....


Even if we figure the motor at just 50% load/52A/48V you have a 165Ah bank and 132 usable Ah's before hitting 80% DOD with a Peukert of 1.11...

Even a 50% load still barely gets to 7nm....

At 1000 watts or just 20% motor load you are still burning 21A at 48V.

21A X 16.6 hours/50nm = -348.6 Ah's consummed...

I see no way you can get 16.6 hours out of a 200Ah bank even at just a 20% load....????


It is late in the day and I am assuming a 48V pack but can someone please double check my math....
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Re: Repowering with an electric engine?

Quote:
Originally Posted by mitiempo View Post
Sails are alternative energy.
That's why I sail instead of using a motor.
The Zen 24 from japan is kind of an interesting boat. I have only seen one review and some magazine advertisement. I am not sure a (Zen 34 or 44 would work, Hybrid cars and pure electric are on the horizon. Sailors are innovative despite clinging on to the old ways of moving with just the wind. Japan does not have a lot of resources compared with the other places in the world and this may drive the innovation of alternatives.
Who will be the, and what will be the innovation of the future? Who will be left behind ? It is ok if it is a choice to enjoy an old boat, or a classic corvette, A choice to be left behind in the (race to space) because we are complacent and just continue using an internal combustion engine with out a thought to an alternative would be sad.
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Re: Repowering with an electric engine?

The Zen 24 looks like a nice daysailer/weekender and seems very well built and equipped. But the electric propulsion is an $10,680 option without batteries. You would still need to plug in to charge any appreciable amount. The Yanmar diesel at $11,100 is a much better value and will give a much longer range under power at lower cost.

Nice boat but nothing new really.
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  #28  
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Re: Repowering with an electric engine?

Thanks Maine Sail

Good research and questions. I will try to get more info from vendors and those that have gone electric.

BTW, yes you are correct about 48V assumption.

Are you the famous Main Sail that did the great job on Stuffing Box maintenance photos? A cult hero in various forums
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Re: Repowering with an electric engine?

Quote:
Originally Posted by whippet99 View Post
Thanks Maine Sail

Good research and questions. I will try to get more info from vendors and those that have gone electric.

BTW, yes you are correct about 48V assumption.

Are you the famous Main Sail that did the great job on Stuffing Box maintenance photos? A cult hero in various forums
I don't know about the "famous" or "cult hero" but yes, same guy...

The only thing I can say to help you keep everyone around you honest in this endevour is to:

Trust Ohm's Law - Many here and elsewhere try to re-wire it, but as of yet no one has been successful.. For your use a useful calculation is below...

Convert Watts to Amps at fixed voltage:

Watts ÷ Volts = Amps

eg:
5000W ÷ 12V = 417A
5000W ÷ 48V = 104A


Never Forget Peukert - When dealing with high load applications such as e-boats one simply can not ignore Peukerts Law when dealing with lead acid batteries..

A 100Ah lead acid battery is only a 100Ah battery when used at and loaded at 5A at 80F, when new or just broken in.... Every other load & temp range either above or below the 20 hour rate at 80F results in CHANGES the batteries 20 hour rated Ah capacity! Cycle life and DOD also impact Ah capacity.. Anyone telling you otherwise is really not qualified to be doing so.

LiFePO4 cells have minimal Peukert's corrections but they are still not a Peukert of 1.0..... A 100Ah battery with a 1.0 Peukert would provide 100Ah at a 300A load and conversely 100Ah at a 0.5A load. This simply does not exist in the real world... The reality is that it might provide about 80Ah at 300A and 115Ah at 0.5A..

Do that with a flooded lead acid 100Ah battery:

100Ah Battery 300A Load = 33Ah
100Ah Battery 0.5A Load = 186Ah
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  #30  
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Re: Repowering with an electric engine?

Quote:
Originally Posted by whippet99 View Post
here are stats i got from Electric Yacht, 5kw motor on C&C 27. if keep speed to 3 kts, these have great range

Flooded AGM LiFePo4
200 ah 200 ah 200 ah
Kts Hrs Nm Hrs Nm Hrs Nm
3.0 16.6 50 16.5 49 16.5 49
3.8 7.0 26 7.6 29 8.0 30
4.8 3.0 14 3.5 17 3.8 18
5.4 1.8 10 2.2 12 2.5 14

What would be an estimated recharge time with 1000watts of solar? Days, weeks, months?
Thanks
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